Hello, 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. Thoughts? Thanks! Mike

I have an ICP furnace Model NTG9075FGA3. When power is turned on to the furnace the exhaust motor/fan begins to run. After a few seconds I hear the Honeywell gas valve click. Then the furnace pilot lights. Then after a few seconds I should hear the main burner ignite. It does not always do this stage. When this happens, the blower motor circulates unconditioned air through the house on an infinite basis, and the temperature falls to ridiculous levels. Even when the main burner does light, it only provides heat for a short amount of time before going out, or being put out by the furnace. The fan continues to circulate now unconditioned air through the house when this happens. Over the last several years it's performance has been spotty, until last year I noticed it was blowing cold air. We got through the winter by resetting power to the furnace until it would light, then letting it run, then resetting power again when the main burner would go out. The time has come to decide whether I want to replace it for this winter or attempt to troubleshoot it.