Air Handler Motor Wiring

brando1118 · 06-01-2010, 09:43 PM

Hello,
I've got a VERY old Rheem air handler and the blower motor just quit on me a few days ago. I've replaced the capacitor which is a 10/370 and still no joy. Neither motor makes a hum, a buzz or tries to turn at all. I will explain how the old motor was wired which is a two speed and then I will explain how I wired the new one which is a three speed. I've also taken some photos to help explain.
Below are the three hot wires coming from the air handler.
1 Red (only reads 120v when hooked up to the motor and power is on)
1 Black (only reads 120v when hooked up to the motor and power is on)
1 Orange (which is a constant 120v with power on)

This is the relay:The top right black wire and the bottom middle red wire (burnt) are the black and red wires you see in the photo directly above.

The old motor has 6 wires and all were used:
1 Red
1 White
1 Black
1 Brown attached to the capacitor
1 Brown w/white stripe attached to the capacitor
1 Green small wire for ground
It's a 208-230 1ph motor. When I have the breakers on and try to power the motor on I hear an audible "click" from the relay and the capacitor becomes charged. Please note that the burnt connector on the capacitor was me accidentally arcing the connector on some metal. The capacitor tests fine and holds a charge. This is how the first motor was wired up:

The new motor has 7 wires (not counting the reverse direction wires which there are 4 of them.
1 Red
1 White
1 Black
1 Blue (capped)
1 Brown attached to the capacitor
1 Brown w/white stripe attached to the capacitor
1 Green small wire for ground
It's a 208-230 1ph motor. Again with the power on I turn on the fan and hear the relay "click", but the capacitor does NOT become charged. This is the clue that I'm doing something wrong, but what? Here is how I wired the new motor. Note: the blue wire is not connected:

Now when I'm testing these scenarios, all wires are capped. Is there a way to bench test these motors? The old motor failed an ohms test between the white to black, black to solid brown and white to solid brown. The ohms didn't add up. No where near. The new motor tested exactly the same way had the ohms add up perfectly.

Here is the diagram on the new motor:

Any help is appreciated.
Thanks!!
-B

mikethe ductman · 06-01-2010, 10:52 PM

Here we go again.
I don't know if this will help, but I come across a brynt a couple months back with no funny papers so I had to track down all the wires
It had 2 contactors that controlled the fan
Contactor 1 n/c contacts went to cont. 2 n/o contacts" when green was energized it closed contactor #2 n/o contacts to bring on the fan on high speed "black wire"for cooling or fan on mode"
Thats how high speed worked.
Now for med or low speed for heat
Med or low speed worked off contactor #1 n/o contacts
When there was a call for heat, the heat strips would come on, they would heat up a disc that would close on temp rise.
When the disc closed it sent 24 volts to contactor #1 closing the n/o contacts and making sure that high speed never came on at the same time as med or low speed.
One thing to try is only hooking up the black or red and see if it runs, you might be trying to run the on two speeds at the same time.

yuri · 06-01-2010, 10:55 PM

Check for 240 volts ACROSS the 2 hot supply wires to the airhandler. If one leg is dead/blown fuse/breaker you can get 120 to ground on the wires you tested. Common mistake when checking A/C units. You need to have 240 to the white and whichever motor speed is being used also. 120 to ground is not a foolproof way to check. Poor and corroded connections can also be a problem. Even reading 240 volts can be deceiving if the connection is so poor it won't allow enough current to flow. Check the connections at the breaker and buss bars in the electrical panel. I have had breakers and disconnect switches look good but corroded internally and fall apart and drop voltage/not allow current flow properly.

Houston204 · 06-01-2010, 10:57 PM

Probably a bad fan relay.

Remove power.

Move the wire on terminal 3 to terminal 2.

Remove and tape off the wire on terminal 5 (to avoid possibly energizing 2 speeds simultaneously)

Restore power.

