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Old 08-28-2013, 01:08 AM   #1
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Carrier - Blower fan NOT coming on


Hi,

Other day I noticed AC was not blowing cool air anymore. I check on the breaker and everything was in place. Thermostat was calling for cool. I also jumped R and G, still blower fan will not come on.

I did component self test by briefly shorting TEST to COM terminal, everything came on except blower motor. Following that I turned off thermostat and disconnected BLACK/YELLOW/BLUE/RED wires of blower fan from control board. I hot wired BLACK wire to incoming 115V AC, still blower fan would not come ON. It just sits and makes hummmm sound.

Blower fan is not locked up, I can move it freely in squirrel cage. I did resistance measurement between blower terminals (all disconnected from board).

White & Black --> 2.5ohm
White & Blue --> 3.5 ohms
White & Yellow --> 4.1 ohms
White & Red --> 4.9 ohms

Brown and brown --> 36.6 ohms

Tomorrow I will check on the capacitor value. I need to get a multimeter which can measure capacitor.

Based on above info, do you think I need to replace blower motor ? Can we determine state of blower motor from resistance value ? Or resistance is of not much use ? Again just makes humming sound and does not come on. If you leave it power like that for some time, motor casing is getting hot too.

Appreciate any insight here. Thanks for your help !

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Old 08-28-2013, 09:59 AM   #2
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Carrier - Blower fan NOT coming on


Yes, the resistance test is of great value. It appears you had the right idea but tested the leads in an incorrect manner. You will need to identify which of the leads is common, which is start, which is run, which is low speed, medium speed and high speed. You also need to check each of the fan motor leads to see if the windings are shorted to ground. Turn off all power to unit. Set your meter to ohms and place one of the meter probes to the terminal of one of the motor leads. Touch the other meter probe to ground. The metal cabinet of the furnace or air handler will work. There should be no continuity between any of the leads and ground. The meter should read OL (infinity) for all leads to ground. If you have a digital multimeter that emits a tone when there is continuity it makes it easier to test. If the meter beeps when doing the test then you know one of the windings is grounded and the motor is bad and needs to be replaced. Here is a link to a video that explains the procedure better than I can write it: Do the test and then come back and let us know your results.

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Old 08-28-2013, 10:07 AM   #3
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Carrier - Blower fan NOT coming on


All you need to do is check the capacitor. If it's good and the motor doesn't come on with voltage applied then the motor needs replaced.
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Old 08-28-2013, 10:42 AM   #4
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Carrier - Blower fan NOT coming on


If the capacitor checks good, see if the motor shaft will move up and down. Sometimes the front bearing will go bad and the motor won't start because internally the spacing is all wrong due to a bad bearing.

If the capacitor is bad, replacing it should solve the problem.
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Old 08-28-2013, 02:33 PM   #5
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Carrier - Blower fan NOT coming on


Quote:
Originally Posted by anku View Post

Based on above info, do you think I need to replace blower motor ? Can we determine state of blower motor from resistance value ? Or resistance is of not much use ? Appreciate any insight here.
I agree the problem is more than likely the capacitor. I was providing answers to the questions OP asked. He stated he was going to test the capacitor. Since the motor gets hot that shows there is power to it.

Since the fan relay board was bypassed and it still didn't start that would leave the capacitor or fan motor. The capacitor is relatively cheap and easy to replace. If the capacitor tests good the fan motor needs to be replaced. I always like to verify when a fan motor is bad... But that is just me.

Last edited by firedawgsatx; 08-28-2013 at 03:25 PM.
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Old 08-28-2013, 08:39 PM   #6
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Carrier - Blower fan NOT coming on


Thanks everyone for the reply.

I got a digital multimeter which could measure capacitor. It's reading 0.95nF, when capacitor is supposed to be at 10uF. Now I am off to finding capacitor locally (instead from internet to get it faster) and see if that solves the problem. As everyone has suspected .... I am hoping it will. I will update once I have new capacitor.

Here is more info on wire and resistance.

White(common) & Black(HI fan speed i.e. run/cooling) --> 2.5ohm
White(common) & Blue(MED HI/LOW speed/heating) --> 3.5 ohms
White(common) & Yellow(MED HI/LOW spare1) --> 4.1 ohms
White(common) & Red(LOW spare2) --> 4.9 ohms

Brown and brown(run capacitor wires) --> 36.6 ohms
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Old 08-28-2013, 10:36 PM   #7
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Carrier - Blower fan NOT coming on


Yes, it sounds like it is the run capacitor. As far as checking the resistance on your fan motor. You need to check the resistance from white (common) to the solid brown wire and from the black wire to the solid brown wire.

A. White(common) & Black(HI fan speed i.e. run/cooling) --> 2.5ohm
B. White(common) & Solid Brown --> ????
C. Solid Brown (run) & Black(HI fan speed i.e. run/cooling) --> ???


A. + B. readings should should equal the C. reading

Example: readings of A. 20.5 ohms B. 20 ohms C. 40.5 ohms

20.5 + 20=40.5 ohms.

You would still need to do a short to ground test
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Old 08-29-2013, 10:49 PM   #8
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Carrier - Blower fan NOT coming on


Resistance measure was between different wires to common made sense. There was no short from any wire to ground (Note : make sure you disconnect all wires including WHITE/common for ground test).

I found replacement capacitor(DAYTON Run Capacitor, 10 MFD, 440 VAC, Oval) at local Grainger store. Replace faulty run capacitor with new one and violla !!! ... blower motor came to life

Thanks everyone !!

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Old 08-30-2013, 08:46 AM   #9
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Carrier - Blower fan NOT coming on


Glad to hear you are back up and running. Thanks for letting us know. It is nice to hear the outcome because it helps others who might be in the same situation.

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