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The blower motor stopped working on my Lennox AC unit B24Q3.5-1P.

I am electric savy an...
The blower motor stopped working on my Lennox AC unit B24Q3.5-1P. I am electric savy an prefer to do this myself. Trying to get some tips on specifics to look at before I start digging. I have pictures of wiring diagrams off the blower itself.
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Answered in 1 minute by:
6/19/2010
Richard
Richard, Technical Manager
Category: HVAC
Satisfied Customers: 1,514
Experience: 27 years of Experience, NATE Certified, professional trainer
Verified
Chat Conversation Started
Richard :

Hello

Customer:

hello

Richard :

I am assuming your talking about the outdoor condensor fan motor? If so, this is pressty straight forward. however before you replace the motor you might want to check the capacitor. Do you know how to do this?

Richard :

Hello

Customer:

The motor I am taling about is the one that forces the air though the ducting. Is that the condensor fan motor?

Richard :

Alright this will be a little different

Richard :

Do you have a volt meter you can use?

Customer:

Yes

Richard :

Alright will the fan run if you set the thermostat to fan ON?

Customer:

No, I have alternated between auto and on, with no change. fan does not kick on at all.

Richard :

There must be a little problem with the site I had sent you another message. however, locate the blower section ( gas furnace?) find the fan motor there will be several wires coming from it. the white is the nuetral and the otheres a various speeds. Typically black the cool but not always. the board may be marked. Set it to cool and check for power. This typically a PSC motro so there might be a capacitor on there as well. Do you know how to check that? Next if no power make a jumper wire from R to G on the low voltage thermostat connections and tell me if the motor comes on then

Customer:

I know how to check the cap. This will take a moment.

Richard :

ok

Customer:

The capacitor is bad. I will recap, so you can let me know if there is something that I may have misstepped. I securred power to the unit.

Customer:

Then shorted the leads on the capacitor. should have brought its potential to 0.0 I set my multimeter to 2M ohms and checked it and it stayed at 0 ohms.

Customer:

I am going to check one more time, because I did not disconnect it from the rest of the gear.

Customer:

The capacitor is working fine. I isolated it and grows to infinite the way it should.

Customer:

I reconnected the capacitor, applied power, set the unit to kick on. I felt the coils start to cool and put a jumper between R and G, but nothing happened.

Richard :

hello

Customer:

I am on

Richard :

Check for voltage between cool and neutral on the board you should have power if not check for power between Y and C on the low voltage wires and G and C

Richard :

if you try to spin the motor by hand will it spin freely?

Richard :

you can try another speed but if you have power the motor has probably failed

Customer:

I had 0 at cool and neutral. 0 at Y and C. 26.6 v at G and C. I will go check motor freeplay.

Customer:

The motor spins easily

Richard :

Hello

Customer:

hello

Richard :

This might be your problem if you had no voltage between Y and C either the thermostat failed or was not set to cool and temp lowered or a broken wire. R is the 24 volts to the stat on a call for cool it energizes the Y terminal

Richard :

put a jumper from R to Y on the board nd tell me what happens.

Richard :

Thank you

Customer:

So when I set the AC on, and the fan should be blowing, I should see 0 volts at Y and R.

Customer:

I set the power on, motor should have been on. I had 0 at y and r. 26 at y and c. 26 at y and neutral, and 26 at g and c.

Richard :

Yes 0 at Y and R and 24 at Y and C

Richard :

If no power at the motor your board may have failed or a loose wire. Can you put power direct to motor?

Customer:

I am not sure how to do that.

Customer:

JUmper?

Richard :

See if you can take the motor leads and hook them to direct power. if there are open terminals on L1 and Neutral or and extention cord. Only do this if you feel comfortable. i just want to make sure the motor will run beofre I tell you , you have a bad board.

Richard :

If you had power to Y and C there should have been power at Cool and neutral

Customer:

Now I am not sure if I had neutral right or not. My diagram is showing Y1 (yellow) is cool. R (red) is power. G (green) is blower. w1 (white) is heat, C (blue) is common. I have been checking as if w1 is neutral. Nothing is labled neutral so I went with white as neutral, but now I believe that is wrong.

Customer:

Is C (blue) also my neutral?

Customer:

I have access to the leads to the motor. So potentially if I have the motor power applied at the board leads and the motor is not on it should be the motor. If there is no power at the leads to bring the motor on when there should be, then it is the board?

Customer:

With AC on and fan set to on, I checked at the fan motor. At the motor, Blue (Low), then Red(med), and then Black (high) to Ground and all showed 120VAC. I would think that there should be something there to limit which one the power is coming from (low, medium, or high). Diagram shows the other orange lead, but that is taking back to the transformer.

Customer:

I have some good pictures of the board and the diagram, but I don't know how to post it, in this chat room. Is there an email I can send the picture to.

Richard :

Hello

Richard :

You can not send email through here. However you have 120 volts from all of the motor speeds to neutral at the same time?

Customer:

Yes

Richard :

To be sure you were not measuring feedback take the motor leads off the board and measure voltage at the board.

Customer:

I will try that

Richard :

Ok let me know what you find.

Customer:

I pulled the motor connections off the board, turned ac and fan to on and got nothing at the board. Then just to double check witht the connections removed, I got 120V at the motor again, so it was feedback of the transformer.

Richard :

Hello

Richard :

i am not exaclty sure why you have voltage there but the low voltage transformer should not influence the readings on the motor terminals. With the leads off are you able to hook up power to the motor to see if it will run. it is sounding like a failed board but i just want to be sure.

Customer:

I tried to figure out the way to check the blower motor, but with the confined spacing and lack of experience, I am not that comfortable with it.

Richard :

Use your ohm meter to check the motor. One side to the White then check to the remaining leads.

Customer:

From the looks of the board, I did see a resistor that looked burnt. It did not show infinite, but it did show a lot of resistance. About 1.4 megohms, if I remember correctly, that is pretty close to being an open.

Richard
Richard, Technical Manager
Category: HVAC
Satisfied Customers: 1,514
Experience: 27 years of Experience, NATE Certified, professional trainer
Verified
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Richard, Technical Manager
Category: HVAC
Satisfied Customers: 1,514
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