Warm air blows out of the A/C?

Symptoms: A/C has gone in and out over the last week (mostly out). Compressor is not engaging. Refrigerant is full.

Here's what I've done:

I have replaced the low pressure cycling switch.
I have recharged the system.
I have replaced every o-ring that I can get to.

Here's what I've tested:

I powered the compressor with a small 12v battery. Compressor worked fine and allowed me to recharge the system correctly.
I've tested the low pressure cycling switch for continuity past the connector. Switch and connector are fine. I do not get 12v on this wire when I turn on the A/C.
I've tested the high pressure sensor. Reference (5v), signal (1.3v), ground (good). Voltages are static when A/C is on or off.
The fuses and relay are fine.
I do not know how to test the climate control unit.

How would you proceed?

Air Conditioning problem
2006 Mercury Mountaineer V8 Two Wheel Drive Automatic

The rear AC only blows warm or hot air, while the front AC blows cold. Neither refrigerant line to the rear evaporator is cold, or hot. Pressure readings on the system are normal and steady.

Thanks for the response. In your picture, is this valve mounted on the side of the evaporator inside the left rear quarter panel, or is it inside the connection block underneath the left-rear corner of the car?

The AC started blowing hot air about 2 weeks ago (i noticed the compressor didn't "click" when the engine is started. So I turned the AC off for approx. 2 days & then I just happened to turn it back on & it blew COLD air. Then 2 days later it went back to blowing hot air. So, I repeated the same scenario & after 2 days, I turned the AC back on & it blew COLD air for 6 days. But, today it went back to blowing hot air again ! I checked the pressure to see if I needed to add refrigerant but the guage said the pressure was in the "Red - Warning" range (approx. 110 !). Any idea why the AC compressor keeps kicking in & out like this? Thanks.

I have heat when I have it on face or floor but no hot air when I put it on defrost and the rear ceiling vents don’t blow hot air either.

I have a 2002 Mercury Mountaineer and my cigarette lighters (ac power not actually using the lighter just chargers etc.) Have not worked since I purchased the car. I have checked the fuse that was listed in the owners manual to be the fuse for them and it is a good fuse. What else may be the problem?

I took apart what I could to get to the back of the outlets and all (2) of my outlets have power connected to the back of them but I found this wire in the front of my center console that has a plug on it but is not connected to anything. See attached photos to view the plug.

I also meant to say that the outlets have a wire plugged into them I am not sure if that wire is actually hot or not that is what I was wondering about this plug

A/C is turning on and off repeatedly

My AC is not blowing out the vents, it has a new blower motor and AC has been charged.