1990 Lexus ls400

[Cody alberger]

I have a 1990 Lexus ls400 and barely any air is coming from the vents. The heater core lines are capped off from previous owner. The blower motor strength is good and I also cleaned out the evap core. Still barely any air. The ac/heat controls light up but if I change it to low medium or high air it doesn’t change the fan speed but it must be stuck on high because it spins fast and it’s loud. Ik the blower is moving lots of air and the core is cleared I’m not sure what could be the cause of the lack of air power out of the vents.

[Lexus Owners Club]

Hi Cody......welcome to the Club

I would advise to check the Cabin (Pollen) Filter as if this blocked then no air will come through.

Cheap and easy to replace but may have to crawl under the dash to access it

[1990LS400]

3 hours ago, Lexus Owners Club said:

Hi Cody......welcome to the Club

I would advise to check the Cabin (Pollen) Filter as if this blocked then no air will come through.

Cheap and easy to replace but may have to crawl under the dash to access it

 

You can check for a filter but don't be surprised if you don't find one.  The 1990 LS400 I drove from new to 14 years didn't have one.  The first model year that a filter is shown in the parts list is 1992 but I thought that 1993 was the first model year that the North American market gone one.  The Lexus organization made quite a big deal when the HEPA filtration system became standard on the LS400 in the North American market.  It was an expensive option on the Japanese market Celsior (LS400) in the early years.

Ducts in the HVAC system could be clogged with who-knows-what or electric servo motors that open and close flaps in ducts might have failed or the flaps could be stuck.  It sounds like the HVAC system is in sad shape if a previous owner capped the heater core and the fan is stuck on high.  Debugging the fan speed is further complicated by it being also controlled by the phone system.  Even if no phone was installed, corrosion of the factory phone system prewiring can cause all sorts of weird problems including putting the audio system in permanent mute. 

[Bykfixer]

Woah, woah back up a few ticks. 

The fan is also controlled by the phone system? You mean telephone, right? As in cellular? As in those big ole bag phones? Or walkie talkie type? In 1990? 

[1990LS400]

56 minutes ago, Bykfixer said:

Woah, woah back up a few ticks. 

The fan is also controlled by the phone system? You mean telephone, right? As in cellular? As in those big ole bag phones? Or walkie talkie type? In 1990? 

The Lexus brand cell phone that was a dealer installed option lowered the HVAC fan speed and muted the audio system while a call was in progress.

I even connected an aftermarket Nokia CARK-91 phone system I installed in my second (2000) LS400 to mute the audio system but I didn't bother to connect it to lower the HVAC fan speed.  

Even when a Lexus phone system was never installed, corrosion of the factory installed cell phone harness in the trunk can cause HVAC and audio system issues.

[Lexus Owners Club]

2 hours ago, 1990LS400 said:

The Lexus brand cell phone that was a dealer installed option lowered the HVAC fan speed and muted the audio system while a call was in progress.

I did not know that....makes sense though!

[Bykfixer]

Impressive!! 

That sounds pretty standard these days but that must've raised a few eyebrows back then when a premium car stereo would turn up the volume based on road noise, but to lower the fan speed of the comfort system when the phone rings?  Heck, I think in my modern day appliances called automobiles they still don't do that. 

 

[1990LS400]

30 minutes ago, Bykfixer said:

Impressive!! 

That sounds pretty standard these days but that must've raised a few eyebrows back then when a premium car stereo would turn up the volume based on road noise, but to lower the fan speed of the comfort system when the phone rings?  Heck, I think in my modern day appliances called automobiles they still don't do that. 

 

I suspect that the reason that the reason that Bluetooth phone systems standard in newer vehicles do not turn down HVAC fan speeds is that noise cancelling microphone technology makes it unnecessary.

Automatic radio volume increase based on road noise has been around a long time.  The volume of radios available in the 1957 Ford Thunderbird increased with speed and the radios also a search feature that would find the next available radio station on the dial.

The 1956 Mercedes 190SL 2-seat convertible I drove as a kid even had a turn signal like lever on the steering column that would cause its Becker Mexico radio to find the next station.  Mercedes sedans of that era and into the 1960's had optional foot operated switches that would cause the radio to search for the next radio station - pretty sure I have one of those foot operated controls in a box in my garage.  These crude radio remote controls could even be attached in series so that each passenger had their own.