Only main blower

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  #1  
Old 01-24-04, 11:31 PM
rurlprsn
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Only main blower

I have a Carrier unit on the roof top. A/C & Heat. The Heater and A/C have been working fine. About 3 days ago the heater was on and blowing hot air, but after a while we noticed NO heat was coming out of the vents, just cool air.

I tested the thermostat (electronic) in all positions Heat & Cool with negitive rusults. Then I went up on the roof and opened the cover on the heating side of the unit to check. Nothing was working, not even the inducer motor.

The only way I can turn off the blower is from the main electrical panel.

I checked the induction fan blower to be sure it was not frozen or stuck, blades not in contact with the blade cage, etc.

I checked the vacuum lines to and from the inducer fan. There were no restrictions.

I checked the T-Stat. It has no power.

I tested for 120 AC volts in and 24 to 28 volts DC out. The transformer is not burned out, and is working properly.

I did determine that the power vent fan motor was not recieving voltage from one of the circuit board leads. I jumped from a known source of current and the motor started running.

What do I have to do to get my unit running again?

Lee Latting
 
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Old 01-25-04, 06:07 AM
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On some unit, when you remove the cover, the syste will not work. Look for a safty swich first..

Take your meter and read R and W on the control (t-stat wires hook up to) You should read around 24 volts. if no reading there, try R to C or ground. and if O, then you are not getting power. Check the backside make sure something dind't get burn off.

If you are reading 24volts at R and W, then you get O at the T-stat in the house on the wires. then you have a bad wire between the unit and the t-stat.
 
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Old 01-25-04, 06:10 AM
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Well, what you know is that you have line and low voltages and the inducer motor is good.

What you will need to find out is what comes in the circuit before the inducer motor. I don't think there is much. If a high limit tripped, you would think they would want the inducer to stay on too, but maybe not. If a spill switch tripped you definitely would want the inducer running. If the flame went out or failed to light, I suppose the inducer would stay on also. I know I'm not helping you a whole lot, but I'm trying to work through the possibilities as you will ultimately have to find the problem or call someone who will. If the blower is running and you have the thermostat calling for heat, it sounds like the furnace is wawre of the call for heat. Have you reset the power to recycle the safety control? It is possible that the flame failed and after 30 minutes the inducer shuts off too. If you access the area that has the circuit board, which I think you already have, see if there is an LED to flash a fault code. That could be helpful. Otherwise, post back after you have recycled power and let us know what the result was.
 
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