18-Apr-2022

Intermittent Faults On Hvac Units! Fixing Ac, Heat Pumps, Air Handlers, Furnaces!

This is Craig migliaccio from AEC service tech. And today, what we're going over are what are the causes of intermittent problems when servicing HVAC equipment, such as air handlers heat, pumps, air conditioning systems or gas furnaces here, we're looking on the inside of an air handler equipped with electric strip heating and the cause of intermittent problems on heat pumps and air conditioning systems. Air handlers are due to a high electrical resistance across contacts or sections of wire where it's. Not always allowing the full amount of power going through the wiring or contacts. So in this case, we have a little relay right here. And I don't know if you can see right here, these little contacts, so there could be high electrical resistance on these contacts right here and that's what's inside this black box.

So this black box, um is housing. The contacts for the blower motor. And the blower motor down here.

This blower motor is going to be drawing a lot of current anytime that it's running. And so. That current is getting drawn across these contacts right here.

And so this is one example of one problem that you may have. And so another example is out at the outdoor unit. You have a contactor, and you could have pitting on the contacts right here. So this is, uh, basically, what's going to be powering the compressor and the outdoor fan motor and so there's a lot of current going across these contacts. And so when this sucks down, it may not be actually allowing the full amount of power going through. From here to here.

And so this is once again at the outdoor unit, here's, another example, these temperature sensors on the inside, uh, there is this contact right here and then there's a little tiny rod on the inside. So when this bi-metal disc pops due to heat, and it flexes, uh, right on these contacts. These contacts are so small any current going across them as you can see right here.

This switch in this switch is going to have a lot of current crossing it when the electric strip heaters are running. So. Back here are the electric strip heaters. And so those tiny little contacts could become pitted and then sometimes work and not work other times, depending on if it closes properly as far as the thermostat wire, you want to have a rubber insert over here on the side where the thermostat wires are coming through at they could become chafed right there. And so you could have thermostat wire that looks like this and so that's chafed thermostat wire. And that could also be the result of maybe a mouse. Or possibly a weed whacker outside.

And so that could be a problem. So you want to wiggle the thermostat wire while possibly the system you're trying to get the system to operate to see if there's a issue there, if you have wire nuts, especially if they're exposed outside, you know, they could be rusted. And there could be high electrical resistance in the wire nuts. You could have thermostat wire like this that's squished in the building with a staple that could be a issue. You could also have your. Thermostat could have low batteries. And so if it has low batteries, sometimes it's going to turn air conditioning on, and sometimes it's, not or heat to turn on, and it all has to do with the amount of power that the batteries have at that point in time and that's, if you're not using power from the HVAC equipment.

So you got to make sure to replace these batteries at least once a year, but maybe twice a year and use a good quality battery when you're dealing with the intermittent issue. There's, two. Things that you want to keep in mind and one is with the power off, you want to check all the electrical connections. And so the issue is, if you don't know where to look for the problem, if you know you have to basically divide the air handler into one is the high voltage loads. And the other is the control voltage.

And so you don't know, possibly where the issue lies at you do definitely want to do something. And I've I've seen some service techs kind of go out to a job three, four times. Without even checking the thermostat wire connection.

So these wire nuts making sure that they're tight you could have had somebody cut into this and kind of scar the wire due to a bad wire stripping process. And you can have high electrical resistance right there. So it's, checking all this thermostat wiring right here and making sure you have your fresh batteries and everything in your thermostat. And so what you could do is after, you know, you turn the power off you're, checking all. These electrical connections.

And if you find something that's loose, say, it's, your g, wire for your fan right here. What you could do is you can crimp this back down again. This is especially true with the outdoor unit because there could be some corrosion there. But anyway, once you have all those connections that are good. You could with the power off disconnect. The high current loads, such as the electric strip heating, and even the blower motor.

And you can check electrical resistance across. Contacts such as these right here. So you can check right here to see if you have very close to 0.0 ohms of electrical resistance. You can see we have 0.0 right now. So if you had one ohm of electrical resistance that would mean that your voltage is going to drop across here, while it's drawing electrical current, while the electric strip heater is running, and that could be an indication of a bad electrical contact. Likewise, over here you right now we should have very close to 0.0 ohms across the.

Contacts than normally closed contacts, but then what's going to happen is when the air handler is running the contact between here. And here should be closed. So you could check this with a voltage across from here to here or across a switch, so there's, multiple different ways in order to check switches, and you can check out another video. I have on measuring electrical switches furnaces are a little different from air handlers as far as what the intermittent problem could be. You could have the same.

