On my 2005 Silverado 2500 4 wheel drive diesel when driving with the AC on it will at time start blowing hot air instead of cold. sometimes from the drivers side only, other time passengers side or both. If you stop & kill the engine and restart it it will go back to operating normal .

 

Hey Don, mine is doing the same thing... did you ever find the problem?

 

Some control under the dash solved the problem with the heater coming on while driving with the A.C. on $400. Changed the thing twice in 1 year! Seems like G.M. should have had a recall on this!

 

Thanks Don, there's several things that could have been recalled on this 05'!