Heater Quit

[Bill O']

The heater on my '90 LS400 suddenly stopped working. I've tried every combination of settings on the control panel. I removed the cable from the coolant valve on the firewall and by operating it manually I can get heat in the cabin. I had a friend push the temp rocker switch up and down and the cable that goes into the firewall does not move. Any ideas what I should do next?

[Lexusfreak]

The heater on my '90 LS400 suddenly stopped working.  I've tried every combination of settings on the control panel.  I removed the cable from the coolant valve on the firewall and by operating it manually I can get heat in the cabin.  I had a friend push the temp rocker switch up and down and the cable that goes into the firewall does not move.  Any ideas what I should do next?

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It could be a number of things.....try the easiest stuff first like the thermostat, coolant system change, have the rad & all rad hoses inspected & it could also be your water pump or heater core. B)

[Bill O']

The rad, hoses, coolant and thermostat were recenty replaced. I am able to get heat in the cabin by manually operating the valve on the firewall that sends coolant to the heater core. My guess is that there is some sort of actuator under the dash that connects to the cable that runs through the firewall to open and close the coolant valve. I'm thinking that the actuator has gone bad or there is some problem with the a/c-heater control unit. Does anyone know where the under dash actuator is located and how to troubleshoot? Is there any chance an ECU reset would have any effect on the climate control system? Does the cabin temp sensing circuit go bad? Fuses? -Thanks

[wwest]

Simple.

If you can get a reasonable level of heat by manually operating the hot water valve the the mixing vane servomotor is still operating correctly, and the control cable to the hot water valve has become disconnected from it somehow.

In the alternative the servomotor is stuck in the full warm position but you will soon know if that is the case as the system will not be capable of moderating the heat level.