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?
Pressure readings could help diagnosis. Having correct charge(by weight) is critical,next time it blows warm with AC on open hood and see if compressor is engaged. Must admit I do not know a component named thermal control amplifier.
I’ve been having the EXACT same problem with my 2000 Altima. The Nissan dealership says I need a Thermo Control amplifier switch too. But what exactly is this part and what does it do? It was explained to me but I forgot. I have tried searching this part online and haven’t been able to find anything. Is it called by any other name? Just like the other person that replied, when I asked a couple of guy friends (who know more about cars than me) they’d never heard of it either. The dealership is asking for $245 plus tax to fix this part and I’m wondering if this is a good price, that’s why I wanted to do some online research first. Anyone familiar with this, Please help!!!
I agree that knowing the pressures is critical to determining the problem. However, there is an item called a thermal control amplifier that could be the problem and it’s not that rare a fault. It would require either an ALLDATA subscription, the factory manual, or the ability to follow a good electrical schematic to properly diagnose that little item.
Other modern vehicles use similar widgets as controls but may call them by different names. For instance, Mitsubishi uses a similar item and it’s referred to as an automatic compressor ECU.
In older, simpler times a plain old wire did the job just fine. 
They called it the same thing on my 1990 Toyota P/U. It is an electronic control module that monitors the evaporator temperature, and controls the compressor. Mine was located behind the glove box, and had a temperature adjustment and wire harness on the front. Mine never broke, but I did have to adjust it once when it was running a bit warm, but everything else checked out.
Thanks a lot. One more question though. I was trying to do some more research and found that sometimes it can be something called a “blend door” also. I know in my case the dealership says it’s the switch. But I’m just curious…how do you know whether it’s the blend door or the amplifier switch???
You would need to pop the hood, look at the compressor, and make sure that the compressor is running.
If the compressor is working properly the A/C lines out of the firewall should be cold and possibly sweating if it is humid in your area. There should also be a condensation drip underneath the vehicle on the passenger side.
If the comp. is running along with cold lines and a condensation drip but hot air is being blown anyway then it could very well be a blend door problem.