Dive deep into how HeatPumPro works with this training session on HeatPumPro setup and troubleshooting. Learn how to set all of the parameters in the setup wizard, and how to troubleshoot common issues with the system. You'll learn how to tell if the problem is with the Arzel system or another component. We'll briefly examine setup and troubleshooting for AirBoss and MPS zone control panels too. (To skip to the section you need, click "View on YouTube.")
The HeatPumPro is a universal panel. It’s not just for heat pumps. It’s for anything from single-stage conventional all the way up through multi-stage dual fuel. As long as your system is compatible with a non-communicating thermostat and can use traditional 24-volt inputs: R, W1, Y1, Y2, W2, G, O, common. As long as your system is compatible with that, the Arzel HeatPumPro is going to be your go-to panel for anything four zones and less.
It offers a lot of customization for the contractors. As far as the staging parameters go, if you have a heat pump system, that can be staged based on your leaving air temperature. And when it comes to your W2 Y2 outputs, the HeatPumPro allows you to disable that W2 Y2 based on the size of your zones. So if you have a smaller zone, you don’t want to run 100% capacity through that equipment, the Arzel HeatPumPro with its zone weighting capabilities, will allow you to set custom percentages for each of your zones to enable or disable W2 Y2 based on the number of calling zones. And it can mix and match, so it might be that one zone’s large enough, another zone requires a little extra capacity, and then two zones are small enough that you wouldn’t want them, even calling together, to be able to use second stage capacity. So all that can be set up from the same panel, and it provides you with a true customization using the Arzel zone weighting capabilities.
It works with all equipment types. So if you need just a single stage gas furnace with a condensing unit, the HeatPumPro is compatible. If you have a two-stage, or even a non-communicating modulating furnace with a heat pump, the Arzel HeatPumPro is compatible. And with that, you can use basic thermostats.
The operating parameters are field adjustable. They’re stored in nonvolatile memory, so if the power goes out, somebody resets the panel, turns the power off, the settings will not change unless somebody physically changes the settings in the wizard. So they are nonvolatile memory and they will not change unless somebody specifically changes the settings. The vast majority of the parameters are field adjustable so you can really tailor that comfort to your customer’s expectations.
We have high and low temperature protections, so if the coil is going to start to freeze up, we can stage the compressor back. If the furnace is getting too hot, we can stage it back. And if it stays in those conditions, we can turn off the compressor, we can turn off the W outputs, and we still continue to run the fan so that we can cool off that heat exchanger, or that we can keep heat moving through that evaporator coil from the house air, so that it doesn’t turn into a block of ice. So we do have temperature protections built in into it.
Those are also used for staging so if we can’t maintain a certain temperature in our leaving air duct the heat pump will stage up. If we can’t maintain a certain temperature in our leaving air duct the air conditioner will stage up. And if we have electric backup, we can bring that in based on the leaving air temperature. If we have a gas furnace back up, there is a 9-minute delay between first and second stage heat, but W2 has a hard lockout based on the zone weight. So if that zone cannot handle W2 output, the HeatPumPro will keep it disabled indefinitely until the zone weight percentage adds up to being allowed, or there’s enough duct work available to handle that high stage capacity.
We also have the balance point changeover built into the HeatPumPro, so you don’t have to use heat pump thermostats. It’s all controlled through the HeatPumPro itself. You can use a basic, one heat, one cool, R, W, G, Y, common if you need it, thermostat, and the HeatPumPro will give you up to four heat, two cool on your outputs for an all electric application with a two-stage heat pump and two-stage electric backup heat. Or if you have a gas furnace with a heat pump, it will provide you that dual fuel changeover as well as the staging control for that furnace and the outdoor unit.
So the zone weighting controls the W2 Y2 output to the furnace air handler independently of the Y1 Y2 to your condensing unit. That allows us to match the airflow more closely to the size of duct work that’s available. So by using the zone weighting there’s two sets of Y contacts in the HeatPumPro: air handler Y1 Y2, so that would be our furnace, or that would be our air handling unit; then condenser Y1 Y2. The air handler contacts are zone weight based, so available duct work to match the blower speed to the available duct work as much as possible, and then the condenser contacts are temperature-based. So if our leaving air temperature, heat stage, cool stage threshold cannot be maintained, then the condenser can stage up.
