Ok, I need some knoweledgable help.
I have a 18yo carrier gas furnace (58GP125, split system). Over the summer a mouse fried the control board, which I replaced. Seemed to operate normally for a few months.
When I recently went to heat mode, the fan was constantly running, but furnace wouldn't fire. So I replaced the transformer which also showed signs of having been scorched.
After replacing transformer, burners fired right up. But, I then noticed that in Heat/Auto mode, when heat is called by Tstat, burners fire for about 2 minutes, then cut out and blower kicks on for about 2 minutes, blower cuts out and burners fire. Cycle continues until temp is reached. Presumably, the high limit switch is cutting gas until cooled.
Blower runs fine in On mode, burners fire.
So, now I have pulled the spec sheet for the ICM271 blower control board.
(At the following link http://www.patriot-supply.com/files/icm_icm271-ag.pdf)
Please see page 3 of link for complete verbage, but basically it indicates that the board has an as shipped configuration and instructions to cut the R17 resistor if change to the Blower Operating Modes is necessary. I am having trouble determining if this is the ultimate problem.
Can anyone confirm that cutting the R17 resistor will give me proper blower operation in both heat and cooling mode?
Unfortunately, I no longer have the old board to verify original status.
Thanks for any knowledgeable information!