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M Oglesby
M Oglesby, HVAC Technician
Category: HVAC
Satisfied Customers: 2038
Experience:  Universally Certified HVACR Technician
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carrier gas heater will not run in auto; burner comes on but

Customer Question

carrier gas heater will not run in auto; burner comes on but fan never starts. Heater will work in manual fan mode. in air conditioner mode auto works fine. what gives here?
Submitted: 3 years ago.
Category: HVAC
Expert:  Douglas replied 3 years ago.
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

The furnace uses the same fan motor for both heat and cool, however it uses different speeds and therefore two different relays to turn the fan on. In cooling and on manual fan, it uses the relay marked cool on the control board. In heat, it uses the relay marked heat as you would have guessed.

These relays are intgrated into the control board. In all likelyhood the control board in the furnace will need to be replaced. The relays, unless a real old furnace are not removable. The only other option is if that heat speed on the blower motor itself is burnt. This latter cause is very rare.
Customer: replied 3 years ago.
this is a very old furnace! only model number I could find was(NNN) NNN-NNNN no the alphanumeric model numbers I searched for instructions on the carrier website. there is actually electromechanical switches in the control box
Expert:  Douglas replied 3 years ago.
Ok, then one relay is marked heat. I also dont recognize the furnace and cant look up a diagram, but if you can look at the relays, one may be marked heat, the other cool. If there is only one relay, its the heat relay and the cool relay is served through the "fan center".

Can you take a picture of the controls and post it here?
Customer: replied 3 years ago.
yes i will take photo, one minuite
Expert:  Douglas replied 3 years ago.
Ok..great
Customer: replied 3 years ago.
photo1
Customer: replied 3 years ago.
circuit board
Customer: replied 3 years ago.
do you need more photos?
Customer: replied 3 years ago.
hello???
Customer: replied 3 years ago.
Relist: Other.
never heard back waited 40 minutes
Expert:  M Oglesby replied 3 years ago.
There is a red and black wire coming from the fan motor to the control board, switch these two wires and attempt to call for heat. Tell me if the fan comes on then or not.
Customer: replied 3 years ago.
I posted two photos and you can see there are not a red and black wires from my fan motor, there are multiple wires coming off the fan motor (some not connected - related to fan speeds?). tell me where on the control board to swap the two wires you are trying to change.
Expert:  M Oglesby replied 3 years ago.
How many wires are coming from the fan motor and what are their colors?
Customer: replied 3 years ago.
see photo in the post above Friday, December 17, 2010 11:37 AM
Expert:  M Oglesby replied 3 years ago.
I don't get a good view of the wires coming from the fan motor. I will need your help identifying. The bottom view of the photo is cut out.
Customer: replied 3 years ago.
from the motor, i can see white connected to white on left; red connected to black on left; black and blue wires from the motor are not connected to anything
Expert:  M Oglesby replied 3 years ago.
I don't understand what you mean when you say red connected to black on left. Please Elaborate.
Customer: replied 3 years ago.
referencing the photo's "left" side. so the red wire from the motor on the right side of the photo is connected to the black wire on the left side of the same photo. the technician used twist nut to connect them, which is out of view on the bottom of the photo
Expert:  M Oglesby replied 3 years ago.
ON the board, the red wire that is next to the black wire, where does it come from?
Customer: replied 3 years ago.
ON the board, the red wire that is next to the black wire; that red wire is not connected to anything. REd wire ends in a box shaped connecter
Expert:  M Oglesby replied 3 years ago.
Try to connect the the black wire where the red wire is coming from the fan motor. Change them out. These represent speeds from the fan motor. Then try to call for heat once you are done. Make sure power is off before attempting this. When finish turn power back on and see if the fan comes on.
Customer: replied 3 years ago.
to be clear, you want me to disconnect the red wire coming from the motor connected to the black wire that is connected to the circuit board above post EAC-1. then connect the black wire from the motor to the black wire above EAC-1. correct?
Expert:  M Oglesby replied 3 years ago.
Yes.
Customer: replied 3 years ago.
swapped the wires but same problem; started heater in auto, burners came on but fan never did.
Expert:  M Oglesby replied 3 years ago.
That means you have a bad control board. The Heat RElay is not causing the contacts in the Blower relay to close. This all takes place on the control board. It will have to be replaced. Please hit ACCEPT so I can be paid for my time. Bonuses and positive feedback are greatly appreciated especially since I only get half of the $15 that you are paying. Thanks, XXXXX!!
M Oglesby, HVAC Technician
Category: HVAC
Satisfied Customers: 2038
Experience: Universally Certified HVACR Technician
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