Sometimes when I start the truck it blows warm with the A/C on. Probably low pressure, I'd guess. How can I test the switch? If I switch off the A/C or the engine and then turn the A/C back on it cools. Weird, huh?
So, I have taken to starting the truck and then starting the A/C, which works but makes me wonder.

I'm thinking of having an evcuation & recharge to see if it has a low charge, the shop I used to work at can measure what they pull out and replace for me. Am I overdoing this? Or am I saving my compressor from running without enough lubrication which is what happens with low rfrigerant charges.
I am a tool and chemical rep, we sell A/C tune up kits which give a 4 oz hit of R134, some A/C dye and a little oil. I'm leery to do this because when I worked in the desert the A/C guys always drilled us to use exact quantities. Any real A/C experts on here?

 

Well I have the same problem. Does your truck seem to take a while to cool down as well. Also mine when you put on recirculate seems to maybe get warmer?

 

Yup. But now that it is warmer weather it chills every time I start iit up. I'm guessing the charge pressure might be low causing the low pressure switch to keep the compressor off. Can I read the switch with a Volt Ohm Meter?