I have a 99 blazer LT with auto climate control that worked fine until I took it in to have an intake gasket replacement, lifters replaced as one was sticking, a tune up(plugs, wires, rotor cap). Before I left the mechanic I told him that it had worked perfect before hand and he said it was a coincidence. Is this so? Is there something under the hood or electrical that he might have disturbed or left unplugged? Here are the other coincidences, it started to not start easily so I took it to a chevy dealer and they found the distributor was off twelve degrees and a vac hose that they noticed was 'just unplugged' had a bolt put in it for free by them(I found where it attatches to the wheel well but don't know what damage this could have done), I took it back to him and he said he found a loose sparkplug from his work and now it is harder to start and the check engine light is telling me the timing is off!! I would love as much insight to all my issues since he has worked on it!

 

Much of the HVAC system is operated by engine vacuum. If the vacuum lines are not connected properly to the engine, it can cause problems. However, if it is cycling from hot to cold, it could be a coincidence as this is controlled by an electronic actuator that operates the temperature door. You should try to recalibrate the system though.

As far as your other problems, what is the specific code. If the timing is off, it is his fault...