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ripster
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Hi, I'm new to the forum so I'll try to get this right. I have a 2000 LS 400 and lost cabin heat. Wouldn't matter if I set the temps to 85 or 65 = no heat.

I bought a thermostat and heater control valve. I installed the thermostat and no change.

I was looking at the heater control valve just behind the engine towards on the fire wall just a little off center towards the driver side and noticed that whether I turned on the AC or Heat or whether it was at 65/COLD or 85/HOT that the heater control valve wouldn't move.

I moved it, with very little resistance and left it in the full "up" position and then turned the heat up to 85 and I had heat. I turned the temp down to 65 and put on the AC and I had cold air. With each change I would look at the heater control valve arm and it had not moved. Once again I tried to move it "down" to the "shut" position and it moved easily and I was back to no longer having any heat.

I've tried finding some details as to what moves the cable that controls the heater control arm and it appears that it is the servo motor.

Is that my next step or am I missing something. Any suggestions and/or questions would be greatly appreciated. Thank you.

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Yes the heater control valve is operated by a servo motor via the cable, there are several servos operating air flow and direction also.

It will be a case of getting under the dash and trying to locate the cable from the valve and where it attaches to but this will probably be well buried.

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Yes the heater control valve is operated by a servo motor via the cable, there are several servos operating air flow and direction also.

It will be a case of getting under the dash and trying to locate the cable from the valve and where it attaches to but this will probably be well buried.

Does it do any harm to any of the components just to leave the heater control valve in the upright (opened) position during the winter and then I could work on it in the spring? Thank you for the reply.

And yes it would appear that Ill have to take apart some of the dash to get to it.

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Just my opinion that it will do no harm to manual set the valve so that you have heat for the Winter. Then, in the Spring, determine and fix the actuator that moves the valve.

I'm pretty sure it won't hurt, I found the "Water Valve Control Servomotor, behind the lower portion of the center stack (containing the screen and climate/audio/nav controls). It's on the drivers side near the evaporator.

There are four servomotors there, one for the Air Outlet, one for the Air Mix, one for the Control and the Water Valve with the cable attached. Thanks for the input, it looks like it's the culprit.

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I'm breaking a 1997 LS400 and the servos are probably the same, I would be quite happy to remove it for you and post it over for the cost of the postage only if that would help.

It might be a little early for that, I need to get to the servomotor, see if it's getting electrical before I know if it's the issue or if it might be the control unit. hate to keep buying parts until I figure out which one I need.

When I get to do this, I'll get back to you and see if the part numbers match. Lexus told me that 1998-2000 has identical parts throughout while 1990 - 2000 will have many identical parts but also many that are not the same and I should check. Thank you for the offer, if it looks like I need the water valve servomotor, I'll check and see if you still have it.

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  • 4 weeks later...

I've tried finding some details as to what moves the cable that controls the heater control arm and it appears that it is the servo motor.

I have a circuit diagram but it's for a JDM and the many characters there are not alphabet. You can see wiring connections but it a bit hard for you to understand fully. I just put a red and a blue circle to indicate those two key components in English.

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