Could you please help me with an A/C problem?
When I start my full size 1993 4x4 Chevy Blazer, the A/C delays up to 10 minutes before the blower will work. None of the fan speeds will blow. After this delay it starts blowing normally. This only happens about half the time. This happens even if I have the A/C off before I start the engine. I thought it might be a relay or something. The dealer will not guess what it might be without leaving it with them. Please let me know your expert opinion.
If it were a constant problem we could track down the cause pretty quickly with the appropriate wiring diagram and a 12 volt test light. But this one is an intermittent electrical condition which makes it a bit more difficult to diagnose.
I've taken a quick look at the wiring diagram of your Blazer's blower motor circuits. The system uses a solid state A/C controller unit. That's the box mounted in the dash with the fan buttons and temperature control lever. The system is using separate relays for each fan speed. So that eliminates these relays as possible causes, seeing that all speeds are not working when the problem occurs. This leads me toward the problem being a main power source or ground to the blower.
Here are some choices. Number one: It may be the motor itself coming and going. Number two: It could be a bad connection somewhere (ground wires, junction blocks, connectors etc). Jiggling the appropriate wiring harnesses and listening for the blower to stop at the same time is a good way to locate a bad connection. Last but not least, is the A/C controller unit itself.
Next time you start the engine and the fan doesn't work, give the dash a shot with your fist, right in the area of the A/C controls. Not too hard. If the motor starts on impact the problem is either the controller or a connection in the immediate area. Chances are it will be the controller. It's a fairly common failure on this particular model.