Type of thing you could have a high electrical resistance issue, either with thermostat wires or your high voltage wiring or your connection, or your contacts, that's that's. Certainly one thing. Another thing on a gas furnace is that you could have a issue with water from the flame process. So you could have either water in your exhaust pipe. And if your pipe is not pitched properly, it could be full of water and what's going to happen is it's going to mess up the pressure reading on the the.

Pressure switch, you could also have your condensate trap. Now, this is one of the most common things that you could have as far as the intermittent issue, where the trap gets sometimes clogged and then it is then drains slowly. And then all of a sudden you are able to have your pressure, um being red at your pressure switch that the proper pressure. And so you need to make sure to either blow out or vacuum out these condensate traps, every once in a while, and you need to clean them out, you got to.

Make sure that you have proper pitch for your exhaust pipe about a quarter inch, pitch per foot going away from the furnace, you also have other types of condensate traps. You can't see into. And so you need to make sure to vacuum or blow them out. And so you want to make sure to disconnect from the pressure switch when you're cleaning out your trap. And so I have another video linked down in the description section below on how to do that as far as seeing this pressure problem. You want to have a. High quality manometer, you want to have a t fitting so that you can get in between this tube and the pressure switch.

And then you can compare your pressure reading to what it's listed at on this little rating right here where you can look up the pressure switch online. And I have another video for testing pressure switches that link down the description section below. And the third major thing that happens on furnaces as far as the intermittent issue is the flame proving process that's. Occurring over here in the combustion chamber. So in this case, there is a smart valve right here. And so you have a little, uh pilot, right here. And the pilot is what needs to be proven as far as there being a flame.

And so you have this little tiny flame rod right here. And so this flame rod could be corroded on other furnaces. You have a larger flame rod such as this right here. And this is a direct ignition. So it's, igniting, the burners, and then the flame has to travel across over to this side, where. There is a flame rod there's constantly voltage on this flame rod and what's happening is the flame rectification process is occurring where there's a flame going from the burner retention head right here past this flame rod, and you have the power basically getting rectified, and then you're going to see a direct current it's, a micro amp signal on the ground right here, and then it's a matter of having a good ground on your furnace. And so I have other videos on flame notification down in the.

Description section below, but basically, uh on this one this. This section of wiring right here could be changed out for your smart valve from here over to here. And this little pilot tube a lot of times with the pilot ignition a lot of times.

This is your ground. And so you got to make sure that this is snug and tight and not corroded on other furnaces. You want to make sure that you have a good ground wire from your combustion box down to your control board at least with a gas furnace. You.

Have a status code light on the control board for furnaces that are said, 20 years old or newer, and that at least gives you a place to start. Now, if that status code light is not flashing, an error code, it's, very likely that your intermittent problem has to do with the thermostat wiring or the thermostat, possibly the control board. If your LED status code, light is flashing. A lot of times it's going to be something that has to do with water and pressure, such as your pressure switch, checking the. Pressure of the inducer motor or a limit circuit fault, such as uh contacts on the thermal limit switches. And you know, you could have a flame roll out issue over here and an ignition proving failure. So you could have a issue with the background, going all the way back to the breaker box.

You could have a background from the control board up to the combustion box, or you could have a dirty flame sensor or something like that. So at least this gives you a place to start at. And it kind of gives you. The direction, hey, I need to get my manometer out and check my water column of pressure or hey, I need to check my limit circuits and see if I have voltage drop across each of the thermal limit switches, or I need to check for flame rectification or to turn the power off to the furnace and clean that flame rod that could be a thing, or it could even be at the burner. Retention, head itself, maybe it's just completely rusted, and it's, not providing a good metal surface for the flame rectification. Process to occur and for the board to verify that there is a flame. So when it comes to intermittent problems with HVAC equipment, the rule is you got to make sure to do something.

So if that means, if you have no leads, possibly the building owner doesn't, tell you what's wrong. And you don't see any status codes flashing, you kind of need to cycle the system. Turn it off check the electrical connections. Crimp, the connections, uh, check the operation. You know, all of that type of thing you want to have a good. Multimeter, and you want to have a good water clinometer with a t for furnaces, if you want to learn more about troubleshooting the specific components identified in this video, I have links to many videos down in the description section below on the thermostat wiring and the thermal limit sensors and flame rectification and the pressure switch.

So make sure to check all those out and make sure to also check the articles that we have over our website at aecservicetech.com. So hope you enjoyed. Yourself we'll, see you next time at ac service tech channel.