Anyone good with the HVAC?

[Missourian]

if that's the sch for your unit look for 24vac on terminals 4 and 6 (blue and white) in the 9 pin connector to the elements. The relay is probably a black plastic box near the elements. They could be burned out or the temp limit could be bad. Don't confuse the 240 volt wiring for the 24 volt control wires unless you are comfortable with that. There should be a 7 second time delay from when the fan starts to power the strip heaters, if not the blower time delay relay may be bad.

I'm pretty sure this is the relay.

the single red @ left rear is 27v

Two reds @ right rear are 119

Purple black @ right front 119

Light blues at front left are 0

This is with the red 27v to the thermostat jumped to the white from the thermostat.

 

[Grumblenuts]

Checking the relay contacts for corrosion is a part of normal annual maintenance. I've had that problem already. Since my circulator crapped out two years ago I've just been burning wood and pellets. Simpler stupider. Oh, you have an HVAC unit, that's right. Never mind

 

[Grumblenuts]

I'm pretty sure this is the relay.

View attachment 758299the single red @ left rear is 27v

Two reds @ right rear are 119

Purple black @ right front 119

Light blues at front left are 0

This is with the red 27v to the thermostat jumped to the white from the thermostat.

That looks like a transformer.

 

[Missourian]

if that's the sch for your unit look for 24vac on terminals 4 and 6 (blue and white) in the 9 pin connector to the elements. The relay is probably a black plastic box near the elements. They could be burned out or the temp limit could be bad. Don't confuse the 240 volt wiring for the 24 volt control wires unless you are comfortable with that. There should be a 7 second time delay from when the fan starts to power the strip heaters, if not the blower time delay relay may be bad.

Jumping red to green I get a little more than 7 seconds...so that's gtg.

 

[Missourian]

That looks like a transformer.

Could be.

Here is what I'm working with.

Not my area of expertise by a long shot.

I'll go get a better picture.

That might be the step down transformer to get to 27v.

 

[Missourian]

Relay?

 

[Missourian]

Checking the relay contacts for corrosion is a part of normal annual maintenance. I've had that problem already. Since my circulator crapped out two years ago I've just been burning wood and pellets. Simpler stupider. Oh, you have an HVAC unit, that's right. Never mind

We have four layers of redundancy in heating, so we're not hurting.

Plus it isn't that cold here.

The wood stove is keeping things toasty...so it's not an emergency.

If push comes to shove, I'll call an expert on monday.

 

[Grumblenuts]

Yep, relay at the top there.

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[Missourian]

the watcher
Grumblenuts
toobfreak

The relay appears to be working.

With the white and red jumpered...

The white goes into one side of the relay. I can't reach it because it is on the backside...but going in it is at 28 volts.

Light blue it on the opposite side in the same location. Pretty sure it is the common.

238 goes in from the right side...119 in each of two male blades.

119 comes out the left side three times in three male blades...there is likely a fourth that I cannot see.

When the jumper is removed...there is the telltale solenoid click in the relay as the 27v to the white wire is removed.

There is then no power on the left side of the relay.


Still no heat.

And the fan still activates immediatly after the red to white jumper is applied with the green (fan) wire disconnected.

Tomorrow I'll test the continuity of the thermocouples at the coil connections.

..unless y'all have any ideas.

 

[sparky]

the watcher
Grumblenuts
toobfreak

The relay appears to be working.

With the white and red jumpered...

The white goes into one side of the relay. I can't reach it because it is on the backside...but going in it is at 28 volts.

Light blue it on the opposite side in the same location. Pretty sure it is the common.

238 goes in from the right side...119 in each of two male blades.

119 comes out the left side three times in three male blades...there is likely a fourth that I cannot see.

When the jumper is removed...there is the telltale solenoid click in the relay as the 27v to the white wire is removed.

There is then no power on the left side of the relay.


Still no heat.

And the fan still activates immediatly after the red to white jumper is applied with the green (fan) wire disconnected.

Tomorrow I'll test the continuity of the thermocouples at the coil connections.

..unless y'all have any ideas.

Missourian , can you meter the actual heating coils ? 240V across the leads to it? ~S~

 

[Grumblenuts]

Yep, if you can cut the power, just check that HV coil for continuity. Otherwise, it's probably not a relay problem unless a contact is loose or dirty which doesn't appear likely. Sparky to the rescue..

 

[toobfreak]

The relay appears to be working.

You understand that the low side (24V) activates a relay inside which pulls closed the high side (220VAC) starting the heat coil.

Light blue it on the opposite side in the same location. Pretty sure it is the common.

It should probably say COM on the controller box. If so, then you should have continuity between that point and either circuit or earth ground.

