Heater Help!!

[Scrap man]

My heater control only blows in the medium 2 position and on high it doesn't blow at all and the low and medium 1 position barely move any air. I have replaced the blower motor, resister, blower relay, and the selector switch. Need to find the problem cause the wife is freezing to death lol.Any help would be appreciated. Thanks

 

[obijuank5]

Just pop a new fuse in it. Crazier things have happened. That's the only thing you haven't replaced.

 

[Scrap man]

update checked all fuses and they are good also removed the blend door cover and found a bunch of insulation looks like a mouse made its self a nice home. But when changing my controls from floor to vent or and other position the door doesn't move. Seems like a vacuum leak. Where's a good place to start my search

 

[diesel4me]

Seeing you replaced just about everything,the wires themselves are the only thing left,and it's possible the mice chewed them ,and may have cut them in two...double check the resistor and see if any power gets to all 3 taps on it...high speed is controlled by the blower relay,the other speeds are controlled by the resistor..

The resistor can "burn up" if the heater box was clogged with mouse nest,it needs the fan blowing on it to keep its temperature within limits..(seen a few trucks burn up when the resistor started the mouse nest on fire before !)..

That mice nest stuff can be deadly to humans,I'd remove it all and use some type of disinfectant to kill any lingering viruses that might be in the heater ducting..sometimes the mice build a nest on the firewall side of the heater box too,not just the other side under the dash--that has to be removed for air to flow thru the heater core--on square body trucks you can usually gain access through the blower motor "hole" and use a shop vac & vaccum up all the crap out of there..to clean the other side may require removal of the heater box under the dash..

You'll have to start at the engine where the vacuum supply comes from the intake manifold,back to the "bowling ball" storage tank,if it has one on the firewall,then into the cab,where the hoses connect to the selector switch,then down to the vacuum cans that operate the flap doors inside the heater box..make sure the hoses aren't cracked or melted anywhere,that vacuum is actually present at the engine source,and after the "ball" thing on the firewall,then go from there--.

 

[1975Jimmy]

Seeing you replaced just about everything,the wires themselves are the only thing left,and it's possible the mice chewed them ,and may have cut them in two...double check the resistor and see if any power gets to all 3 taps on it...high speed is controlled by the blower relay,the other speeds are controlled by the resistor..

The resistor can "burn up" if the heater box was clogged with mouse nest,it needs the fan blowing on it to keep its temperature within limits..(seen a few trucks burn up when the resistor started the mouse nest on fire before !)..

That mice nest stuff can be deadly to humans,I'd remove it all and use some type of disinfectant to kill any lingering viruses that might be in the heater ducting..sometimes the mice build a nest on the firewall side of the heater box too,not just the other side under the dash--that has to be removed for air to flow thru the heater core--on square body trucks you can usually gain access through the blower motor "hole" and use a shop vac & vaccum up all the crap out of there..to clean the other side may require removal of the heater box under the dash..

You'll have to start at the engine where the vacuum supply comes from the intake manifold,back to the "bowling ball" storage tank,if it has one on the firewall,then into the cab,where the hoses connect to the selector switch,then down to the vacuum cans that operate the flap doors inside the heater box..make sure the hoses aren't cracked or melted anywhere,that vacuum is actually present at the engine source,and after the "ball" thing on the firewall,then go from there--.

For the high-speed fan problem. If you look in the engine compartment on the firewall just above the distributor, there is an electrical junction and a thick red wire with a plastic inline fuse holder. If that fuse is blown, you won't be able to activate high fan speed.

Also, depending on where the critters came in from and how far they got into your truck, I would maybe start looking at the main vacuum feed for the heater/ac system that passes through the firewall on the passenger side. It should be connected to a vacuum canister in the engine compartment next to the evaporator. If that is intact and the vacuum canister holds vacuum still, I would then move into the cowl. There is a vacuum activated air diverter in the cowl that closes off the fresh air intake to the AC system and works in conjunction with the passenger kick panel air-circ door. If both are in tact, then it's likely the critters ate up your vacuum lines under the dash, and you're probably in for a bit of a headache...