One of the things this does for us, is when the weather gets cold outside, we know that heat pumps have a curve: the colder it gets, the less heat they can produce. But if we have a smaller zone calling we might want to keep low stage blower running to it. But it’s colder outside, so we might want to run that compressor at a higher capacity to pull more heat from the air outside. We can do that, and that’s going to help save electricity because we’re going to spend less time running our electric strip heat and more time using our condenser to pull that heat from the air outside.
LCD screen and programming: the LCD screen gives you a high-level overview of everything that the HeatPumPro is doing. The very main screen, the home screen essentially, it has a line that says OUT. That tells you exactly what terminals are energized going to your equipment. If it is listed there it should be closed on your HVAC outputs. We can look directly underneath that at the OAT and the LAT, outside air temperature, leaving air temperature. We can take a look and see if those are within range. We can see exactly what zones are actually calling. So if I look at those zones and, let’s say I’ve got two zones calling, but I only see one of them being registered in that zones box. Then I’ll know that there’s a problem with that other thermostat that’s calling. And now I can go through my individual zone screens.
When I’m troubleshooting with the HeatPumPro, the first thing I’m going to do is, I’m going to look at my home screen. If I know my thermostats are calling, I’m going to take a look at that output line and I’m going to see. Is the HeatPumPro panel telling me it’s outputting for what I wanted it to do? So if I know my zones are calling, I’m going to look at that zones box, and I’m going to going to see if the number displayed there reflects the zone thermostats I turned on. And then I’m going to look at my output line to see if that reflects what I told my thermostats I wanted to happen. And if those don’t match up, then I’m going to go through my individual zone screens.
I’m going to use that blue enter button and I’m going to cycle through the zones one at a time. The first screen I’ll see is zone one, and each press of the button will take me to a different zone thermostat. Zone one, zone two, zone three, and zone four.
Occasionally we’ll see a “-ILL.” that’s an illegal call that the panel will ignore. In that case zone four says “WY-ILL.” That tells me that I either have a short in my thermostat wire, so W and Y are pinched together, or I have my thermostat programmed incorrectly and it’s calling for Y at the same time it’s calling for W. Maybe I set my zone 4 thermostat up as a heat pump thermostat, but the zone four connections will not accept a heat pump thermostat. It has to be conventional, one heat, one cool for zones 2, 3, and 4. Now the zone one thermostat connection will allow for a heat pump thermostat, but it’s completely unnecessary. We can set the panel to use conventional inputs at zone one, so all we need is R, W1, Y1, G, and common if it’s necessary. Maybe we have a Wi-Fi thermostat. We prefer you to have the five wires available so you can have a dedicated common wire for the Wi-Fi thermostats.
So based on how I set it up looking at these individual zone screens I can see exactly what inputs I’m receiving from my thermostat. So if I know I have zone 4 calling, and I go to my zone 4 screen and I see a “-ILL,” that tells me I have a problem with the input coming from that thermostat. That’s either an issue with the thermostat: might be programming, might be a bad thermostat; or it’s an issue with a short in my low-voltage wiring, and now I can focus my attention at zone four to see what’s going on. When we’re diagnosing the HeatPumPro, or any Arzel panel for that matter, when we look at that, our thermostat inputs, so zone one, zone two, zone three, zone four connections; we can treat that like it’s four individual pieces of equipment. So our thermostat’s our thermostat, and that zone connection is essentially our equipment in relationship to our thermostat. And then we can treat our HVAC outputs as though it’s a thermostat. So the HVAC outputs in relationship to our furnace and air conditioner is a thermostat, and we can split that up and diagnose each each side of the system independently, looking at it as though we had four or five pieces of equipment instead of four or five zones, and now we can we can focus our attention on the actual trouble spot instead of becoming confused jumping back and forth between all these different areas.
So the HeatPumPro will show us what zone we’re having a problem with. It’ll show us exactly what the panel is supposed to be doing, and then we can focus our attention on diagnosing that certain area that needs to be addressed.
Then the last screen we see is HPP status messages. If you have a fossil fuel furnace, it’s always gonna say below balance point, because if you don’t have a heat pump outside, it’s going to be locked in back up, and anytime a call for heat comes in, it will always say below balance point. So a common question I get for somebody that’s not as familiar with these panels as those who have been installing them for a long time is, “The MSG is flashing in the bottom of the main screen.” That’s not a problem with the equipment. It’s always gonna say below balance point if the gas furnace is running. Always going to say below balance point if the gas furnace is running. And then capacity stage up would just mean that we didn’t reach our heat stage threshold, we didn’t reach our cool stage threshold, so we’re stepping the equipment up a stage. So it’s not an actual fault with the equipment operation. It just tells you what the panel has done most recently, whether it’s allowed for W2 Y2, or whether it’s caused it to stage back because you hit a limit condition, or if you have a gas furnace without a heat pump that “below balance point” is always gonna display. So it’s it’s not a problem of an error, it’s just what the panel’s done recently for operation.
