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Category: HVAC
Satisfied Customers: 13396
Experience:  15yrs in the HVAC industry with certificates and degrees.
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Have carrier fc4bnf024 split heat pump/air handler.

Customer Question

Have carrier fc4bnf024 split heat pump/air handler. Everything worked fine last weekend and I set thermostat higher when we left to prevent unit from running while away. This weekend I get zero response from AC when I adjust thermostat. Tried to adjust thermostat but AC will not come on. Have checked breaker, main switch at compressor, and all ok.
Submitted: 3 months ago.
Category: HVAC
Expert:  HVAC Guru replied 3 months ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset. I am HVAC Guru an extremely experienced tech on the site and I try to get to as many customers as I can. I just picked up your question now. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly I am not paid anything until you rate my service good using the STAR RATING LINK at the top of your page, the money is paid to the site not me directly.


Check and change the batteries in the thermostat or

What likely happened is the low voltage fuse in the furnace or airhandler blew. There typically is a SLOT STYLE 3-5AMP FUSE on the board itself inside the furnace/airhandler like this.


If that is burned out all power to the thermostat will be lost. 95% of all units use some sort of SLOT FUSE or inline BUS STYLE FUSE to protect the low voltage circuit. You need to find that and change it out. If you just bump two wires together you could have just popped it without even knowing it. Now if for some reason your unit does not use a fuse often the board will be damaged due to the short. You would need to confirm you have 24 volts to the board inside the furnace/airhandler with a volt meter to make sure though.

Note if you have a condensate pump check the float and make sure the pump is not full of that could cut low voltage power to the unit as well if the pump is not working and full of water.

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