Propane furnace blows cold air

Old 11-19-12, 01:27 PM
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Angry Propane furnace blows cold air

First let me give you some history. We have an American Standard 90 two stage propane furnace that is just 4 yrs old. We have been fighting this issue for two years and it has gotten worse this year. We have had the dealer we bought the furnace from out to address the issue multiple times and still nothing resolved. The dealer has
  1. Replaced the mother board
  2. Checked fuel pressure
  3. Cleaned thermo coupler
  4. We changed filter monthly (give or take a week or two)
  5. Checked the intake plumbing for blockage
  6. Checked the exhaust plumbing for blockage
  7. changed intake pipe to a 90 on top of furnace and disconnected the external plumbing
  8. Changed the heat exchanger
  9. tried three different thermostats
  10. verified wiring from furnace to thermostat was good
  11. Verified amperage to furnace from breaker panel was correct
Here is what is going on….and it is not ALL the time.
The furnace will blow cold air. We notice this about everyday and when it starts we notice that the thermostat is about 1 degree below the set temp. The error code on the furnace is 21 green flashes and 1 red flash repeating. We have also gotten error 2 green 1 red/green and red then green.
We have reset and saw the furnace start up. It will call for the flame then fire up then run 2 – 10 seconds then flame out .Its almost like it thinks it has a live flame and initiates the blower and then blows cold air until we shut unit down or blower times out (assume it times out when were not home) . we have had it blow cold for over 20 minutes.
Our furnace guy has been great but he like us is frustrated because we can not get it fixed. I am told it is still under warranty but that’s only for parts and a different furnace is out of the question. I am at my wits end as to what to do here. The next closest dealer is over 40 miles away so I really have no other warranty options to use. If anyone has any ideas I may present to the dealer please let us know.

The thermostat fan is set on auto and heat only. It is wired with red – white - green
Old 11-19-12, 02:00 PM
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Would you like me to make a long list of what I think it is ? lol

I know it's not funny, but you can replace the furnace with another one and it will do the same thing if the propane regulator binds? Something like this can wreak havoc on any customer and service tech.

Wow, I don't know if I would have replaced the heat exchanger, that's a lot of work.

Has the tech been on the job when the furnace locked out or started blowing cold?

One good place to start is to have pressure gauges on both the inlet and outlet side of the gas control, and behind the regulator at the house. Sometimes it takes more than one tech to do these tests and monitor gauges.

It just started doing this 2 years ago so I assume the first 2 years were good.
Old 11-19-12, 02:53 PM
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Take off the blower door. On the inside of the door you should find a list of diagnostic codes. Report back with the code and the explanation for the code for each code combination that is being displayed.

Also, take off the burner compartment door and make a note of the furnace model number given on the rating plate. Report that here as well.

While I might respect the enormous amount of work your contractor has done on the furnace, amount of effort is not the same thing as a display of diagnostic skill. Sounds like a lot of guessing and supposing rather than a well thought out diagnostic plan.

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