No Heat!!! Blower Won't Blow Air Out Of Vents! Please Help I'm Freezing Down Here!

[The White Noise]

I have an 88 Comanche 2wd 2.5l 4 speed and idk why but the heat doesnt blow anymore? I've replaced the resistor, replaced the blower fuse, idk what's goin on. My vents don't open either when I change my control to vent ( I have my dash out so I can see that the door isn't open) someone please help I live in ga and its starting to get cold down here (I'm not really a cold person) and the truck is my daily driver.

[cruiser54]

Is the heat going out the defroster vents?

[Comanche County]

Heat going to the Heater core and the vent door are both vacuum controlled. Look on the passenger side of the firewall and find the heater hoses. There's a bypass valve that allows coolant into the heater core. Find the vacuum line that goes to the valve and follow it and ensure there are no cracks or leaks. Also find the vacuum ball under the passenger side of the front bumper and do the same.

 

Next, operate your temp slider paying close attention to the way it feels. Can you feel any pressure when you actuate the slider or is it completely free? Sometimes the back portion of the lever can pop out of the cable so it looks like its on hot, but its still cold as can be. The fix is some creative bending on the slider arm. 5 min minutes and a #2 phillips and you can have that fixed. This is what mine is doing now.

 

I had an XJ that for some reason would always melt the fan speed slider, when I get an MJ or XJ its one the checks I do, just remove the temp assembly and make sure the wire connectors aren't fried back there.

[The White Noise]

Yes the heat blows out the defroster but very lowly, the speed control doesnt do anything? And I'll check the lines and get back with u later. Hope we can figure this out! Lol

[Eagle]

Slow down, and help us by giving enough information to diagnose. You may have more than one problem.

 

First: the blower. Does the fan run? If the resistor pack is bad, it should still run at full speed with the control is moved to HIGH, because the resistors reduce the speed. High speed doesn't go through a resistor, so that should always work even with a blown resistor pack. If the blower runs on high, you need a resistor pack.

 

If the blower doesn't work at all, go to the engine compartment side, unplug the connector to the fan, and try hot wiring it with a separate ground and a wire right from the battery. If it doesn't run at all, you need a blower motor. Not a surprise if that's the case -- the motors use brushes, and they do wear out.

 

Second issue is where the air comes out. As noted, the controls are actuated by vacuum. Even a small vacuum leak can stop the heater controls from moving the flappers. The default is to send air to the top-of-dash defroster outlets. If you have a blower motor that works, and the air is coming out of the defroster outlets, you need to look for a vacuum leak.

 

Third is that the Renix years (which includes the '88) have a vacuum controlled valve in the coolant line leading to the heater core. Make sure that valve is functioning (or just bypass it).

 

Last is that the heater core is now 25 years old. It would not be a surprise if it's completely clogged, especially if it hasn't been maintained. You may be looking at a heater core replacement. If the dashboard is already open -- do it anyway, as a preemptive strike. When the heater core springs a leak, it dumps coolant into the passenger side footwell. It's not pleasant.