Heater Control Unit Issues

[X~FACTOR]

On my AC/Heater Control Unit the fan switch only works with either off or high fan setting, nothing in between. Also the AC/heater knob blows only the defrost setting no matter which way I turn the knob.

I have already replaced the AC / Heater Control Unit. What other parts can I replace to get this working right?

 

[koda2000]

sounds like you have a vacuum leak somewhere. that's what causes the A/C to only blow out of the defroster vents as the default setting. this would have nothing to do with your blower fan motor though. do you have manual or EATC HVAC controls? the EATC control version often will blow out the blower motor control module, then the motor will only run on HIGH.

 

[X~FACTOR]

I have a manual one. I traced the tiny vacuum lines from the control unit to another junction. It all looks intact but don't know where it goes from there.

 

[koda2000]

eventually all vacuum lines connect to the vacuum reservoir ball in the passenger side front fender, which is connected to the intake manifold. a leak anywhere (even a small one) will cause the A/C & heat to blow out the defroster vents.

if you have the manual HVAC controls, your blower motor's ballast resistor may be burnt out, or the may have corrosion on its electrical connector.

 

[boominXplorer]

Check the vacuum lines running from the condenser box under the hood to the vacuum globe then to the motor. The vacuum globe is in the passenger inner fender well.

The blower motor resistor is the issue for your fan speed. It is mounted on the box in the engine bay below the blower motor.

 

[R1dd1cK]

It has been said already 2 or 3 times. It is the blower motor resistor. Replace that then the fan switch will work like it should.

 

[X~FACTOR]

It has been said already 2 or 3 times. It is the blower motor resistor. Replace that then the fan switch will work like it should.

Thanks!

 

[Turdle]

In case you hadn't seen this yet--

http://www.explorerforum.com/forums/showthread.php?t=192842&highlight=heat+defrost+vent

 

[X~FACTOR]

In case you hadn't seen this yet--

http://www.explorerforum.com/forums/showthread.php?t=192842&highlight=heat+defrost+vent

No I haven't. That explains just about everything. lol. Thank you!

 

[X~FACTOR]

Just an update. I found a broken line leading to the globe. glued it back together and its all good. Happy days again. lol

Checking on the fan switch tomorrow. I found 2 plugs near the blower motor. Checking which one is the culprit.

 

[X~FACTOR]

I replaced the blower motor resistor with a new one. It didn't do anything.

Just to be sure, it is this thing right? It's attached to the bottom right of the actual blower motor?

 

[koda2000]

yes, that's the blower resistor. depending on the fan speed selected it routes the current through the resistance coils in various ways to reduce the voltage and therefore motor speed. on HIGH there is full system voltage going to the motor so it runs at full speed.

if the problem isn't the resistor, then there may be a switch/wiring issue or a possible blower motor problem. use a VOM to test the output voltage of the resistor. as example, low may read 6 volts, medium may read 9 volts and high will be 12 volts. if the motor is worn out and binding, it may only spin when it gets 12 volts.

 

[X~FACTOR]

Ah got it. Thanks man.