I have a 2007 PT base model that has always had great ac. Recently, past several months, I heard a pop sporadically when turning on the ac only but it still blew very cold. A few days ago I put on the air and heard the pop and while air is blowing it is not cold. This occurred after a tune up by an independent shop. I can hear the compressor going on and off. The dealer wants $130 to diagnosis and an independent shop wants $125 to put in R134 and check for leaks and then go from there?

Any ideas what if might be and what I should check?

Car have 89K miles on it.

 

If your high-side pressure is spiking it could be bad radiator fan motor, or a bad fan relay.