HVAC Blower Motor ?


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Old 11-21-18, 09:38 PM
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HVAC Blower Motor ?

Replacing the blower motor on my 230v HVAC. Looking inside the connection terminal of the motor, I see a white wire (common), black (high speed used for A/C), blue (medium speed used for Heat), and Red (not used/connected to anything). Am I correct in this?

If so is this because A/C requires a higher volume vs the heat (one wouldn't want a breeze on them).

I ask because from what I've read 230v system usually don't use multispeed fans, yet this motor also has a red wire which I assume is a low speed, however it is not connected to anything.

Additional question, I've measured the resistance between the wires and they all show correct resistance and no short to ground. Yet the tech that came out stated the motor was bad. I didn't check his work until I removed the motor but now I'm thinking of going back up on the roof (package unit) and checking to make sure it was getting voltage.
 
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Old 11-21-18, 09:44 PM
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Yes...... you are correct. That is a multispeed motor and typically the A/C uses the high speed and heat uses the medium or low speed. You didn't say why it was thought to be bad but it could have bad bearings.
 
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Old 11-21-18, 10:06 PM
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It was actually at my parents house so I didn't talk w/him. He wanted $800 to replace it. When I looked at the motor the bearings seemed fine, no resistance. My parents told me the there was no air movement out of the vents so I assumed the blower wasn't spinning that's why I went directly to pulling the motor and assuming it was electrical related (sort of relying on the tech).

(I had a small window between the rain to pull the motor which I why I didn't check anything else).

So if all the resistance measurement seem okay (the different taps add up correctly), The brwn/whte seems direct to the common, no shorts etc, would that indicate the motor is okay?

If so, I'll probably wind up connecting it up tomorrow (without the squirrel cage) just to see if it spins.
 
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Old 11-21-18, 10:14 PM
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Brown/white is a capacitor connection wire.
 
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Old 11-21-18, 10:29 PM
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Affirm, it and the plain brown wire. I've read that the resistance to the common wire (wht) should be close to 0, which it is. The plain brown has a higher resistance.

The high to medium + common to high = Common to medium, which from what I've read is correct.
 
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Old 11-22-18, 06:48 AM
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Hi, what voltage are you getting between the White and Black conductors , can you post a wiring Dia. could be a bad fan relay.
Geo
 
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Old 11-22-18, 01:48 PM
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Hmmm..... connected everything back up and it seems to work. Not sure what the tech was looking at??? I amped the motor and it was within spec. Has been running as it should for a couple of hours.
I don't want to say for sure the tech was a **** but I'm starting to lean that way.

Not sure if anyone knows the answer to this but I am curious. The motor is a 240 volt. So when the fan is called for I get the the correct voltage between the leads. However when the fan is not called for I get around a 60v constant reading. Shouldn't it be zero or is it because it a 240 system it's normal to have that?
 
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Old 11-22-18, 02:09 PM
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Seeing stray voltages with a digital meter are not uncommon. They're also called ghost voltages. The wire you are testing is running next to a live wire and the voltage gets inductively transferred to the dead wire.
 
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Old 11-22-18, 02:15 PM
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Argg....you know I've read that on here so many times but I didn't even think about that. Thanks!
 
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Old 11-24-18, 12:21 AM
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And now nothing turns on. 27v to the circuit board (and coming out the thermostat terminals) but no relays tripping or any response when calls for heat or cool are requested. The full 240 is coming in where it should be. Circuit board shows overheating and one of 4 identical resistor nears the discoloration measures incorrectly. Not sure if that is the cause. The LED diagnostic light blinks like there is a call for heat no matter if I jump the Cool or Heat leads. It just sits there blinking at me....grrrr..

Thus I've ordered a new board as I'm hoping that is what is wrong with it. I hate throwing parts at it, but as everything else seems to test okay, it's all I'm left with.

This is the board

https://www.hvacpartsshop.com/12j99-...control-board/

The overheat is in the upper left where there are 4 resistors. The "bad" resistor is second from left and connected to the R terminal via the circuit board.

Any other ideas out there?

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Last edited by PJmax; 11-24-18 at 09:40 AM. Reason: labeled picture
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Old 11-24-18, 09:43 AM
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I marked where the fuse is and the 24vAC transformer connects TO the board. This is probably ok as you said the red light was flashing.

If you don't see 24vAC on the R and C terminals....... you may have an open limit switch. That would mean the LED should be flashing a fault code.
 
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Old 11-24-18, 10:15 AM
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Fuse is good as is the 24v coming in. I did not measure between R and C. I will when I go to replace board just to be curious. The LED was not flashing any code except the steady "Fast" flash which I read as a Heat call.

Do I understand that a limit switch is usually closed until it heats up enough to open to tell the board to start the blower. And if it open prior to burner operation then the board would send the fault code? If so, then it shouldn't have an affect on the cool side of the operation? Remember, the A/C won't start or do anything also (I've push the contactor in to verify that the compressor does still run). Or might it do this safety check in either mode.
 
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Old 11-24-18, 11:00 AM
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Typically the limit switches or sometimes just one of them is in the R line so that if it's open.... you won't get 24vAC on the R line. The limit switches are normally closed and remain that way until tripped. Most are self resetting. The burners are manually reset.
 
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Old 11-24-18, 11:43 AM
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Okay, so more than likely they are ok since no error code on the LED and did measure 24v via the W and Y wires. The board should get here early next week....
 
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Old 11-24-18, 08:21 PM
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Uh Oh....this is from the service manual. If I read it correctly, the fan should blow high during heat and medium during cool. Backwards from what I thought. Is this common? And other than blowing too fast could it have caused any damage, i.e. damaged the circuit board?

Note: The circuit board was discolored before I started anything so some damage was already there.
 
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Old 11-24-18, 08:33 PM
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Yes..... that is backwards from typical home systems.
Running the speeds opposite does not harm or cause the control board any problems.

Those resistors are part of the 24vAC---->12vDC on board power supply.
They do run hot and get discolored with age.
 
 

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