Defrost comes on when car starts?

[WI93SHO]

Just a day or two ago, I've noticed that when I start the car the defrost comes on automatically, on high.
The EATC is set to OFF, I never use the auto function, and if I turn it on and play with the settings and fan control, I can get the defrost to turn off.

I remember seeing a thread similar to this before, but I can't find it, and I think that one was due to the EATC being set to Auto (mine isn't). And I always turn the EATC off prior to shutting the car down.

Anyone else have this happen?

 

[Mels]

Can't say I remember experiencing that. Curious why you never use the auto mode, I never turn mine off.

 

[Storm-Chaser]

I don't know. Maybe he's trying to exercise his drinking arm


:wave: morning Mel !

 

[SHOZ123]

I hate the auto button and never use it.......

 

[Mels]

'Mornin, fellas!

 

[Storm-Chaser]

What you're describing is a common failure of the Blower Control Module. A few have described this specific symptom as a result of the Automatic Temperature Control Sensor (resistor behind the "SHO" emblem on the dash) getting clogged with dirt and debries - and have corrected the problem by cleaning the resistor. This is mentioned in one or two of the very early posts.


It module is referred to as the A/C Blower Motor Speed Control, which you will find referred to here as the Blower Control Module, Blower Speed Control, BCM, or BSC.

You'll find the most information using "BCM" as a search term, which returns 103 prior threads. If you have time, read through them. You'll learn how to diagnose this problem, as well as a handful of other Blower Control Module, Blower Motor Resistor, Blend Door Actuator (BDA), and Electronic Automatic Temperature Control (EATC) problems. There's at least a half-dozen threads you'll probably end-up bookmarking for future reference.

It's a relatively easy repair, and the part can be found in the junkyard for $10-to-$20, as it's $244.98 Dealer List.

Just a day or two ago, I've noticed that when I start the car the defrost comes on automatically, on high.
The EATC is set to OFF, I never use the auto function, and if I turn it on and play with the settings and fan control, I can get the defrost to turn off.

I remember seeing a thread similar to this before, but I can't find it, and I think that one was due to the EATC being set to Auto (mine isn't). And I always turn the EATC off prior to shutting the car down.

Anyone else have this happen?

 

[Dinosauro]

Take a look at TSB # 94198 - Sep 94. Might be relevant.

Dinosauro
2/4/08

 

[WI93SHO]

Thanks for the help guys, it actually hasn't done it lately, I wonder if the really cold weather had something to do with it?

I will be cleaning out that sensor for sure though.

 

[Storm-Chaser]

If you will read through the prior posts, several talk about the intermittent nature of this failure, which is due to corrosion of the PCB (circuit traces) and/or electronics (relay/resistors) on the circuit board.

When you pull the module, the entire bottom-side of the PCB and the internal electronics hidden under the cover should be covered with a red-colored protective epoxy sealer. If the failure is due to corrosion, you will likely notice discloration of the bottom-side of the PCB.

Essentially, water from condensation, clogging drain tube, or vehicle leak is what causes the corrosion. And every time that cause reoccurs, additional temporary circuit chorts will occur until it completely fails. There is a minor risk that it will start an in-vehicle fire according to one post.