My climate controls in my 1998 don’t work right, it appears to be stuck on heat (or maybe my air conditioning is blowing hot air?), and the vent speed controls don’t work. The previous owner appears to have jerry rigged something, normally, the vents are just barely on, no matter what the switch is set to, they cannot be turned off either, but a switch has been wired into the glove box that when flipped puts the vents on high, but the speed still cannot be adjusted or turned off. The blower motor appears to have been serviced at some point, and the wiring for that switch is spliced into the wiring harness on the blower motor. The vent controls work fine and the buttons appear to work too. The climate controls are the computerized type.

To review:
The vents always blow hot air
The fan speed dial does not work
The fan speed is always low, unless the switch in the glovebox is flipped, then it goes to high
The blower motor appears to have been serviced before
The other functions of the climate control unit seem to work
Electronic climate controls

What is the problem?

I’m thinking it’s the resister because I can’t adjust the speed, but the hot air makes me think it’s the blend control, could it be both? How can I tell if it is the heater blowing, or if the air conditioning is just blowing hot air? That wiring in the glove box has me confused. Could it really just be the control unit?

 

Let’s start with the call for cooling. When you request air conditioning, does the compressor clutch engage? If so, does the accumulator get cold and sweaty?

George

 

Common failure mechanisms for our HVAC systems consist of vacuum leaks in the engine compartment vacuum hoses that supply the vacuum to the HVAC actuators that direct to where the air flows and a slipping of the gear on its axle inside the electronically controlled blend-door actuator. Less common are failures of the the vacuum control module connected to the HVAC controls. The repairs and parts can depend on they type of HVAC. In my 1999 I have a Computer Climate Control System (I set the temperature) as opposed to a manual one where you set the fan speed, etc.

I would also suggest you check if the airflow through the evaporator is blocked with debris. On my auto-HVAC system, I was able to remove an access panel that allowed me to observe the position of the blend-door. This access panel on mine is where the blower-motor resistors are located on the manual HVAC systems.


Red = access panel
Green = Top of Evaporator



Red= Blend Door
Yellow = axis of blend door axle
(radiator looking thing to right of yellow line is the heater core. The wire mesh wall to the left of the blend-door is the evaporator.

 

Probably going to be best to remove everything that is not factory and then correctly fix it.

Drop the glovebox door down, use your fingers to move the actuators arms to see if anything is stuck.

As Christine stated above, if the vacuum lines have not been replaced, they are likely leaking, so check them and see if you have vacuum going to the HVAC panel.

These are pretty simple HVAC systems....unless an internal door is broken.

 

Alright now I’m just confused, I have the electronic climate control unit, but when I was looking for the resistor I found this:

Resistor?

What the heck is that? It doesn’t appear to have ever been opened, unless they glued it shut or something, but where the plug of the resistor is supposed to be I see only that.

What am I looking at?

 

Here is the rest of what I was talking about earlier:


The switch seems to connect to the ends of the orange wire.

The wires going to the switch in the glove box.

The blower motor.

 

Anyone?

 

That is the access panel where the resistors for a manually controlled HVAC system would be located. That you don't have that means you have the "Computer Climate Control" system. (The one where you set the temperature.) The rubber over-layer covers a metal panel that has three screws that hold it in place under the bumps. If you open it, you can see inside to the blend door. In a pinch if you know your blend-door actuator is bad but you don't have time to fix it, you can open this up and manually move the blend door to full-heat or full-cold (depending on the time of year).

 

Yes. Someone has removed the HVAC blower motor and replaced the rubber over-layer. I'm pretty sure the blower motor has been replaced because I think the brown wire is supposed to be a dedicated ground that was not needed on the replacement motor I installed in my truck. The manual says you are supposed to reseal the over-layer with a rubber compound. I suspect this is to keep dust out. But you can use RTV as long as it doesn't outgas acidic vapors. I think the modern black-RTV would qualify for being ok for this application.

Perhaps they got the wrong part (e.g. wrong part in correct box) or they only had the wrong part available so they rewired it? Or it could be that the control circuit was bad.

The control panels for the auto HVAC control panel in the passenger compartment can go bad (but I think rarely). Maybe that is the problem?

BTW: The electronic module circled in green below is the temperature feedback module. It provides feedback to the HVAC temperature control. There are replacements that can be purchased which would indicate to me that they could fail too. (I don't think that is the right name for them but I've seen them at RockAuto.)

It looks like the previous owner hacked into the wiring for this module. Perhaps that is where the problem is?


I've also attached the schematics for my 1999 Auto Climate Control. Perhaps they will help with the wiring issues.

 

Are you wanting to return the wiring to stock and repair the problem or get the hack to work?

George