I have a 2000 Express 1500 Conversion with the 5.7L and tow a 7000# camper. Under load, I lose air conditioning, or, at least, out of the dash vents. I understand this may be due to a vacuum operated blend door. Is there a way to fix this issue? Also, does anyone know if I would also lose the rear a/c under these conditions? It appears that I do, but it may be an unrelated problem. I would appreciate any help. Thanks.

 

get a vacuum reservoir, a vacuum "T", and a one way check valve. Find the hose under the hood that feeds the HVAC, cut it, add the "T" and check valve so you don't lose all that precious vacuum while the vehicle is off or under load, and hook up the reservoir

 

Thanks, good idea- I'll try it.