I had the same problem- BAD A/C Pressure Switch
Hummer H3 A/C Pressure Switch Original 18797KNSH 2006 2007 2008 2009

 

I put the A/C gauges on my 2008 H3.

It showed that the high side pressure was about 125 psi -- About half what it should be. I couldn't put any freon in because I didn't have a can adapter for the new R134a cans with the built-in valve.

Next day, I bought the correct can adapter, and was able to get the pressure up to about 250 psi.

However, when I took the gauges off, the low pressure side was bubbling up oil and leak solution. It stopped in a minute or two, and I put my finger over the top to verify that it wasn't building up any pressure.

The high side was much worse. When I removed the quick disconnect, I had a "Blowing leak". I noticed a small piece of rubber inside the valve. Using a awl, I was able to open the valve, and slowly blow the piece out. As soon as the debris was out, the valve seated correctly. The only questions are what seal is shedding bits into my freon, and what happens when a bit of debris hits the expansion valve?

In running a number of errands today, it did seem better. If I was slow/stopped in traffic, it still seemed to not cool as well, but I didn't get that feeling of a significant increase in vent temperature or humidity.

I don't usually use Recirc mode, but in this weather, I just don't think it is reasonable to ask it to drop the air temperature that much. When I hit the Recirc button it was comfortable for the rest of the trip home even while stopped at a light.

 

The rubber did not originate from inside the system. The high pressure valve has a rubber shroud over the ball from the factory. if you screwed the high side valve in too far when opening the port I think its possible to entrap the rubber piece in the ball seal. My high side also had a bit of a leak after I did my work but I “burped” the valve and then it seated properly with no residual leak.