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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8389
Experience:  Furnace, A/C and heat pump specialist.
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I have a Carrier heat pump model number FB4ANF024. I have a

Customer Question

I have a Carrier heat pump model number FB4ANF024. I have a Nest thermostat attached to the unit. The Nest thermostat indicated that it was not receiving power from the furnace. I opened the furnace and noticed that the LED on the control board was not lit. The fuse on the control board is not blown. Could it be that the control board has gone bad?
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

More times than not, there is a break in the low voltage circuit.Do you have a drain float switch or anything in the circuit.Otherwise start by checking 24 v out of transformer to board.

Customer: replied 1 year ago.
There is not a drain float switch. I'll have to borrow (or buy) a multi-meter to check the transformer.I've attached a picture of the board. There was some discoloration on the R1 and R30 resistors which made me suspect the board. I'm not sure if that is normal or not so I'd though I'd include a picture.
Expert:  airheatman replied 1 year ago.

Thanks for the pic. The discoloration is not normal as it indicates they have been warmer than normal. Lets get that meter and check our voltage though before condemning.