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Old 11-20-2011, 02:39 PM   #1
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Old Rheem Air Blower Motor Wiring Problem

I have what appears to be a very similar setup to this post:

Air Handler Motor Wiring

Please forgive my long post, but did lots of reading and wanted to give as much info up front since I am asking for help. And being a network engineer for 26 years I try to be specific since I am always being asked vague questions.

But my motor is the original. It was doing a thermal shutdown when I started using the heater this winter. Since the AC fan speed worked fine for the last 31 years (I know!!) and the heater fan speed worked till this winter I pulled it out, checked the wiring and could not decide what the problem was. Since it was the weekend (of course) and we had a cold snap I had to do something to get up and running. I found an old 110v, 1 speed motor in the shop that was also a FRAME 48Y and swapped it out with the 240v 4 speed motor.

After pulling the motor and getting on the bench based on my reading on this site and others I assumed the problem was a bad run capacitor so I ordered a new one from Mouser. It came in and now it is hot and humid this weekend (central texas weather is always a crap shoot) and I replaced the old capacitor with a new one - 5 u, 370V ac. The old one had no markings at all so I made an educated guess based on the motor speeds, RPM, HP, Voltage.etc.

I went to test the motor out and the way I *think* (sigh.. I know) it was wired does not seem to be very happy. It runs on high speed (I am using the "FAN ON" to test) but gets hot. I have tested everything and every combo of things I can think of. I wanted to get some opinions on how it *should* be wired (it was wired for 2 speed before) with my EMERSON K55HXJFA-5105. No diagram on the motor and the RHEEM service plate has lost 1/3rd of the schematics, of course the part with the blower motor wiring is missing. I have searched crazy mad over the net for pinout/diagram for the motor, but no love.

Here is the motor plate:
Old Rheem Air Blower Motor Wiring Problem-motor-panel-custom-.jpg

This is all the wires of the motor, shown with new run capacitor in place:
Name:  all motor wires (Custom).jpg
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Here are the 3 wires to the motor from the air handler :
Old Rheem Air Blower Motor Wiring Problem-wires-air-handler-custom-.jpg

I did some OHM testing of the motor with the new run capacitor based on several documents and a couple of youtube videos. Here are the results in a table:
Old Rheem Air Blower Motor Wiring Problem-ohms-1-custom-.jpg

Based on several questions on this forum to posters here are some additional voltage tests.
This is every voltage combo I could think of from the 3 wires to the motor with AC and FAN on:
Name:  AC-FAN voltages (Custom).jpg
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And this is HEAT and FAN on:
Name:  HEAT-FAN voltages (Custom).jpg
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Size:  11.4 KB

I have 3 houses out on the compound right now with more to come. I realize I might need to buy a new motor, but I still want/need to learn how to trouble shoot these either way. I have several other pictures but I hit my 6 attachment max, so please let me know if there is something else I can add to this.

Thanks in advance!


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Old 11-20-2011, 02:56 PM   #2
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The two capacitor wires are usually brown and brown and white stripped and come with spade terminals attached to them so they are pretty much unmistakable.. The rest are the speed taps. Black is usually high (for cooling) and red is low for heating mode. The other wires are medium low and medium high and are usually parked on the baord.


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Old 11-20-2011, 03:41 PM   #3
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I should be a bit more clear in one thing. The picture called

"Here are the 3 wires to the motor from the air handler :"

Is where I did the voltage testing, not with the motor online.

The OMHS table I posted is for the motor with all the wires pictured not connected to the power.

I am comfortable with the capacitor connections because I just plugged like to alike when I replaced it. What I am struggling with is when I use the motor black connected to the wire harness blackish/blue I get high speed but the motor gets really hot, when I connect to medium or low it turns but gets really hot really fast so I won't leave it like that.

I am resigned to replacing it, but I still would like to understand the sequencing of signals from the blower unit relays.. why is there 80V across red-black, why does the red-orange voltage go from 28V to 110V when I go from having the AC signal the motor to run to having the heater signal the motor to run. Could the 110V be my heat problem.. to low voltage?

I am comfortable tearing the motor down and getting into the windings, since it is a 4 speed motor and the unit only appears to signal for 2 speeds, I was thinking I could limp it along for the winter while I scope out a replacement unit on the cheap. Any ideas on that?

Last edited by CompoundNetwork; 11-20-2011 at 03:44 PM. Reason: adding to it the end...
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Old 11-20-2011, 03:51 PM   #4
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run themotor on hi speed and see what amperage it draws....when no load attached to motor,amperage should be well below name late...
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