No High on ftront HVAC blower..

99 Suburban K1500 w/5.7. The three lower speeds work, but the front blower does nothing when switched to high. What could this be?

Also, while I'm posting, the outside air blend door is getting flaky. Is it a vacuum diaphragm down there, and how hard is that to change out?

Thanks

Blower motor: When you switch to high a relay is pulled in to supply a full 12v to the blower. So it could be any or a combination of 3 things. The fan switch, the relay or the #3 50a BLOWER fuse in the underhood fuse panel. Relay is located on top of the heater plenum behind the glove box.

Blend door: Is most likely electrically controlled and the issue could be debris blocking the door from full movement.

Thanks for the quick reply, stickman. I had checked the underhood fuse earlier, and it was okay.

I pulled out the glovebox, fiddled around with the blower connections, and tapped on the relay. Next key cycle it worked fine.

Intermittent electrical problems are my favorite. :runaround:

I haven't checked the blend door yet.

Thanks for the quick reply, stickman. I had checked the underhood fuse earlier, and it was okay.

I pulled out the glovebox, fiddled around with the blower connections, and tapped on the relay. Next key cycle it worked fine.

Intermittent electrical problems are my favorite. :runaround:

I haven't checked the blend door yet.

could be the relay contacts are worn. highest speed is the relay ..lower speeds the resistors.

I would guess the relay..

at this age and use , the blower motor will have worn internal brushes. as these wear down the motor will no longer run. the motors also when old , draws more current , as they are less effecient.