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-   -   Carrier furnace fan won't switch on (http://www.houserepairtalk.com/f8/carrier-furnace-fan-wont-switch-8992/)

Augment 04-07-2010 10:43 AM

Carrier furnace fan won't switch on
 
I have a 10 year old Carrier furnace. When in heat/ac mode the fan will work, but it won't run continuously in "on" mode. When the heat/ac is "off", and the fan is "on", it won't work at all. It used to work continuously when in "on" mode. The blower motor was replaced a few months ago and the problems started then. The LED light is not showing any problems. Is there a quick fix?

kok328 04-07-2010 01:19 PM

Check to see if the green wire or wire from the G terminal on the thermostat is hooked up and likewise at the thermostat terminal connections inside the furnace.

Augment 04-07-2010 02:09 PM

yes, the green wire is hooked up on the thermostat and the furnace.

kok328 04-07-2010 02:45 PM

What happens when you jumper 24V from the red wired to the green wire?
If you remove the furnace panel door, make sure the safety switch doesn't cut power to the unit while testing.

Augment 04-07-2010 02:51 PM

I wouldn't know how to do that - please explain!

kok328 04-07-2010 03:24 PM

Oh sorry, sometimes I assume too much.
Take a piece of wire and strip the two ends.
Touch one end to the "R" terminal and the other end to the "G" terminal on the thermostat terminal strip inside the furnace.
As I mentioned, there may be a safety switch that will kill power to the unit when the access panel is removed. For the most part, you can just hold this in to restore power while testing.
Jumpering the R&G should run the blower motor.

Augment 04-07-2010 07:26 PM

What would I be achieving by doing this? I'm reluctant to try anything without knowing why I'm doing it. The blower motor does work if it's in heat mode, just doesn't stay on continously even tho the fan setting on the thermostat is set to "on".

kok328 04-07-2010 08:43 PM

I'm trying to guide you in troubleshooting the circuitry of the unit. This will basically tell us if the T-stat is bad or if there are other issues preventing the fan from working in the "On" setting. It's only 24VAC so no safety issues to be concerned about. If you prefer an alternate technique, you'll need a voltmeter. Turn your tstat to fan "On" and check for 24VAC from ground to "G" (green). This will tell me if the tstat is energizing the fan circuit or we can just energize it and see if the fan comes on which is what I was attempting in my prior post.

Augment 04-07-2010 08:58 PM

I don't have a voltmeter, but will attempt the test tomorrow. If the fan is energized this way, does it mean the tstat is bad?

kok328 04-08-2010 05:43 AM

If the fan turns on as a result of the test, it will either be a bad Tstat or the wiring from the Tstat to the furnace.
If you'd like, you can jumper the R & G terminals on the back of the Tstat and this will verify the wiring and result in determining a bad Tstat.


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