So when you first power the panel up, you see that screen, it’s going to say HeatPumPro by Arzel, press blue to enter setup. So you’re going to press the blue enter button and if for some reason your panel has the blue button and the yellow button reversed just look for enter. It’s always there on the right side of the two white buttons. So just press the enter button.
The first parameter we’re going to see is “show temperature in” and then we select Fahrenheit or Celsius. So for America, we’re primarily Fahrenheit; Canadian markets, primarily Celsius, and you can select that operation here.
You can select your zone priority. Automatic as factory default and that’s going to take care of the vast majority of people out there. But there are some who need to set a priority to heating/cooling, because maybe they’ve got someone in the house on oxygen in that zone, needs to take priority over the other zones as far as comfort goes. So if that person needs more heat they would set the priority to heating, and then if that zone calls for heat, it would be served first. It would take priority. Or maybe they need more cooling in that area. Someone with COPD. My buddy’s moms got that and she can’t handle it if it gets too hot. So, for her, we would set it to a cooling priority. That way she can be comfortable and the rest of us that are healthy are able to be uncomfortable for a slight period of time to manage her requirements for her health.
Zone weight priority allows you to set a hard lockout on the changeover, so the panel, whether you’re set to automatic heating or cooling, after 20 minutes of serving that priority zone will switch to the opposing call. However, if you’re set to zone weight priority, it’s a majority rule system, and if the majority of calls coming in are calling for heating and that zone weight percentage says that, then the heating call is going to be served indefinitely before that cooling call can be served, if a small percentage is calling for cooling.
Then we have our Zone 1 stat type. So this is where we determine, did we use a heat pump thermostat at zone one, or did we use a heat/cool? Factory default is heating/cooling. If we use a heating/cooling thermostat, a call for heat is W. If we use a heat pump thermostat the call for heat might be W, but a call for heat also could potentially be Y, Y1, and G. So if it is set to heat pump, the call for heat could be Y1 and G, a call for heat could be W1, both will be served the same. However, we cannot energize O and W one at the same time. If we do that, the panel will have an illegal call. So “-ILL” and it will ignore zone one. This is a common cause for tech calls when it comes to somebody installing a piece of equipment that energizes the reversing valve in heating. They don’t read the installation manual, and when they forget to do that, they set their thermostat up to energize the reversing valve on a call for heating, and then that that zone 1 thermostat is not being served. And it’s not being served because they energized O and it’s too cold outside to run the air conditioner. It’s got its low ambient lockout. Or they energized O and they back up heat at the same time because they turned the thermostat way up and it’s calling for back up heat. And then the panel views that as an illegal call because O is only ever energized from the thermostat on a call for cooling.
And here we get to our individual zone weights. And when I look at the zone weights, I don’t really need you to set that up as this zone is exactly this percentage of duct work available to equipment capacity. I like to use whole numbers: 50, 40, 20. If I’m set to 50%, the setting that I go to next is air handler stage threshold, factory default 50. So if my zone weights are set to 50%: 50 is equal to 50, W2 Y2 is allowed. If I set it to 40%: 40 is less than 50, W2 Y2 are disabled. I require at least two zones to call before I can use second stage capacity. And then if I set it to 20%: 20 is less than 50. But if I have two zones set to 20%, 20 and 20 is 40, 40 is less than 50, W2 Y2 outputs would be disabled until at least three zones were to call.
So we can set all that up. Each zone can be customized for its individual weight to determine, do I need 1 zone to call? Do I need 2 zones to call? Or do I need 3 zones to call? All of that can happen from the exact same panel.
So if I have a four zone system, zone one’s a large zone, I leave it at 50%. Zone 2 is a medium sized zone. It can’t quite handle second stage capacity, but it could if it had just a little bit more. I would set it to 40%. And then zones three and four are small. I don’t want them to run second stage capacity even if they call together. I would set them for 20%. With Zone 2 calling, needs a little extra capacity, 40 and 20, so zone 2 and zone 3, or zone 2 and zone 4. 40 and 20 is 60, 60 is greater than 50, W2 Y2 is allowed. However, zones 3 and 4, 20 and 20 is 40, 40 is less than 50 W2 Y2 is disabled.
