Random malfunction on Rheem furnace.

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BuzzLOL

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I didn't hear the gas valve click (and yes, the gas is turned on). However, the ladder schematic shows, that between the pressure switch and gas valve pins, are 2 open switches labeled "K1".
I would expect those are temperature limiting switches on the side of the air ductwork... might be sticking switch or lose connection. My furnace installer rewires so that the inducer fan and igniter are also prevented from working if those switches not 'happy'... ...
 

Guzzle

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The spark ignitor sparks a couple times. . .and then everything shuts down. There are no error codes.
>Something seems to have timed out. How long between the sparks & the shut down?

I didn't hear the gas valve click
>No, because the unit thinks it will not have ignition. This furnace will not blow up your house any time soon.

I try it again and check for 24v at the gas valve. I only get 1v.
>Could be a spurious [not Phantom] voltage. I guess I’d count 16v & above as “on” and 8v & below as “off”.
What meter are you using?

labeled "K1".
>A relay, maybe 1 cubic inch in volume.
You could actually draw several schematics depending on which relays are closed or open. Tedious PITA.

That would appear to be where I'm losing my 24v.
>if the relay coil energizes, the contacts may be bad.
More that 100 millivolts across closed relay contacts [when carrying rated current] mean bad contacts, high contact resistance, worn contacts caused by arcing caused by switching inductive loads [coils].

As of right now, bad contacts are my numero uno guess.



By now, Mr. Holmes, your furnace knows you are not letting this go. It should be scared! :D
 
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Eddie_T

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You can check the gas valve by disconnecting its leads and temporarily jumpering from 24v transformer listening for click and gas flow.
 

Guzzle

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He seemed to indicate that the sparker and gas valve were good
You can check the gas valve by disconnecting its leads and temporarily jumpering from 24v transformer listening for click and gas flow.
Yes, the valve could be intermittently sticking closed. Maybe the internals are gummy.

This may account for no bad voltage readings & no codes. The control board would need to monitor a flowmeter to check for no gas delivery. It's more concerned about gas delivery when "no spark".

When the symptom shows up again, I'd try whacking the valve firmly with a screwdriver shaft several times while sparking.

Another way would be to "jump start" it with 48vac. You could wire two 24v 'formers in series, phased properly to deliver 48v, & then whack the valve with that & listen for the click.
Disconnect the valve wires first so you don't feed current back into the furnace. You are doing this independent of the furnace wiring.
Then sell one trans on e-bay.
 
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kok328

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I have not yet actually seen it try to light, but the repair tech did. He seemed to indicate that the sparker and gas valve were good, but something else was interrupting the ignition sequence. Also, he said the furnace is supposed to try to light 3 times before going into lockdown. But mine is shutting down after the first failed attempt.

The furnace worked this morning so I couldn't do any further troubleshooting.
The tech is correct about the 3 attempt lockout. so if your is locking out on the first try then it is the control board causing that.
I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp.
Have any of the techs checked gas pressure at the valve?
 

Guzzle

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I don't believe 24v goes to the gas valve
Mine does, to 3 coils. I also ohm-ed out the coils.
By now I have a whole notebook on my ancient furnace.

But IIRC there are valves that work on 28 mV & 750 mV.

BTW, at least one tech we had did not know what a SPST switch is. They just replace modules. Maybe the company CEO had schooling, the rest maybe learned by OJT.
Goodheart-Willcox publish books on this.

We have got to be close by now. There's hardly anything left that can cause this.

Re: 28 mV
Table 4 on page 7 implies that the slightest resistance in the circuit, or tarnished wire, can prevent proper operation.
The valve coil resistance may be 15 milliohms, so at 28mV you'd get almost 2A, enough to move a solenoid armature. A clamp-on ammeter may work at these low circuit resistance levels.
 
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Eddie_T

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I guess an easy check might be to unplug the wires to the gas valve and probe them during the turn on try to see if momentary (prolly several seconds) voltage is present during the turn-on attempt.

edit: On second thoughts, since it's intermittent this may only help if it's not present. However if present it will confirm that it's 24v. A clamp ammeter would be better.
 
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Raindem

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Thanks for the replies. I'll try to address all the points that were brought up.

IIRC K is used to designate a relay.
On the circuit board? Or this a relay integrated with the gas valve? Is that the same as a solenoid?

