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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Thermostat not activating heat, AC or fan

Customer Question

Thermostat not activating heat, AC or fan
Submitted: 2 years ago.
Category: HVAC
Expert:  Thehvacguy replied 2 years ago.
Hi i'm Gary, first thing you need to do is to go to the breaker box and make sure nothing has tripped, esp the furnace breaker. next make sure the furnace doors are on and secure, because if they are not the furnace power is lost, as a door switch is held in by the doors to give it power. Check these thing's and reply back with your findings/result's
Customer: replied 2 years ago.
Still nothing. It's like the thermostat is not hooked up. The power is on but I cannot here any type of click or anything that it's receiving a command.
Customer: replied 2 years ago.
The AC is the main thing I am concerned with. Cannot even get the fan to come on.
Expert:  Thehvacguy replied 2 years ago.
OK the thermostat may have been ruined from the batteries. to check remove the thermostat from the sub base on the wall. To do this you will see a seam in the thermostat on the side, that go's all the way around it. Use your fingernails on this seam and pull it. This will separate it and expose the thermostat wires on the sub base. Once that is done use a small wire or paperclip and touch the r terminal(red) to the g (green) and tell me if the furnace main house blower come's on. Make sure you do not touch anything else to short it out. You can also remove the red and green wire (Having the breaker to furnace off, or light switch on furnace off.) twist them together and repower furnace and tell me if the main blower come's on.You probably have a bad thermostat from the batteries issue, I just want to prove it before i tell you to buy a new one. This will tell us
Customer: replied 2 years ago.
Tied the green and red together plugged back in and nothing came on.
Expert:  Thehvacguy replied 2 years ago.
Then you have no power to the furnace, or a break in the thermostat line from the thermostat to furnace. again check breakers and kill switch on side of furnace plus the doors are secure and in place. If all is good, remove the furnace blower door, to find the control board. There will be a small mini car fuse usually a 3amp or 5amp. pull it and see if it is blow by looking thru the clear plastic is the wire broken or does it look burnt?
Customer: replied 2 years ago.
Still trying to get panel off. Looks like it should just lift but it's stuck.
Expert:  Thehvacguy replied 2 years ago.
if you mean the furnace it either has screws in the doors and they can come off separate, or if they are lift off the top door has to be lifted off first and then the bottom door. What brand is the furnace?
Customer: replied 2 years ago.
There were 3 wires that were broke off between the circuit board and thermostat. I put them back in using the same color code. Is that correct before I turn the power back on?
Expert:  Thehvacguy replied 2 years ago.
what colors and what terminals did you hook them to? meaning letters on the boards terminal strips

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