I a 10 year Ruud heat pump UPMC-036JAZ condenser that has no 24v signal at the contactor. The compressor and fan work when I depress the contactor. My defrost board is a Rheem 47-21517-11. Can someone tell me what voltages should be at what terminals when the T-stat is calling for heat?

Thanks in advance.

Small red button down by the refrigeration lines going into the outside unit. Give it a push to reset. It's a high limit reset button and is known to go bad.

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Originally Posted by T-Top

Small red button down by the refrigeration lines going into the outside unit. give it a push to reset. Its a high limit reset button and is known to go bad.

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Thanks, but there was no status change. I felt a click when I pressed the button. My board is a Rheem 47-21517-11. Across the top are the following lugs: C, C, D (O?), Y, B,R. Down the left side: Y, CC, RV, C. On the right (alongside a relay?) are 2 lugs titled FAN. The top left "C" has a purple wire that is not connected to anything.

With the T stat calling for heat, I get the following readings across the top row, using the second "C" as a presumed common: D=1v, Y=26, B=26, R=1. On the left, using C as a presumed common: Y=26, CC=0, RV=26. Between the common and the FAN=0.

With no call for heat, I get the following:
D=10v, Y=7, B=27, R=27. On the left, using C as a presumed common: Y=7, CC=0, RV=27. Between the common and the FAN=0.

BTW, I got these readings with the 220v breaker off, and the contactor removed. Also, did I respond to your answer in the correct manner? This forum is set up different from a consumer forum when it comes to replies. Again, thanks for your advice.

Bill

R to C should have 24v all the time heat calling or not. That's what runs the logic in the control board. With out a true 24v the board will not work.