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I have a service call that has stumped me and another hvac contractor. Carrier split system, heat pump. The low voltage is playing games on us. with the system off em. is showing 24olts at the thermostat. up in the attic at the air handler when I break the two Y wires it shows 12olt on each wire when they are not together. At the condenser I have all the low voltage dissconected. I have ohmed out the wires and there is no short. in short when the thermostat satisfiys there is still 24 volts going to the condenser what can it be? this is the 3rd t-stat this contractor has changed.
 

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Did you ohm out each wire to each wire. Or just each wire to one other wire.

What thermostats are you using.

Is that 12 volts measured from yellow to yellow wire. Or measured from each yellow wire to common.
 

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It's probably too late,but, take the t-stat to the attic with a 4' lead of stat wire. Wire the stat at the attic with the 4' lead as if that was to be the stat location. Do the symptoms continue? If so, take the lead & stat to the hp & wire the low voltage from the hp to the air handler as they should be. If not, then the problem lies somewhere within the wiring to the stat.

If the symptoms continue, I would suspect the culprit lies within the wiring to the h/p. Good luck.
 

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Try bypassing the stat. Jumper the terminals in the air handler, verify that the controlls are good in the equipment. More often then not it is gremlins in the t stat wires, it happens.
 
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