'00 Sonoma A/C Issues

[Austin4820]

I have a 2000 GMC Sonoma SLS Ext. cab.
When I bought it about 6 months ago, the A/C only worked on the two highest settings; 3 & 4.
Since I got it in the middle of a freezing cold winter, I wasn't too worried about using the A/C on any low settings.

Recently, it stopped working on the highest setting. So, now only 3 works.
Also, the switch that's used to select the different modes like defrost and Max A/C, doesn't work properly. In the off position, the A/C turns off. In every other position, it turns on the regular upper vents.

Any help would be greatly appreciated.
~Austin

 

[Jet Mech]

AS far as your fan/blower speed goes I would say your switch is on it's way out. Your mode selector is vacuum controlled. I had this same problem on my 2000 Sonoma. Turned out to be a cheap fix. All it was is a rubber elbow connecting the hard plastic lines had dry rotted. The location of the connection was right over the power brake booster. If thats not problem I would continue looking for vacuum leaks. Good luck.