Random malfunction on Rheem furnace.

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Raindem

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Hello. I have a 10 year old 5-ton Rheem Classic combo unit. For the past couple of years I've dealt with an intermittent no-heat situation.

Here's what it does. In the morning, when the heat is supposed to turn on, the inducer will start and the the spark igniter will click a couple of times, then it shuts down and won't retry until power is reset. The burners never actually light. There are no error codes. At some point later in the day, late morning or early afternoon, the furnace will start working normally. At that point it will function for the rest of the day, until the following morning. Some days it works all day. Other days it doesn't work at all. But most days it does this "not work in the morning but work in the afternoon thing". I kept a log of outside temperatures and humidity to see if there was a pattern, but I did not see one.

I've had two different HVAC repairmen out on 5 different occasions but no one can diagnose it. Sometimes the furnace starts working before they get here, and it's a wasted trip. But sometimes it doesn't and they are able to go through the troubleshooting sequence. They've tried bypassing the thermostat, cleaning the flame sesnor and spark igniter, replacing the circuit board, and replacing various sensors (even though there were no error codes). Blower works fine when directly activated (by thermostat or jumping wires). They report that voltage is normal at all the key locations. The filters are new. I hate to keep throwing parts at it and paying for service calls when no one seems to know exactly what the problem is. I've tried to troubleshoot it myself also, being that I'm in a position to head up to the roof immediately when it is not working. I have my tool bag on standby in the morning ;)

So I'm posting this in the hopes that someone else has encountered this same thing and has an idea on what to look for. Thanks.

Curt
 
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Guzzle

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Hooking up a 4 or 8 channel analog datalogger or event recorder will probably nail it in one session, if you can rent/buy such a thing.
It will trigger on the fault & display the sequence of events immediately preceding the fault, as if you are looking back in time.

Post a schematic if you can.

Car dealerships have these to track down intermittent problems for their favorite customers.
 

Guzzle

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Electronic Hobbyist websites may be able to point you to a no-name garage outfit that sells dataloggers, perhaps in kit form.

A block diagram for it could be analog to digital convertors feeding a memory chip along with a clock pulse generator & various "glue logic," possibly powered by a wall wart.
 

Raindem

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Thanks for the replies. But I have no idea what you're talking about.
 

Guzzle

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Search on "event recorder" or "datalogger".

It does seem that the techs did whatever they could & even if their bosses came out, they wouldn't figure it out either.

And it may be something as simple as a loose connection. Connections are as much a component as the other parts.

Maybe an HVAC guy will chime in on how these problems are normally handled. My viewpoint is from an engineering standpoint.

You could gamble on replacing the control board.

What do you see as your options at this point, besides putting up with it?
 

Raindem

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The control board was already replaced. Of course that doesn't mean the new one can't be bad also. I was just hoping that someone else had already dealt with this, and could pass on the fix.
 

Guzzle

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There can't be too many faults this basic that you get no error code.

Maybe there is a Technical Service Bulletin out on this problem.
You could write the OEM, I wouldn't bother calling.
If I were the HVAC tech I would have contacted the OEM. You could ask the previous, now-disheartened techs if they did so.

I had an intermittent no-crank with my '89 Sentra so I wired LEDs to four crucial points & found the problem immediately, but you don't have the option of sitting in front of your furnace watching test points.

With my relay-logic no-computer no-LED 1982 furnace with this problem I'd think a single thing is failing intermittently, probably a loose or tarnished connection.
If tarnish, it could depend on relative humidity.
 
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Raindem

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I asked the last tech if it would be helpful to contact the manufacturer. He said something like "Yeah, I guess I could do that", but never heard back from him. I'll just keep going up there on mornings it doesn't work until the problem reveals itself, or summer arrives.
 

Guzzle

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If you really want to get their attention, write to the state agency that oversees these companies. Sometimes it works.

You have paid to get a furnace that is reliable. They can't now say that they don't know how to fix this.
 
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Guzzle

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In the morning, when the heat is supposed to turn on, the inducer will start and the the spark igniter will click a couple of times, then it shuts down and won't retry until power is reset. The burners never actually light. There are no error codes. At some point later in the day, late morning or early afternoon, the furnace will start working normally.
So you or some geek have a large interval of time where you can make three or four voltage readings to find out what state this furnace has latched itself into.

Prod the spade lugs on the components rather than disturbing the connectors.

If the fault clears while you are doing this, you are close.
 

Raindem

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Yesterday, the furnace wasn't working in the morning but I had other committments and couldn't check it out. By the time we got back home it was working. Today, I'm up bright and early ready to go troubleshooting, and it turns on exactly when it was supposed to.

This will take time.
 

Guzzle

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It will notify you when it fails. Have your test points & meter at the ready.

There is probably a schematic/wiring diagram/"ladder" diagram pasted on the inside of a pop-out panel, maybe in the air handler section.
 
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Eddie_T

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If the igniter tries a couple of times then it would seem that either there was either no spark or no gas.
 

Raindem

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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.
 

Guzzle

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It could well be a software bug & the OEM may decide to fix this if the OEM thinks it will come back again & again, to bite him/her self.
Probably S/W is off limits to most, if not all, techs.

I guess the OEM cannot say, "Suck it up.", at least not in writing.
 

BuzzLOL

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After about 20 years, a relay the installers added to my furnace to turn it on when the thermostat calls for heat got so it didn't work without a tap on it the first time I turned the furnace on in the Fall... then it was fine the rest of the winter... but that doesn't sound quite like your problem...
 

Raindem

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I was able to do some troubleshooting this morning since the heater was not working. So going back to the start...

It has 120v going in on L1 and L2. It has 24v coming out of the transformer and going to the circuit board. The thermostat has 24v going to it and, when the proper connections are made, is sending 24v back to the furnace circuit board. So power appears to be good. Filters are brand new.

At the furnace I jump the white to red thermostat wires to call for heat. The inducer kicks on. The pressure switch closes (I verified 24v going in and out when inducer running). The spark ignitor sparks a couple times (I checked it visually) and then everything shuts down. The burners do not light. There are no error codes.

I didn't hear the gas valve click (and yes, the gas is turned on). I try it again and check for 24v at the gas valve. I only get 1v. I trace the wire back to the circuit board connector and am only getting 1v there. According to the schematic, 24v goes from the pressure switch to the gas valve, and I verified 24v at the pressure switch pin on the same connector. However, the ladder schematic shows, that between the pressure switch and gas valve pins, are 2 open switches labeled "K1". That label is not in the notes or component codes. That would appear to be where I'm losing my 24v. Are those switches on the circuit board itself, or is there something else I can check? In the attached ladder diagram, the switches I'm asking about are in the lower left of the IFC (integrated furnace control) board.

Thanks
 

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