[SGL1]

I bought a 2001 Frontier 3.3 auto. Problem is the ac only works sporadically. It works more often than not. But sometimes I can park it then come back 5 to 30 min later and it doesn't blow cold. I turn off the switch and leave it off for a few minutes then it may or may not work again. Drive it next day works fine.

I added freon to it and it doesn't appear to have any leaks. Sometimes if it isn't blowing cold it may start to get cold then doesn't. Could the thermal control amplifier be the culprit?

[CaptainRich]

Many things are possible.
The system could be low, which could result in either the system short-cycling, resulting in loss of sufficient cooling.
The A/C system may be running too long, which can result in evaporator freeze-over, also resulting in loss of cooling.
The themal amplifier could be the fault, but you should consult a local A/C technician to pinpoint diagnosis and verify. Don't waste time and money guessing.
I hope this helps.

[SGL1]

Many things are possible.
The system could be low, which could result in either the system short-cycling, resulting in loss of sufficiant cooling.
The A/C system may be running too long, which can result in evaporator freeze-over, also resulting in loss of cooling.
The themal amplifier could be the fault, but you should consult a local A/C technician to pinpoint diagnosis and verify. Don't waste time and money guessing.
I hope this helps.

Well the thermal amplifier is only a $30 part I could probably change myself. I've already spent $55 having the ac charged and leaks ruled out.