So I just use whole numbers: 20, 40, 50. Fifty is factory default, I leave it alone. If I want 2 zones to call, I set it at, or if I want a medium sized zone and a small zone, I set it at 40%. But if I have two small zones I set them for 20% and then that allows me to have a more customized operation as far as my W2 Y2 output goes for that piece of equipment.
Air handler stage threshold works very closely with the with the zone weighting because that’s the threshold where I have to add up this number of zones to be equal to or greater than, and once I reach that threshold, W2 Y2 outputs to the furnace air handler are allowed.
Y2 air handler outputs will happen right away. The reason is because it says, “I have all this duct work, I need to give it as much air as I can.” Y2 output happens right away. So we instantly get Y1 Y2 going to the furnace air handler. However, the condenser contacts are temperature based and we set those next.
The gas furnace, once my zone weight threshold is met, there is a 9-minute delay before W2 is allowed to energize. So there has to have been a heating call for 9 minutes and then I get a W2 output if my zone weight threshold is met, or my air handler stage threshold is met.
Heat stage threshold: factory default’s 88°. This is my stage up threshold for a heat pump. If I cannot maintain my leaving air temperature at 88°, I get a Y2 output after three minutes of operation. If I still cannot maintain my heat stage threshold after an additional 3 minutes, I’ll get a W1 output if I have an all-electric system. If I don’t have an all-electric system, I’ll switch over to the gas furnace.
Cool stage threshold: 55. So if my air conditioner cannot maintain 55° with the Y1 input then I will stage it up to Y2, and I’ll run a second stage compressor. And that works independently of the blower operation. So I might run a low stage blower. But if my outdoor temperatures are extreme enough, I can run my compressor in that higher stage to either remove more heat from the house or to pull more heat from the air outside and move it into the house, if I have a heat pump or condensing unit.
Balance point OAT: this is our changeover from heat pump to fossil fuel back up. If we don’t have a heat pump, it needs to be set to lock in back up, and that is the factory default. If we do have a heat pump, this is our changeover from heat pump to fossil fuel back up, and once we reach that temperature, the heat pump’s disabled. We only run the fossil fuel backup.
Resistance lock OAT: efficiency setting for the all-electric applications. With heat pumps becoming more and more efficient, we don’t need to run the strip heat until we get colder and colder temperatures. We can save our customers a lot of electricity by disabling that electric backup heat until we reach a specific temperature outside. So while the HeatPumPro does control that pretty effective based on leaving air temperature, there might be a reason to disable the electric backup heat completely until we reach a specific outdoor air temperature, and that can be done.
And we have our heat pump high limit. If our compressor running gets too hot, we’ll stage it back. If our compressor running stays too hot, we’ll stage it off, continuing to run a Y1 output to the furnace, with a G output as well. And then our gas furnace or electric strip heat. If those get too hot, we can stage them back. If they stay too hot, we can stage them off. Between all of our staging, there is a 3-minute delay, so the panel will wait 3 minutes between staging it back, before it stages it off, and it gives it that 3 minutes to drop below the threshold.
And then our cooling LAT low limit: freeze protection for our coil. If our plenum temperature dips below this we’ll stage the compressor back. If it stays below there we’ll stage the compressor off.
Type of back up heat: Are we using fossil fuel backup or are we using electric? If we’re using fossil fuel backup, we cannot run Y output to the condenser at the same time as a W output. If we have it set to electric, then W becomes a stage of Y. So first stage heat would be Y1, second stage Y2, third stage W1, fourth stage W2. However, if we are set to fossil fuel, we cannot run W and Y at the same time. It will either be Y1 Y2 compressor, or it will be W1 W2 furnace.
Backup controls fan: true or false? If it is set to true, the backup controls fan. If it is set to false, the Arzel panel will output for G, so fan call. It will output for G on a call for heat.
