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Hello, since the outside unit runs, we know for sure that the 24vac transformer is OK, and that the thermostat works... if the thermostat works that can only happen if you have 24vac reading between R and C.... therefore you are having a test meter issue, perhaps bad contact with the test probes.... or the meter is set on 24vDC
so far it sounds like a bad printed circuit board at the indoor unit... 90% chance of that.
OR... a bad fan motor or fan motor run capacitor if it has one....10% chance... feel the fan motor, it its hot that would be the problem.
if its not hot to the touch, then its most likely a printed circuit board problem
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