I would expect those are temperature limiting switches on the side of the air ductwork... might be sticking switch or lose connection.
If that's the same as the hi-limit switch, the schematic is showing it separate from the K1 switches

Something seems to have timed out. How long between the sparks & the shut down?
Just a second or two

What meter are you using?
A Fluke DVM. But it doesn't have a current clamp so I can't do the amp draw tests.

As of right now, bad contacts are my numero uno guess.
Which contacts?

You can check the gas valve by disconnecting its leads and temporarily jumpering from 24v transformer listening for click and gas flow.
I thought about doing this. Later on in the afternoon the furnace started working again, and I wanted to get back up there and see what the gas valve voltage was, for comparison purposes. But I didn't have time to do that. Maybe tomorrow I can get that value while the furnace is running.

When the symptom shows up again, I'd try whacking the valve firmly with a screwdriver shaft several times while sparking.
Already tried that.

Another way would be to "jump start" it with 48vac. You could wire two 24v 'formers in series, phased properly to deliver 48v, & then whack the valve with that & listen for the click.
Not really comfortable trying this. I'd lean more towards just replacing it if it is suspect. But I want to nail this voltage thing down first.

The tech is correct about the 3 attempt lockout. so if your is locking out on the first try then it is the control board causing that.
I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp.
Have any of the techs checked gas pressure at the valve?
I guess I'm misreading the schematic. It looked like the gas valve was supposed to be getting 24v. None of the techs tested for pressure at the gas valve.

I guess an easy check might be to unplug the wires to the gas valve and probe them during the turn on try to see if momentary (prolly several seconds) voltage is present during the turn-on attempt.
I'll try that tomorrow. Should the meter probes go into each wire, or should I be using another common?
 

Guzzle

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IIRC K is used to designate a relay.
On the circuit board? Or this a relay integrated with the gas valve? Is that the same as a solenoid?
>>My two 1 cu in relays are mounted on the board. A massive relay may be mounted on the furnace metal.

A relay
-controlled by the control board supplies current to the gas valve.
-uses a coil to pull in a spring-loaded hinged armature which does the switching of a current too heavy to be handled by the control board.
There are also solid state relays (SSRs). Pull up some pictures on Google Images.

A solenoid uses a coil to move a spring-loaded cylinder-shaped slug over some distance.


Something seems to have timed out. How long between the sparks & the shut down?
Just a second or two.
>>Don't know what responds this fast.

A Fluke DVM. But it doesn't have a current clamp so I can't do the amp draw tests.
>>OK.

Which contacts?
>>the relay contacts & this guess is now tied with the gas valve being gummed.

>>If the valve is gummed, I’d say 24v for one minute or 48v for one or two seconds should give you a click.

I guess I'm misreading the schematic. It looked like the gas valve was supposed to be getting 24v. None of the techs tested for pressure at the gas valve.
>>When it’s working, check the voltages on the gas valve, one terminal to the other & all terminals with respect to ground. With three gas terminals this is 6 measurements.
Also measure all the ohms. The current into the valve will be slightly less than the valve volts/valve ohms. I=E/R.

 
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maxdad118

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I don’t think it’s a bad board, gas control. Maybe try checking for bad/loose connections. I do a fair amount of furnace troubleshooting in my line of work, although I’m not a licensed hvac contractor. It’s intermittent and random, it appears, correct? Was the pilot actually cleaned? Do you have a lazy pilot? If the pilot orifice isn’t clean/clear it may spark but the gas isn’t getting to the spark. I would try manually lighting the pilot hood(where the gas comes out) while it’s sparking to see if it lights.
 

Eddie_T

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There won't be a pilot if it's a spark or glow plug igniter.

It might be worth checking youtube to see if there are any trouble-shooting postings for your particular furnace or a similar model.
 

Guzzle

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Mr. Raindem, you're closer to this than we are.
Can you summarize for us
what's been tried, how often & the outcome &
what's left to reasonably try?

BTW, you seemed to have posted your AC schematic. We need the other one.
 

BuzzLOL

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"I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp." -kok328

My gas valve says 24 volts on it...

"But IIRC there are valves that work on 28 mV & 750 mV." -Guzzle

Those low voltages/currents come from a thermocouple... such as on older hot water tanks... on a newer furnace, they would probably signal the computer...

