Hi,

The AC in one my rentals would not come on so I checked all the wiring to see if something was loose, it wasn't. I crossed several combinations and when I plugged the blue wire to the Y terminal the system shut off completely. I bought a new heat pump thermostat but once plugged in, it says "No AC Power". I put the old one back on and nothing happens. I checked the outside unit by pressing the reset button and it comes on but as soon as I release the reset button, it goes off. The Air Handler is located in the attic and I have turned all possible circuits off and then on again trying to reset the Air Handler, but nothing happens. Is there a fuse or reset button that is internal to the Air Handler? What is wrong with my system?? The wiring on the Air Handler is as follows: R-Red, C-Blue, G-Green, W-W2, E-Black. The Air Handler is a Intertherm. Any help would be appreciated.

DE

Seems the low voltage control transformer may have been or is now defective, as indicated by the "No AC power" error. You will need a volt meter that can handle 24 volt up to 240 volt. Find the control transformer and test both the line side which can have either 120 or 240 volt, and the output side for 24 volts.

You state the unit would not come on, then crossing the blue to the yellow caused the unit to shut down completely. If it shutdown completely, what was running?

The outdoor unit coming on proves there is line voltage present. There can be a reset button directly on the fan motor of the air handler.

Best to start cheking all the units for at least line voltage, then move onto finding and checking the low voltage transfomer.

tkrussell,

Thanks for the reply. Prior to the crossing of the wires, the unit would come on, but would not cool. Once I crossed them, everything ceased. I will look for a reset on the fan motor and test the wires to see what happens.

DE

Crossing the yellow and blue shorts out the control transformer. You may have burned it out or if lucky, blown a fuse. If the thermostat also controls the heat or has a fan only option, try them. If they come on, the transformer is OK, and the fault is in the A/C somewhere.

If the air handler was running, but the compressor and outside fan weren't, the relay may be bad. The Y and C terminals should be connected to the relay coil. When the thermostat switches 24 V power to the Y terminal, the relay should operate supplying power to the compressor. The air handler should have its own relay.