HVAC - almost made it through the summer

[gr8fl4porsche]

Still hot in St. Lou

102 today - summer is not over yet.

AC crapped out last night

Compressor was humming and condensor fan would not spin and motor was very hot.

So I changed out the motor and capacitor. Here is the result when I flipped on the thermostat. New capacitor appears to have blown instantly.





Wiring at compressor looks good. Unit is 6 years old.




Old capacitor was dead and had similar discoloration near the compressor post like the defect in the new one.




Would a locked up compressor burn out a new capacitor like that or did I wire the replacement motor wrong.

Wires from motor (AO Smith)
Black wire to left side of contact switch, yellow wire to right side (the side with the pull), brown to 'fan' on capacitor and brown/white to to 'common' on capacitor.

I checked that the capacitors are similar.

[turbo6bar]

Use a multimeter to check if you compressor is grounded. Remove the black, red, and orange, and check each to ground. If any shows less than 10 ohms, your compressor is toast.

However, you say the compressor was humming, so it sounds like it may be working. Did you get the right cap to match the new condenser fan motor?

You're shorting out somewhere, but the condition of the compressor terminals suggest the problem is not the compressor itself.

[gr8fl4porsche]

I will check in the morning concerning the match between the new motor and new cap.
The new cap matches the old one and the Johnstone rep had my new motor info when he picked my new cap. Will double check.

I am heading out to check the compressor leads.

[gr8fl4porsche]

On compressor

C to R = .001
C to S = .002
S to R = .003

Looks good

Found a good ground and received no readings on any contact via my cheapo multimeter.

I assume thats a good sign?

[MBAtarga]

Originally Posted by gr8fl4porsche

On compressor

C to R = .001
C to S = .002
S to R = .003

Looks good

Found a good ground and received no readings on any contact via my cheapo multimeter.

I assume thats a good sign?

It means it wasn't shorted out by a lightning strike like the compressor on my basement unit's heat pump was last spring!

[billybek]

Good sign no shorts to ground but if your measurements are accurate and represents ohm value from winding to winding, you have a bit of a problem.
Interesting enough, they do add up. Run to common + Start to common should equal Run to Start.
Did you take these readings with all the wires off the terminals at the compressor?

[gr8fl4porsche]

Yes wires were off compressor. Multimeter is very cheap - probably not very accurate. Will test in the morning with a better unit. Anything else to test?

[billybek]

No not yet. Just recheck the compressor motor and the condenser fan motor.
I never liked those capacitors that do both condenser fan and compressor.

[turbo6bar]

Those readings, if in ohms, seem really low. My low-end Fluke doesn't read ohms to three decimal places. It's been a while since I read ohms across the terminals. I recall numbers around 3 to 5 ohms, though???

If the terminals aren't grounded, I think you are safe. Check the wiring to ensure there is nothing shorted.

[rick-l]

He is probably reading 0.001 kilo ohms or 1 ohm and probably not very accurately.

[gr8fl4porsche]

Thanks for the help gentlemen!

House is cooling nicely.

I ended up installing separate caps. The new motor did not like the dual cap.