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Beaumont 10-20-2010 08:00 AM

Bryant 355MAV furnace
I have a 355 MAV high efficiency furnace. It was installed in 1995. When I run the diagnostic test the furnace goes through the test with no errors, including the blower fan going into low and high spped mod. For some reason when the furnace calls for heat everthing looks and sounds good except the furnace stays in low blower spped and does not go into the high speed mode. I get no error codes. I replaced the circuit board and still the same issue. Any help would be great. Is it time to change the furnace?

gregzoll 10-20-2010 08:05 AM

If it checks out in the self test, next question is, what type of thermostat do you have. Before you started to mess with it, what other things have you done to it prior before posting here?

Beaumont 10-20-2010 08:21 AM

It's a Honeywell RTH8500D touch screen. The only thing I did is change the circuit board in the furnace because I was told that was the problem, but after changing it I still have the same problem.

gregzoll 10-20-2010 08:27 AM

The only other question is, is the thermostat properly set up for your furnace. If it is not, the furnace may not ramp properly. Also, there is a time frame before it may ramp under demand.

Beaumont 10-20-2010 08:50 AM

I will check the thermostat to make sure. I did let it run for 1 hour.

gregzoll 10-20-2010 09:26 AM

If you can not find the manual, honeywell's website has it. Going through the settings on ours, I reloads that it was not set up properly for our furnace, even though I do not remember setting it for a lower efficient type furnace.

There is a setting for single and two stage on these thermostats, in which the furnace needs to have the dipswitches set properly for the furnace to work correctly also.

Beaumont 10-22-2010 06:51 AM

I checked the termostat and everything is ok. Soemthing is not signaling the blower to go inti high speed whn I have high heat.

gregzoll 10-22-2010 07:25 AM

As mentioned before, two things would cause that; thermostat & circuit board settings. Unless something was changed from the last season, which leads me to believe that it was, due to mention of running it in test mode, it should still run like it did last season.

Beaumont 10-22-2010 07:27 AM

I had the same problem last season but did not realize it. The reason I noticed it this year is because when I put on my air conditionner in Luly my system frozeup and that is when I realized my furnace blower would not go into high speed.

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