Still Trying, But Still No Heat

[pfleyva]

I'm hoping someone can help me with my next step.

I have a 94 Ls400. There is no heat unless I turn off the a/c choose a lower vent, turn system to Max Hot and wait about 15 minutes. I then get a trickle of warm air.

All of the a/c codes are fine. When I manually move the heater control valve either completely open or closed the system stays cold.

I can manually move the cable about an inch in and then out, I even lubricated the cable.

When I have someone change the temp from cold to hot or hot to cold, the cable does not move at all. This is with the a/c on or off.

Any suggestions? Thanks, in advance.

[RFeldes]

The Lexus will "not" turn on the heat until the engine is warm. Same with my 90 as my 02. They decided no cold air blowing until the engine is warm and able to blow warm air. Makes sense to me. Are you saying it won't blow warm air when the engine is at or near normal temp? The cabin temp sensor is on the dash and is about 1/2 inch in diameter with three or four slits. Make sure it is not clogged.

[SKperformance]

follow the actuator cable back up to the motor.

Open the ducts and doors to look for obstructions.

[pfleyva]

Thanks for your comments:

Yes the heat NEVER comes on. I've already cleaned the sensor.

I'll follow your advice SK. Hopefully I'll find something

[TexasLexus94]

My 94LS had a similar problem recently. I think, due to my poor maintenance, that the coolant level got low. This resulted in no heat in the cabin. I noticed that the engine itself would not overheat, but pushing the "auto" heat/cool button only turned on the A/C, but did not produce any heat, or even turn on a fan. On manual position, the fans ran, but still no heat. As a result, I filled the system up with anti-freeze, and also replaced the thermostat at the same time, since its an easy and cheap change out. I'm not really sure if the problem was the coolant level or the thermostat, but the system is running great. Just my thoughts. Best of luck.

[wwest]

If the cable connected to the water control valve doesn't move at all when its disconnected from the valve and the system is commanded from max cold to max heat then the blend door servomotor inside the A/C plenum under the dash center is stuck or has failed.

If you are sure, CERTAIN, of the above then you might be able to force the blend door into the max heat position via the appropreate pressure on the cable core and then (***) tie the water control valve open. Then use the blower to regulate the cabin heating level.

***After checking to make sure your "pressure" didn't unstick the servomotor.

[pfleyva]

Thanks wwest, I'll give it a try. Is it difficult to replace the sevomotor?

[wwest]

Haven't tried it but according to the Lexus shop manual it's a Bit***ch.

[pfleyva]

Well, I guess I'll try yanking on the cable to free it up. If that doesn't work I'll try a warm coat.

Thanks for you help.

[kenaty]

I'm hoping someone can help me with my next step.

I have a 94 Ls400. There is no heat unless I turn off the a/c choose a lower vent, turn system to Max Hot and wait about 15 minutes. I then get a trickle of warm air.

i got similar problem with my heater.

mine seens the fan not working, i can feel theres still small warm air comming out of the vent after the engine in normal temp. manully control fan to HI doesn't help.

however, i drove to around 1 and half hr and fan works again. don't know what is the problem.

[SKperformance]

You may have something sticky like tree sap tieing up the motor.

[BogeyJH]

I had the same cable issue, with the exception that the heater control valve (HCV) was leaking. [see my McGoo pics here.]

Last night, I replaced the leaking HCV. I was so sure that the new HCV would solve the no heat issue, but it didn't. Oh well, it leaked and needed to be replaced anyway.

BTW, either I'm missing something or the clamp on the hose that connects to the bottom of the HCV is not serviceable. I've never seen this type of clamp. It included a cotter pin which I could not remove. I ended up cutting it off and put a new

worm gear band clamp

in its place.

Now I need to address the cable, which doesn't move. It was pretty stiff and I lubed it and was able to move the cable in and out, but it doesn't move easliy. The blend damper is functional. With the AC on and the control in "AUTO" mode, I can hear it move and the air flow changes from frosty to only cool. At full HOT, the air from the vent is outside air temperature.

Is the HCV controlled by the same servo as the blend damper or is it a separate motor?

[BogeyJH]

Is there anyone out there who knows if the heater control valve is actuated by the same servo as the blend damper or is it a separate motor?