Fan running?

brando1118 · 06-02-2010, 07:53 AM

Hey guys, thanks so much for the replies.
Mike: All I can say is I hope that is not my setup.
Houston: I didn't have time to try the configuration you suggested. I had to get to work. Will do when I get home.
Yuri: I took some more photos to show you my setup. I am definitely NOT getting 240v on ANY of my three wires(red, black or orange)

Orange: 120v constant
Red: 120v only when wired to the motor's red wire.
Black: 120v only when wired to the motor's black wire.

In the photos below, you can see the low gauge, black wires coming out of the breakers and where they are screwed into the buses at the top of the box. I took a closeup of the orange wire (the same orange wire that I hook to the white wire from the motor) so you can see it is wired directly into the bus and only puts out 120v. I also put a volt meter on all four of the bus blocks and all read 120v.
Thanks again for any help.

brando1118 · 06-02-2010, 07:14 PM

Houston: You win. I did as you asked and the motor sprang to life. Off to pick up a relay. You, my friend, are the HVAC/Electricity YODA!
Thank you!!!
-B

yuri · 06-02-2010, 07:44 PM

He gets lucky sometimes. Yuk Yuk.

brando1118 · 06-02-2010, 09:01 PM

Yuri: Well I'm glad he did! But I still don't understand it. I had 120v power coming from all three wires that are connected to that relay!! WTF? Is the relay supposed to send an extra 120v to either the red or black wire to make it 240v? Confused.

yuri · 06-02-2010, 09:42 PM

Yep. The white is 120 volts hot constantly and the additional 120 comes from the relay. You were getting a backfeed thru the motor windings and reading it to ground. Gets REALLY tricky when we have to trace wiring and voltages thru the electric elements and sequencers. In the Great White North we can have 6 rows of elements (30 kilowatts) and several interlocking relays and sequencers. Not something a guy learns overnight and can get killed troubleshooting as it has to be done powered up with live voltage to everything.

You may want to think about a new airhandler soon as when those elements short they can start the wiring on fire before a fuse or breaker blows. They are very brittle now and ready to short out soon.

brando1118 · 06-03-2010, 07:24 AM

Thanks Yuri. As with everything in hindsight, it has become clear now. Yes, my air handler is 36 years old. I know it's time to replace her. I try to keep a close watch on the wire condition. I've already replaced some of the wires that were burnt over time. I know the end is coming soon for the old Rheem.
Thanks again for the help.

yuri · 06-03-2010, 07:39 AM

Yep. It can be a cascading effect when one element shorts/drops to the other elements/overamps and all the wires burn up. Seen plenty of BBQed/roasted electric furnaces in my time.

brando1118 · 06-17-2010, 09:49 AM

Hey guys,
Thanks for the help a few weeks ago. Well, after a few weeks, my new air handler motor burnt out. I noticed early this week that the air flow was decreasing slightly day by day. I woke up this morning with a burning smell all through the house. The wires are all fine, but the motor is toast. I'm going to try the old motor tonight and hope that it works. The old motor was a two speed and the new motor was a three speed motor. I capped the blue wire in the new motor and just wired red to red, black to black and white to the constant and two browns to the capacitor. See pics above for the wiring. Any thoughts as to why I lost the motor after a few weeks? Could it be that the new motor needs to be wired to a three speed relay? My A/C system has no motherboard, just relays. Maybe I just need to specify that I need a two speed motor. The guy at the supply store gave me a three speed motor because he said it's cheaper than a two speed.
Thanks.

Houston204 · 06-17-2010, 11:46 PM

Was your old motor 1/2 horsepower?
What was the FLA on the old motor?
What was the FLA on the new motor?
Did you wire the new relay as shown on your original pic? (Hi speed normally open and low speed normally closed contacts)

brando1118 · 06-18-2010, 12:42 PM

Houston:
The wiring of my air handler is up top. I had investigated that and found no issue. I popped off the lower panel where the squirrel cage is and whaddaya know, my brand new capacitor was bulged and ruptured. The smell of what I thought was a burnt motor was actually the burnt capacitor. $3 later and I was back in business.
Thanks for the response.
-B