Not a lot of pictures here because i didn't think this fix would be the epic that it was.
The system is a generic International Comfort Products. Inside Trane, Tempstar, Heil and ICP units use a lot of the same parts.
First hot day in a while and wife switches the heat pump to cooling mode and when I get home she complains it is not cooling.
Quick inspection reveals warm air blowing and the outside unit - condenser - is not running when the thermostat says it is cooling. The strangest thing is the condenser outside is quiet except for a fairly loud clicking about once every 2-3 seconds.
The solution was, the solenoid for the reversing valve inside the outside condenser was bad. It was shorted out. Replacing is easy and can be done by opening the unit and removing one nut and plugging in the wires. Cost was less than $15.
Here is how i figured it out...
Google searching doesn't help. So i decide to start swapping parts.
I open the access panel on the outside of the condenser. With my finger feeling i discover that one of the relays on the control board is doing the clicking. My voltmeter shows the unit is getting both 240V and 24V power. The Contactor (relay) coil is not powered, so something is not telling the unit to start.
I decided the control board might be broken and ordered one on ebay for $20.
Heil Tempstar Defrost Control Board 1087952 CEPL130547-01 CEBD430547-02A
Picture of the contactor on the left, and the control board on the right.
When it comes i swap it in. Now i have 24V power. Thermostat is working again. Outside the condenser is clicking again. A week with out cooling and a total fail. I'm right where i started.
At this point i got lucky. I played with the thermostat and find that the unit will heat, but not cool. That is the big clue. Googling that problem i find quickly that the reversing valve is likely the issue.
This valve is inside the the outside unit. I have to take the top off with the fan and reach down. The reversing valve looks like this. I didn't take a real picture, this is generic picture. On top is the solenoid. When I disconnected the wires from it, the clicking stopped.