Dehum caller voltage: leave it set to 24VAC. I like to call this poor man dehumidification because what it does is, if you engage dehumidification through the Arzel panel. So there’s a D terminal, D for dehumidification, at your zone 1 connections. If you engage that, then the panel will run a Y1 compressor output. It’ll run a G output to the furnace air handler, so you get low speed fan, really cold coil, and that runs the that that runs the air through the coil, collecting as much humidity as possible, because that coil is really cold, and that allows it to dehumidify the air. If you leave this to 24 volts, you would use a dehumidistat to engage R and D. So your hot, and your D for dehumidification at your zone terminals. If you set that to 0VAC, you can use a humidistat and it essentially reverses the operation of that humidistat. However, if you don’t have anything connected, can you set that to 0VAC, the panel will indefinitely have a dehumidification call and your compressor will run all the time when there is no active call from the thermostats for heating or cooling. So basically leave that set to 24 volts. Don’t touch it unless you plan to use it. And if you plan to use it, use a dehumidistat.
Secondary purge time: the panel has two purge cycles. The first purge cycle, primary purge cycle, is a 2-minute cycle at the end of a call for conditioning. It maintains the dampers to the last calling zone open for two minutes, and then after that 2 minutes it goes into a secondary purge cycle. And that secondary purge cycle now de-energizes every zone solenoid, continues to run the pump for this period of time. So 60, as in 60 seconds. Runs the pump for that period of time to drive the dampers open on the entire system. And then the pump will shut off and the dampers will rest in that position.
Dehum cycle time: how long does our compressor Y1 output run on a call for dehumidification? We can set that for 5,10, or 15 minutes. The longer we set it, the more humidity we’ll remove, but the greater the potential is for over cooling. The lower we set it, the less humidity is removed, but the potential for over conditioning is limited to some extent.
Cooling low ambient lockout: it’s too cold to run the compressor. Let’s disable it for cooling calls. So if we’re below that temperature and we get a call for cooling, we’ll run Y1 output to the furnace air handler, but we will disable condenser Y1 output on a call for cooling. That does not apply to heat pumps calling for heat; only to the desire for cooling.
Here is where we select our reversing valve. I mentioned earlier our thermostats are always, always, always, always energized on a call for cooling. Doesn’t matter what brand of equipment you have. Any Arzel panel, the thermostat always has to energize on a call for cooling. However, the HeatPumPro allows you to select the O/B terminals operation. So you can select your need here by setting it to heating or cooling. If you have the AirBoss or the MPS panel, the O Terminal and the B terminal are separated out. And you would connect your reversing valve to its respective terminal. So if you’re energized in heating with the AirBoss or the the MPS panel, you’re going to hook up your reversing valve from the heat pump at the B terminal, B as in boy. If you’re energized in cooling with the AirBoss or the MPS, you would hook it up to the O terminal. But with the HeatPumPro, the O and B terminal are combined, and in the setup wizard you select its operation here.
Use balance point for electric. You can leave it set to false. If you had an all-electric system and you wanted to provide a hard lockout for your heat pump system, you could do that. Your balance point OAT you would set for that temperature. You would set the use balance point for electric to true, and then once you reach that temperature for your balance point OAT, it would disable the heat pump and only allow for the backup source of heat to operate.
And then we have demo mode. The demo mode speeds up all the timers in the board by a factor of 12, so leave it set to false or you will short cycle your equipment, potentially damaging it.
The setup worksheet: Because the settings are stored in non-volatile memory, write them down. That way you have a record of where they were at, and if somebody were to go in there and start changing settings, you’ll know we set them here. Somebody’s been in there adjusting them and they’re different than what we originally set. So record where your settings are at. If something’s different, you can start to look at why. Maybe somebody adjusted the settings. Maybe it was to tailor the comfort for a different expectation. That’s possible, but record all your settings here. It’s on the backside of all the manuals and that’ll provide you with a helpful diagnostic tool in the future. But also if you were to have to replace a control board, maybe the unexpected happens and we send you a control board under warranty and you want to make sure that the settings are what the old one was. It really helps to have them written down. That way you’re not guessing at where it was set at and you’re not having to interview your customer to reset everything out the way that they expected it to operate. So records, records are very important.
Then the illegal calls. Common illegal call, especially at the start of spring when the air conditioning season comes in, is “Y-ILL.” The question comes to be why is Y illegal? Well, it’s illegal because you’re missing G. So if you want to call for cooling you have to energize Y and G at the same time.
Now some of the things that people do: they have a Wi-Fi thermostat and they rob the G terminal for their common. That can happen. If you do that, make sure you install a jumper at the thermostat connections inside the panel between Y and G, because if that G terminal is not energized, the panel will ignore it as an illegal call.
