Rheem Classic 90 Plus Not Working

Old 10-11-14, 02:39 PM
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Rheem Classic 90 Plus Not Working


I have an issue I've tried troubleshooting on my own and reading some other threads here, but decided to just post myself (and someone recommended I do that anyway in another thread).

I have a Rheem Classic 90 Plus gas furnace, about 6 years old. It just "quit" one day. Here are the symptoms and what I've checked so far.

1. Thermostat "clicks" when it gets to the right temp.

2. I hear an electrical hummm start in the furnace, then it quits after about 30 seconds.

3. I read some basic troubleshooting info online, so I checked the LEDs during this process. Normally the OK light and the PWR light are on solid. When the hummm starts, the OK light flashes twice periodically.

4. The troubleshooting sheet inside the furnace door indicates 2 blinks means PS problem (pressure switch) and to go to block F on the flowchart.

5. Block F has a variety of things to check. I did the following.

5a. Removed the vacuum tube between the PS and the induction draft motor (IDM). No moisture or debris, and I blew air at it and it felt like the flow was the same.

5b. Did the same with the vacuum tube between a second PS (I guess?) and the burner chamber (I think?) and it also seemed fine.

5c. It says if I have a downflow furnace, to check the aux limit switch. How can I tell if I have an upflow or downflow furnace? And, I didn't see any other switches in there but I'm not really sure what I'm looking for.

5d. Says to check the vent for blockage. I'm not positive which vent it's talking about. I think it means the one that comes from the IDM and leads to the outside venting. I didn't feel comfortable checking that -- on my unit, it's a hard black plastic that seems rather firmly attached to the IDM output, and it leads directly into a large white PVC pipe that leads up into my attic and I assume outside. It didn't look easy to get off, assuming that's what it wants me to check.

5e. I don't know which part/where the condensate tube is. I think it might be a thick black rubber hose coming from the bottom of (what I think is) the vent. It also looks secure and hard to remove.

6. I did the ol' "turn off the power and gas, turn off the furnace on/off switch, wait 5 minutes and turn it all back on" reset thing, twice. No change.

7. I saw in another thread someone asked if the IDM was getting hot, so I got out my little temp gun and checked. The attic and rest of the furnace components are 64F right now, and the IDM is 98F after trying to turn it on. Not sure if that qualifies as "hot" or if that's just normal when it's ready to run. I'm not sure it's running -- it has that electrical humming sound, but I don't think it's actually spinning.


Old 10-11-14, 05:25 PM
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Welcome to the forums.

If you just hear a hum and not the sound of a fan then the induced draft motor is more than likely defective. They're pretty loud when they're running.

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