Nissan Repair: Nissan A/C intermittently blowing hot air, thermo control, control amplifier

Question
I have a 97 nissan XE pickup. A/C has worked great for years and has never been serviced. No freon has ever been added since I purchaced it new. Recently it has been started blowing hot air some times but will go back to blowing cold. When it's Cold it's really cold. Today when it was blowing hot I conncected a gauge to the low pressure side and it show 110 psi, the clutch was not engaged.I've seen on a lot of sites that the dealers guess which parts to replace with no progress, others have said it's a Thermo Control Amplifier. Please help.

Answer
Zeke,

I would get a set of gauges and look at what the high side is doing.  But, from what it sounds like is that the pressure is so low the compressor will not come on.  You probably need to have it evacuated and charged.  There is a cycling switch that contkrols the compressor and there is an expansion valve, under the dash, with the evaporator core.  But, from the low side only it sounds like it needs to be evacuated and charged.  If you can get a full set of gauges and get the high side number to me we would know for sure.