"There won't be a pilot if it's a spark or glow plug igniter." -Eddie_T

On my furnace, the spark ignites a little pilot flame, then it spreads out to the 4 burners... gas valve has pilot and main solenoids...

"If that's the same as the hi-limit switch, the schematic is showing it separate from the K1 switches" -Raindem

My furnace has more than one set of temperature switches in that location...
 

Raindem

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Another day troubleshooting. When I woke up this morning the furnace wasn't working. When I checked it a couple hours later it was, so I went up to check more voltages. The gas valve voltage is the same as when it was not working, so that's not the problem. BTW, I misread the multimeter. It's not 1v, it's 0.1v. I disconnected the blue wire and checked voltage when it tried to start and I was getting 15v there, which is what someone was saying I should get. Curiously, as I was checking voltages, the furnace stopped working. I checked the gas valve & wire voltages again and the same as when working. Looking again at the red light on the circuit board, it glows solid red when first trying to start up the furnace. When the furnace shuts down after the brief spark, the light goes out completely and won't come back on until I reset power. Don't know if that is important, but I thought I'd throw it out there.

In response to today's comments...

When it’s working, check the voltages on the gas valve, one terminal to the other & all terminals with respect to ground. With three gas terminals this is 6 measurements.
Did that this morning. Blue wire to common was around 0.1v. My GV only has 2 contacts. One contact to the other was around .05v, but the meter kept jumping around.

Also measure all the ohms. The current into the valve will be slightly less than the valve volts/valve ohms. I=E/R.
I'm not that electrically literate. You'll have to specify which wires or connections I need to check.

Don't know what responds this fast
Me neither. I've watched literarally 30 videos on troubleshooting furnaces (including the one you posted). None of their examples of bad pressure switches, gas valves, hi limit switches, etc, match what my furnace is doing. It literally sparks for a split second and then shuts down.

Maybe try checking for bad/loose connections. I do a fair amount of furnace troubleshooting in my line of work, although I’m not a licensed hvac contractor. It’s intermittent and random, it appears, correct? Was the pilot actually cleaned?
Connections have all been checked. Sparker, Flame sensor, hi limit and flame rollout contacts have all been cleaned. Connections to circuit board have been pulled off and reinstalled. No pilot light on this furnace. Just the sparker.

It might be worth checking youtube to see if there are any trouble-shooting postings for your particular furnace or a similar model.
None that I could find. And I think by now I've viewed every video ever made on furnace troubleshooting ;)

BTW, you seemed to have posted your AC schematic. We need the other one.
It included the circuit board connections for the gas, But that's irrelevant now. I've attached the rest of the schematic. Hope you can read it. My old eyes have trouble.

Again, appreciate all the help on this. But it is getting frustrating beyond belief. This problem started last winter. After the first tech couldn't fix it, the weather turned warm and we didn't worry about it until this year. I have a feeling this winter will end also without any resolution. In fact, they'll probably cure COVID before I ever get this furnace fixed. I can't afford $8k a new furnace right now so we'll have to get by with electric space heaters all over the place.

Schematic.JPG
 

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Guzzle

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Curiously, as I was checking voltages, the furnace stopped working.
Hopeful, not curious to me.
You mechanically disturbed something that was loose.
You now may be able to reproduce the fault whenever you want to if you can retrace your steps.
You are close. Connections that are supposed to be insensitive to the pressure of your test prod at sensitive. If these connections are soldered I'd say it's a solder joint that has become bad.

Or a coincidence, not hopeful.

With 15v, your 40VA transformer [24v @ 1.67A, less voltage at heavier current] may be slightly overloaded. I'd try to find where all the amps are going.

More to say later.
 

BuzzLOL

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I was getting 15v there
I just turned my furnace on, didn't disconnect anything, reading 25.5 volts AC at the gas valve terminal... between '24 volt' white neutral wire screw and black hot wire screw... maybe your 24 volt transformer has about had it... or maybe a weak connection somewhere's...
I replaced my old 16 volt door bell transformer when it wouldn't ring the doorbell any more...
BTW, I don't think the 24 volt wiring gets connected to ground/furnace metal, both wires an isolated circuit...
 
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