The other common illegal call is “WY-ILL.” that’s usually a pinched thermostat line, or somebody has a thermostat at zone 2, 3, or 4 that’s trying to operate like it’s a heat pump thermostat, and the panel will not respond to that. Zones 2, 3, and 4 are conventional one heat, one cool thermostats only. You can use Wi-Fi if you want to. So if your customer wants that Nest thermostat, they want that ecobee thermostat, or the the RedLINK thermostats that Honeywell offers, those are all compatible, but you’re going to set them up as a one heat, one cool, conventional R,W,Y,G, common if you need it. And if it’s a Wi-Fi thermostat, we strongly recommend having a dedicated common wire.
Now zone one connections do allow for heat pump thermostat; completely unnecessary, as we saw in the setup wizard, you can select that operation. If you have it selected for heat, cool within the setup wizard, the call for heat is W. If you have it set to heat, cool the call for cooling is Y and G. If you have it set to heat pump, the O terminal gets energized on a call for cooling, but a call for heat could be Y and G, a call for heat could be W1. A call for cooling is always going to be Y1,G, and O if it’s set to heat pump.
So for the sake of confusion, cause myself personally, I’ve run into a lot of technicians that that seem to have a hard time grasping reversing valve wire for some reason. I was a field tech for 13 years before I came to Arzel and in my time as a field technician, it always amazed me how many technicians were confused by adding that extra O wire to the thermostat configuration. So for the sake of confusion, just leave everything set up as a heat, cool, R, W1, Y1, G, common, and the panel itself will control everything from the outputs.
And then we have a recommended settings worksheet. This is available to you through our contractor portal. This is also included in our installation manuals now, so if you get the new installation manuals, the settings worksheet is included in there. It gives you your equipment configuration across the top. So single stage, fossil fuel, air conditioner, all the way up through the inverters with all-electric or the inverters in a dual fuel heat pump application. And then it gives you the settings going down the left side of the spreadsheet there. That settings worksheet is our recommendation based on most common practice, and you can set your settings accordingly.
Arzel diagnostic: our HeatPumPro. Our panels all look different, but the basics for diagnostic are all the exact same. You have your zone inputs, you have your HVAC outputs, and when we start looking at it, our zone inputs are the equipment connections in relationship to our individual thermostats. And then our HVAC outputs are thermostat connections in relationship to our equipment.
The panel configurations differ slightly, but we have all our thermostat inputs. We have our HVAC outputs. Our AirBoss and our MPS are a slightly different configuration. We have our thermostat inputs, our zone inputs, and then we have our MPS, we have our zone inputs as well, 1, 2, and 3. And then we have our HVAC outputs. And while the configuration between the different panels varies somewhat, they all operate exactly the same. Your thermostat calls, the panel applies a set of rules, and then your equipment provides you with the output.
So, zoning applied. Thermostats call, your equipment, in relationship to your thermostats are your zone connections. The zoning panel applies a set of rules to it, so we’re not sending conflicting calls to our equipment and potentially damaging it. So that set of rules then determines what our equipment’s going to do and then our HVAC outputs are energized accordingly so that we’re not sending a conflicting call to our equipment. So the thermostat calls, the zoning panel applies the rules, and then the zoning panel acts as the thermostat in relationship to our equipment, as the mediator applying some logic to multiple thermostats.
But before we can really get into how those rules apply, we have to have the basics of electrical diagnostic worked out. And this is probably one of the common things that we do here in tech support. We go through basic low voltage diagnostic almost every single day. Technicians get in a hurry, and I’m guilty of it myself, we get in a hurry and we stop looking at some of the basic rules of diagnostic, and then we misdiagnose things. So to try and help technicians not be parts replacers, we put together this training session for them to help them grasp the basics of low voltage diagnostic. From there, they can build out to become really effective technicians.
When I really started to understand how the low voltage circuit works and how to properly test it, I was able to take that and apply it to just about everything I worked on. And it became so much easier for me to understand complex circuits, and even build out from there to potentially even bypass the control temporarily so I can get somebody’s heat working in the middle of winter, while I ordered the part that I needed to get it fixed. So there are very few instances where I would have to leave a customer without heat because I understood how how relays work. I understood the basics of the low voltage side of it, so I was able to build out past that to maintain all the safety circuits within that furnace, but cause it to still operate that they could have heat for an emergency situation while I ordered a part for them.
