Need help troubleshooting Rheem RGDG

[l8krfan]

I have a Rheem RGDG-07EAUER. Yesterday I noticed that only cold air was coming out of the vents. Both the draft motor and the blower motor were running but no flame. Thermostat was on and set for heat. I turned furnace off then back on and same result. The igniter never even glowed so I jumped to the conclusion it was the igniter and replaced it. It is still doing the same thing. The weird thing is that even when the thermostat is set to off and the fan is set to auto, the draft motor and blower motor continue to run non stop. I let them go for about 20 minutes to see if they would turn off and they didn't. I do not have a manual for this furnace so I followed the Integrated Ignition And Blower Control troubleshooting guide on the IIBC cover. I got to the step where it asks if the igniter warms up and glows red - No. So it lists 1. Check for blocked vent - did not find anything. 2. check air proving switch (closed) - there was no air proving switch listed on the diagram but I read somewhere online that it is also known as the negative pressure control (silver disc with two leads attached and an orange hose running to the blower motor housing) Is this correct? If not how do I find it and how do I check it? It also had a side note that said:Inducer shuts off in 60 sec if air proving switch does not close. What is the inducer? No inducer listed on diagram. Just induced draft blower. 3. Check wiring to igniter - seemed good and secure 4. Check for 115V at igniter, terminals and at IIBC terminals - only about 1.6 or so at igniter. Same at IIBC terminals, but the terminals in the same wiring harness as the igniter that go to the draft motor read around 119V. I left the meter leads on the terminals for the igniter for about 2 minutes with no change. So it says with the no to the meter test to replace the IIBC. Is that what I should do next and is it something that I can do? I have access to a wholesale acct at a local HVAC supplier, does anyone know about how much it will cost me? Thanks in advance for any help. Times are tough right now and I can't really afford to pay someone to do it.

[HayZee518]

in the upper part of the hot exhaust is a disk with a copper colored tubing coming out of it and going into the exhaust ducting. this is the inducer switch. the inducer is the induced draft blower. what is the IIBC terminals for?

[l8krfan]

The IIBC terminals are where the wires that power the draft blower and the igniter attach to the IIBC or what I like to call the circuit board.

I still can't figure out what the "air proving switch" is.

[HayZee518]

I found this picture on another users thread. The air switch is the round metal "disk" with the copper tubing going into the exhaust stack. Two wires come off this and go to the circuit board. It's technically called a diaphragm switch.

[l8krfan]

So how do I test it to see if it is working? Or are you saying it is my problem and replace it? I have attached a couple of photos of my unit.

[HayZee518]

I saved your pictures. In the middle photo upper left round diaphragm unit, two wires coming off it. When the blower motor is spinning, there should be continuity across the switch. the switch is a differential pressure switch. when the blower is spinning, it iduces an air flow into the switch enough to overcome atmospheric pressure which pushes a rubber diaphragm inside and closes a microswitch. as long as there is air flowing onto the disk the switch is closed. loss of air opens the switch. look on your unit's ladder diagram. it'll show you where it's included in the path to themain valve.

[l8krfan]

Ok, so the air switch is working properly. No continuity when blower is off and continuity when blower is on. So according to the troubleshooting guide on my furnace door the only thing left is the IIBC (circuit board). I tested the voltage at the igniter again and never gets above 7 volts when power is on, blowers are running, and thermostat is on and calling for heat. I also tested the leads for the igniter wires coming off the circuit board and get the same reading (no more than 7 volts).

So I have ordered a new circuit board and will be picking it up in an hour or so. Anything special I need to know about replacing the circuit board? It looks pretty straight forward.

Thanks again for your help.

[HayZee518]

not really. its pretty much straight forward. unlike a computer motherboard where you must be grounded, you don't really need to. make sure the power feeding it is off however.

[l8krfan]

got it installed and furnace is working like a dream. Thanks again for your help. Much appreciated!!

[HayZee518]

glad to hear!