Blower Motor,interesting problem

[72kool]

This morning i started my truck to warm up before work. i go outside after 15 minutes and it doesnt feel too warm in the cab. Not a big deal because it didnt frost over the windows. I felt the defrost vents and nothing.. i start driving to work and it starts blowing out the vents just fine. ok no problem i think. I get to work and check it when i park, no air through the vents again. Now the heat works well when it works. I have replaced the radiator and heater core and all hoses, all withing past 2 years. heat worked fine this spring without an issuse. it doesnt seem to have any coolant issue, just air flow issue. what would cause this? is it a voltage issue where the blower motor doesnt get enough to engage until im driving?

[haysonj]

Originally Posted by 72kool

This morning i started my truck to warm up before work. i go outside after 15 minutes and it doesnt feel too warm in the cab. Not a big deal because it didnt frost over the windows. I felt the defrost vents and nothing.. i start driving to work and it starts blowing out the vents just fine. ok no problem i think. I get to work and check it when i park, no air through the vents again. Now the heat works well when it works. I have replaced the radiator and heater core and all hoses, all withing past 2 years. heat worked fine this spring without an issuse. it doesnt seem to have any coolant issue, just air flow issue. what would cause this? is it a voltage issue where the blower motor doesnt get enough to engage until im driving?

Sounds like loose or dirty connections on the blower motor under the hood or a faulty switch at the dash. also check the ground wire on the blower motor. I believe there is also a high speed resistor over behind the glove box that could also be the problem

.

[Chevy 350 Fan]

Does the Amp meter work? if so what does It read? Does it start blowing if its sitting and you rev the engine a little? does it still blow when you come to a stoplight? I remember my old blower motor had a bad bearing and it would sound god awful sometimes and just fine other times. Eventually it got to the point where it would only work about 1/2 the time lol. I changed it out and had no problems. (maybe $15-$20 at auto zone but its made in china!) its kind of a pain in the ass because you have to take off the passenger hood hinge. I tied my hood to a hook in the ceiling with a rope so I wouldn't need to take it all the way off.

[Dave in Ozark]

Could you hear the motor running? Perhaps a low vacuum at idle keeping the damper from diverting up to the windshield?

[Jrainman]

Sounds like a ground issue , but could be switch . as stated check connections , then if connections seem good add temporary ground wire to one of the blower motor through bolts rite to your negative terminal on the battery . if that works then just make up a new ground to body if not move on to the switch it self .