After about two hours of highway driving the car's AC seems to slowly lose its "umphf". Not much cooling and I Hank a reduction in fan speed. After I turn it off and drive for 15-20 min and start it up again. I'm good for a while.

Is it freezing up or is there something else going on?

 

First, the HCH2 seems to be very conservative on its auto setting. When it reaches the set point, it seems like it nearly shuts down. It sounds like that's what you're describing. Try adjusting your set temp down a few degrees.

Second, when it's 85-95°F ambient, put the A/C on fresh, full blast and 65°F with doors open. Check your sight glass for bubbles after 5 minutes of operation. If you see bubbles, you're low on R-134a. It is safe to add straight R-134a ($4.88 SuperTech brand from Walmart). Make absolutely sure there is NO sealant, NO oil and NO dye.

 

Was not using auto setting. I should have explained that. Sorry.

My ignorance is about to become very appearent. I have no idea what or where a "sight glass" is.

As for the procedure, I can do it but here in Wisconsn the 85 degrees are likel gone until next year.

 

Ah well.. why are you using air conditioning, anyway...?

Under the hood on the high pressure A/C line, there's a little block with a sight glass on it. If it's low, you'll see bubbles or what looks like water flow when dispensed by an aerating nozzle. When it's not low, there is nothing visible but the inside of the block.