Relays take many shapes and forms, and some of the ones that we’re popular with we can see here. In that bottom right hand corner, that’s a common relay that we run into. Probably have three or four of those on most service trucks, and they’re a lifesaver, they really are. Some of the other common relays: the brown one there, an old fan center relay. We still run into those on occasion, but not too often. More commonly with a fan center when it comes to a boiler, but even boiler controls are being updated to the point where those relays are really becoming obsolete.
Relays take many shapes and forms, and a relay is really just an electrical device that incorporates an electromagnet to activate a circuit; close a switch. So it’s a light switch, but it’s an automatic light switch. You apply power to one side of it, the light switch closes. Or opens depending upon what we’re looking at: normally open or normally closed. You apply power to it, and then the normally open / normally closed reverse function and they either open or close.
The difference between a relay and a contactor is the amount of current flowing through it. Contactors are typically designed for loads of greater than 10 amps. Relays are typically designed for loads of less than 10 amps. Aside from that, they both operate almost exactly the same. It’s just the size of the contacts to allow for greater electrical current.
The most common relays that we work with in the residential and light commercials: the SPST: single purpose single throw, or the SPDT: single purpose dual throw. More commonly, the ones on the back of our truck are going to be an SPDT because there’s a normally open set of contacts and there’s a normally closed set of contacts. Nine times out of ten, that’s the relay on the back of a service technician’s truck, and that’s the one we rely on the most in our industry, because it has both sets of contacts that we can use to meet just about any application. Normally open normally closed is a lifesaver to the technician.
But a relay? You got an electromagnetic coil. You got points of contacts. And then when that coil is energized, it pulls the magnet down to make the contacts or to break the contacts. So, in its normal condition the relay might be open. In its power condition, the relay would then close, depending upon what we have. Is it a single purpose, single throw relay that’s that’s normally open? We power and it closes. Or is it a single purpose dual throw relay that has two sets of contacts, one which is always open, one which is always closed in it’s normal state, and then just kind of reverses those two contacts when we energize the relay.
So normally open means if I don’t have power going to it, that contact is open, between common and normally open. And then if I do have power going to it, common and normally open then closes. My normally closed terminal is common and normally closed is normally closed, if I’m unpowered. Once I power that circuit, common and normally closed opens. So in its normal unpowered state, normally open is open, normally closed is closed And then once I power it, I reverse that, so I open or close.
In the HVAC industry, relays have really one purpose and that’s control and or isolation. In most cases it’s control. But that control is a form of isolation. So when I’m looking at my relays, understanding how they work, understanding how to use them, I can build some custom controls for temporary purposes to get parts ordered. Understanding how they work makes me a lot more effective at figuring out where my equipment’s not working. Those relays are in everything. They start at the thermostat, and from the thermostat to the zone panel, there’s a whole bunch of relays in there. From the zone panel to the HVAC equipment, there’s a whole bunch more relays, and closed contacts, and switches in that circuit.
A relay in action: we have two power sources. We’ve got two transformers. Maybe one of them is a low voltage circuit and the other is a high voltage circuit, and I want to switch the high voltage circuit based on the low voltage circuit. So fan motors, our vent motor, our compressor in the outdoor unit, the fan motor itself in the air handler. Those are high voltage circuits that are controlled with a low voltage input, and that low voltage input is driving a relay that makes and breaks the high voltage circuit. When I apply power to the coil side of my relay, my contacts are opened or closed, so once I apply power to it, my contacts are closed, I now allow the load, or in this case the light bulb in the diagram, I allow that to have power, that then flows to ground, energizing my load circuit.
So a relay is isolation. It’s control. I can use dissimilar voltages. In this case, I’ve got a 24-volt control of a 120-volt light bulb. That’s really how every single furnace operates. I’ve got a low voltage control that drives my fan motor, making it run in high voltage. I have a low voltage control that drives my vent motor, so low voltage control operating a high voltage circuit. My outdoor unit, my compressor. I have a contactor. The contactor makes and brakes a 220-volt circuit. So it’s all understanding where voltage applied closes a set of contacts and allows the circuit to continue operating.
What’s the best way to test a set of relay contacts? The best way to test to be 100% correct as far as whether or not that relay is working is going to be with an ohm test, a resistance test. When we do the ohms test that tells us the quality of our contacts. It tells us if we have an issue. Maybe our contacts are becoming burned or pitted, and that’s getting to be a problem for us. That’s going to restrict the electrical current. So, an ohm test is a foolproof way of determining if I have a good set of contacts.
