Rheem Gas Furnace RGDG-07NAMGR suddenly not working

[lotsaspots]

Rheem natural gas forced air furnace installed in 1982.  It has worked fine the past 7 yrs I've lived here, until yesterday.  Normally, when I turn up thermostat, I hear low drone for ~ 30sec + 4 or 5 chirps (~ 10sec apart), and then blower comes on & heat comes out.  Now, I turn up thermostat, I hear a low weird hum, no chirps, blower does not come on.  Any ideas?  (I've disconnected ignitor in the pic just to look at it).  Thanks,... Diane.

[hvacdrd]

Sequence of operation is as follows on a call for heat.

1 - Exhaust motor starts (located top center in your picture)

2 - Pressure switch contacts close (pressure switch located left side, orange tubing connected between it and the Exhaust motor)

3 - Ignitor (located in front of right burner) warms up approx 30 seconds (it will glow orange) unless you have spark ignition(picture isn't clear enough to tell)

4 - Gas valve opens, 5-7 seconds to prove ignition

5 - House blower starts approx 60 seconds later

where are you at in this sequence?

[lotsaspots]

I was actually at the beginning of the sequence-- exhaust motor did not start, nor anything else.  Funny thing...  it's working fine now.  Earlier I had disconnected main power & gas, but no change.  This time, I turned off the on/off dial on the Honeywell "Hot Surface Ignition Valve", then turned everything back on, and all is well.  I'm baffled.  I'm quite the Miss Fix-it but mechanics & electronics are not my thing!  I've attached a "Sequence of Operation" from the manual.  From what I'm reading, is it likely that the ignition portion is beginning to fail (i.e., the flame didn't light and so the system locked down)?  Or is there another problem?

UPDATE: Not working again!!!!!  Help!

[lotsaspots]

O.K. so this is what is happening.  The heat system only hums and nothing comes on, UNTIL I turn the exhaust motor manually (with a thin stick I put through the cover!).  Then the exhaust motor starts, the ignitor thingy lights up, the gas burners ignite, and the house blower comes on, and all is well!  For now.  So does this mean the exhaust motor is going bad, and if so, what is a reasonable cost to replace it?  Is it something I could probably do myself?  Thanks again,... Diane

[hvacdrd]

You are good if you managed to get the motor up & running. :clapping: Can you get me the numbers from the motor so I can cross reference the part? Or even a close up picture of the motor info plate. It is a straight forward job and since you made it this far I'd like to see you take it all the way.

 

Are one of the numbers 70-22838-02 , 70-24157-03 , 055660 or 66838 ? If so it is one of the more expensive draft inducers. Retail is around $300

[Pegi]

If this is  capacitor run motor it could just be a bad capacitor also....

[hvacdrd]

That would be nice but it is built similar to an evap motor on a refrigerator. Note the winding block at the 10-11:00 position in the first picture. I'm not sure why the manufacturers have gone to this style motor on the draft inducers, they don't hold up nearly as well.

The high price is because they only sell them as a complete assembly, you cannot get just the motor.

[lotsaspots]

On the metal casing around the motor fan, Ametek model # is 117104-01.  Note: I can't find the part online with that Ametek model # BUT check out this forum & Irascible's post advice on the part replacement: http://hvac-talk.com/vbb/showthread.php?threadid=77432.  Also, this site says the current replacement does not allow for a "Sensor Mount": http://hvac-talk.com/vbb/showthread.php?p=1704090.

[hvacdrd]

The Ametek number 117104-01 crosses to the Rheem part number mentioned above 70-24157-03. This also crosses to part# 055660 but I am unsure of who makes it

[lotsaspots]

Do you think I would have an issue with the part not being a good match?  I'm particularly concerned about the sensor not having a connection on the replacement part.  What would I do if that is the case?

[hvacdrd]

The article you linked was not very clear what this "sensor" was. From your picture I do not see anything other than the wiring to the motor and a connection for the pressure switch. Standard stuff on any inducer.

The two red wires on the left of the motor look like they go to a limit above/left of the housing. If this is correct I don't see an issue.

Here is a link to a site I found doing a part search, this picture should give you an idea of what you will be getting as a replacement.

[DwightCSr]

DO WE REALY NEED THAT LITTLE FAN AND IF WE DISCONNECT IT ARE THERE ANY ISSUES

[DwightCSr]

I AM HAVING THE SAMER ISSUES. WHAT IS THE RESOLVE?

[ACtechGUY]

The furnace will not heat without the inducer fan running. Have the inducer assembly replaced if you are sure that this the problem.