When the jumper is removed...there is the telltale solenoid click in the relay as the 27v to the white wire is removed.

Offhand, it sounds like it is working then. I'd expect then you would have continuity on the high side when the switch is closed. Do you?.

There is then no power on the left side of the relay.

Should there be? And if so, then where is the power?

Still no heat.
Tomorrow I'll test the continuity of the thermocouples at the coil connections.

I don't own an electric furnace and its rather hard to troubleshoot not actually BEING THERE, but offhand, I'd start at the heater element and work back (you might want to kill the AC unless you're sure you are safe) looking for continuity in the circuit and eliminating each piece of the circuit one by one and keep eliminating causes until you can narrow down more where the problem is. If you have an ohmmeter that can operate in the presence of voltages (like a Fluke 27), that is particular nice, but most ohmmeters don't like that.

 

[toobfreak]

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[Missourian]

Missourian , can you meter the actual heating coils ? 240V across the leads to it? ~S~

Maaaaaybe.

Everything is in the way...but I ordered some extra long multimeter probes that I might be able to sneek back there...

Won't be here until Monday though.

 

[Missourian]

You understand that the low side (24V) activates a relay inside which pulls closed the high side (220VAC) starting the heat coil.


It should probably say COM on the controller box. If so, then you should have continuity between that point and either circuit or earth ground.


Offhand, it sounds like it is working then. I'd expect then you would have continuity on the high side when the switch is closed. Do you?.


Should there be? And if so, then where is the power?


I don't own an electric furnace and its rather hard to troubleshoot not actually BEING THERE, but offhand, I'd start at the heater element and work back (you might want to kill the AC unless you're sure you are safe) looking for continuity in the circuit and eliminating each piece of the circuit one by one and keep eliminating causes until you can narrow down more where the problem is. If you have an ohmmeter that can operate in the presence of voltages (like a Fluke 27), that is particular nice, but most ohmmeters don't like that.

The coil or the thermocouples are probably the problem.

I'm just working my way though it.

The white wire shouldn't activate the fan...but it does. That's just weird.

I was hoping someone had seen something similar.

I can pull everything apart tomorrow want check the coil continuity and the thermocouple continuity...but the integrated circuit breakers are the first things to come out... Which means either I'll lose the power input, or have it hanging out exposed... Which never tickles my fancy.

But every without power I can test a lot.

So we'll see.

 

[Grumblenuts]

 

[toobfreak]

The coil or the thermocouples are probably the problem.

That would seem to ally with the article I linked above. Good luck.

 

[Grumblenuts]

I see the two relays now. They look plenty beefy, so other than spraying the contact areas with cleaner, I'd just make sure none of the wire junctions are loose by jiggling them each gently with a stick and see if anything kicks.

The toobman is correct in that those relays simply close HV circuit contacts. There are no HV "coils" involved there. I was really thinking about the high side of that white transformer where you were to begin with.

Then there would be heating elements, but that's not something apt to go all of a sudden, particularly in multiples. "Thermocouples" same. Thermocouple maybe. More likely to be in the control area you're looking right at. Fuses, breakers, bad connections, wires, discolored catalytic capacitors, resistors, diodes, transistors if you can see any of those.. but doesn't look that complex from the diagram.

The white wire shouldn't activate the fan...but it does. That's just weird.

It is. I recall having a similar issue many years ago which turned out to be just a contact problem contained within the main thermostat itself. It was just too fancy for its own good. New thermostat and done.

 

[sparky]

I'd start at the heater element and work back

yes, if the t-stat works & coil pulls in, blower works etc , which appears the case

If you have an ohmmeter that can operate in the presence of voltages (like a Fluke 27)

exactly why i own one

I can pull everything apart tomorrow want check the coil continuity and the thermocouple continuity.

meaning the actual heating coil element in the unit ? continuity may be somewhat problematic due to high R , but if you do get 238V to it and it's not heating (drawing power) it would be indicative of a burnt out one. ~S~

 

[toobfreak]

meaning the actual heating coil element in the unit ? continuity may be somewhat problematic due to high R , but if you do get 238V to it and it's not heating (drawing power) it would be indicative of a burnt out one.

Worth mentioning is that so long as the heating element is connected to the circuit, continuity or ohmage measurements there are likely worthless or at best misleading in testing the state of the actual element as even if open, the meter then would simply read the resistance of the circuitry upstream behind it, whatever that is and may still appear good to the meter.

Short of disconnecting one side of the element which may be hard to do without really getting in there as these are meant to carry a high current, if these are difficult to reach in order to check if voltage is present (which would only be high / 220VAC if the element is open anyway I would think), you might get a couple of long wood or plastic sticks and tape the test probes to them to give yourself better and safer reach to probe around.