Ok, so this goes beyond the scope of a typical inspection. Hoping someone knoweledgable can assist a currently nonactive member with a system troubleshoot.
18yo carrier gas furnace (58GP125, split system). Fried control board was replaced. System operated normally in cool mode.
In heat mode, the fan was constantly running, but furnace wouldn’t fire. So the transformer was replaced.
After replacing transformer, burners fired right up. But, 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 and then sequence continues.
Blower runs fine in On mode, burners fire.
So, according to 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. Is this the problem? Will cutting the R17 resistor result in proper blower operation in both heat and cooling mode?
Unfortunately, the old board is not available to verify original status.
Thanks for any knowledgeable information!