View Full Version : Carrier upflow furnace

Dec 27, 2006, 02:41 PM
I Have an older ( 6 yrs old) carrier upflow natural gas furnace.
Since purchasing the house it came with I have not been able to maintain a constant temperature. The furnace fan comes on, stops, the small blower fan starts and follows with the igniter and gas ignition. It will run for a few minutes then turn off. Great.
Then it will do nothing till I go and turn off the power and back on again. I thought it might be the thermostat so I installed a new honeywell digital thermostat.
First day pretty good, but after that I have huge heat swings.
One day it will maintain 70 degrees. The next it will be 58 when I get home.:mad:
The thermostat is programmed to run a schedule of a constant 70 degrees.
I am unsure of what this issue is.
Any help would be appreciated.

Dec 30, 2006, 02:17 PM
I would hate to tell you to replace the control board when the problem was a limit switch. Turning the power off and back on again shouldn't have much effect on a limit switch or flame detector.

Dec 31, 2006, 09:43 PM
This sounds very much like a problem I just had with my unit. Mine is also a carrier but downflow.

See my thread below. For a shortcut of all my trouble shooting, if you can have a voltmeter connected at the draft inducer, then wait for the unit to do its cycle. Check the voltage when this happens. It should read 0, then 120V when the inducer starts, then flame ignitor starts then gas valve, flame, main fan...

If this issue is the same, you should hear a click and you should see that the inducer is losing speed, at this moment check if it is getting still 120V... if so just to make sure, turn off the unit totally, and run 120 volts direct to your inducer and see if it stops... if so, you got the cause.