10 yr. old Trane 1000Xe was cooling fine during the summer. It was even checked out by a professional A/C tech, who found it to be working Ok back in July. Two weeks ago we had to use the heat for a couple of days, and then we were able to go with out using the A/C at all for a week. The weather warmed back up and we turned the A/C back on to cool off when we discovered that it would only blow hot air, even when set at the coldest setting. Both Airhandler and outside unit is working, and the comprssor is running too, but I found that both copper lines were extremely hot and that they seemed to cycle between hot and ambient cool. Please help.

Is this a heat pump system?

Yes this unit is a Weathertron heatpump

The reversing valve is not operating correctly in the outside unit. The valve itself is brazed into the pipe with silver braze alloy so it is something you could not change.

Other possibilitys are

Valve stuck
Bad valve coil.
No 24 volt circuit to valve coil

Most if not all heat pump units now days default into the heat mode of operation. Your unit is in the heat mode and the signal is not getting to the valve for it to go into the cool mode.

Thank you so much for the needed advise, I was afraid that it might be a bad compressor. I haven't checked the voltage at the valve coil but I'll be sure to do that. At least this gives me hope that I'll be able to afford to fix it. I will let you know how it turns out. Thanks again