Furnace trouble

[Matt Lewis]

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!

[Charley L. Bottger]

Originally Posted by Matt Lewis

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!

Can not trouble shoot your problem from here but what you are describing has the possibility of being a bad Hi-limit switch which is very common on the age of the furnace you have. Could also be a lack of air flow if your furnace A-coil fins are matted over with lint this also can make the limit switch open.

Just curious where is the old board you replaced.

I can not help with the cutting of the jumper on your new board. Something you might check if you don't already know is if you have a dual speed fan motor most common is a low speed for heat and a higher speed for cooling some older furnaces had only one speed not common but occasionally would see one. You can determine this by observing how many leads are traveling to the motor. Two leads for single speed three leads for dual speed.

[Matt Lewis]

Thanks for the reply. Turns out Gas1 - Gas3 jumper was different on new Board. I appreciate the response!