A/c Fan Speed Issues - 96 Ls400

bermuda1978 · August 17, 2009

I have a 1996 LS400 and the A/C fan speed is acting crazy. The fan can be set to any speed and it will start to go from high speed to low speed at random by itself. It's rather annoying...it acts like it's possesed. I've tried to select "auto" and let it self adjust, but the fan still acts crazy in that mode as well.

Anybody have any thoughts, or seen this before?

Thanks!

steve2006 · August 17, 2009

Hi,

Before doing anything else I would have the AC fault codes read (OBDII) and see if they point you in the right direction.

One thing you could look at is the external temperature sensor used by the AC to regulate the cabin temp ( among others) I have heard the mounting can rust and they fall off ( I think it is behind right side of front bumper)

1990LS400 · August 17, 2009

Bermuda, does your car have or did it ever have a dealer installed Lexus phone? One of the features of the Lexus phone was to lower the blower speed to low during a call and return it to its previously set speed after a call is completed. If it is a phone related problem, unplugging the phone components usually fixes it. If you do have a phone, plug the two large connectors in the trunk together after unplugging them from the phone ECU. If unsure if there was a phone, check under the removable floor on the right side of the trunk.

bermuda1978 · August 17, 2009

Bermuda, does your car have or did it ever have a dealer installed Lexus phone? One of the features of the Lexus phone was to lower the blower speed to low during a call and return it to its previously set speed after a call is completed. If it is a phone related problem, unplugging the phone components usually fixes it. If you do have a phone, plug the two large connectors in the trunk together after unplugging them from the phone ECU. If unsure if there was a phone, check under the removable floor on the right side of the trunk.

Thanks for your reply. I do not have a factory installed phone.

VBdenny · August 17, 2009

so let's say you have it set on low, then it goes on high by itself? do the defrosters work? does the temperature fluctuate?

To me, it almost sounds as if the control unit is experiencing issues but that is pure speculation on my part. Yeah, I agree that checking the codes is the first step.

bermuda1978 · August 17, 2009

so let's say you have it set on low, then it goes on high by itself? do the defrosters work? does the temperature fluctuate?
To me, it almost sounds as if the control unit is experiencing issues but that is pure speculation on my part. Yeah, I agree that checking the codes is the first step.

Everything else functions normally....defrosters....temperature settings...etc. The fan just switches itself from low speed to high speed and back to low speed very erratically on its own. No rhyme or reason.