rcollins1

This winter, the passenger side won't blow hot air while the driver's side is fine. I've cycled both sides to Lo and Hi in various combinations but that didn't work. I thought there might be 2 separate heater cores but then one posting talked about "Servos" but was unclear on what they did, where they were, and if that fixed their low coolant (duh!) problem. I in fact have not checked coolant level but again, drivers said does blow hot air. Coolant temp gauge is rock steady at about 1/2 way. New timing belt and therefore new water pump was recently installed (205kkm) but I don't see how that could affect one side of the dual zone climate control and not the other. Any good technical assistance would be much appreciated before I start doling out cash to my independent garage or heaven forbid the dealership!

BlackCat81

A very common symptom of a large air pocket in cars with dual zone climate controls is hot on one side, cold on the other. If it were me, I'd make sure I really bleed the cooling system. A Servo is an electronic device, that in this instance, is used to power a blend door. A blend door is basically a trap door inside your HVAC box that opens and closes to allow the system to reach the desired air temp. So if you have a bad blend door motor, for example, a fresh air duct might be staying open, not allowing the system to blow hot air. Make sense?

rcollins1

Thanks BackCat. Yes, it does make sense. That's even what my wife suggested! Is clearing the air pocket as simple as bringing the engine up to temperature with the radiator cap off (if I can even find and get at the rad cap) or does it require circulating the fluid under pressure and better left to a properly trained and equipped mechanic? I used to be a fairly competent shade tree mechanic but on cars built in the 60's and 70's. If it is not an air bubble it sounds like it could still be a servo that has died. Correct? Thanks again for you astute help BlackCat.

BlackCat81

Since you said you recently had the cooling system open, my vote is air pocket. However, these trucks are also known for bad blend door motors as well, so could be either one. Ya, I use a spill-less funnel for burping cooling systems, it keeps the mess down. With the funnel screwed into the radiator, let the truck warm up and then cycle between revving the engine and letting it idle. If it's still being stubborn, lifting the front end on jack stands to let gravity help you can work too.

rcollins1

Thanks I'll try that when I get home to the city, my garage, my tools, and an auto store. Yesterday, I did open it up and rev it to 2krpm for a few minutes while cycling the temp controls but that didn't work. There was a very small amount of spillage so I confirmed rad was full and I was circulating at 2krpm.

chiph9

Park it on a hill with the nose higher than the rear (10 degrees or more) and let it sit overnight. If there is a bubble, it should go to the highest part of the system, which will be the radiator at that point.

Chip H.

rcollins1

I did lift the front end on 8-10" ramps and went through the heat up and rev process with no success. I found that the passenger side was blowing warmish air when turned from Lo (freezing air) to 18 deg C (first setting above Lo) and the air did get slightly warmer when I instantaneously went from 18 deg C to Hi. Could it be a partially stripped gear on the blend door servo motor?

chiph9

Yeah, blend door mechanism would be the next thing to look at.

I seem to recall that there are A/C system diagnostics available via the touch-screen, if you have the Nav option... Try looking for those & run through them.

Chip H.

mswtoyota

Interesting stuff here:
https://www.clublexus.com/forums/gs-...rvomotors.html

rcollins1

Hey Chiph9, would you recommended warming up and then letting sit and cool overnight with rad cap on or off?

chiph9

If the coolant is hot when you shut it off, the overflow valve at the radiator filler neck will be open so any air that ends up there will go out the hose to the tank. So it won't matter if the cap is on or off.

Chip H.

rcollins1

Will overflow valve still be open when rad has gone from hot to cold? If I remember the set up, probably not. Best just to leave the rad cap off while it cools? Per BlackCat's post, I have a funnel set up so there is no spillage.

chiph9

The overflow valve will be open for a while, until things cool off. By that time, any air will have found it's way there and out the neck.

But it won't hurt to leave the radiator cap off. Just be very careful when removing it while the engine is hot - it will likely come steaming out.

Chip H.

rcollins1

Left the rad cap off and let it sit overnight (on 8-10" ramps) to cool. No luck. The DIY posts look doable. If I was 25 yrs younger and had the physique and patience and no wife not wanting her car down for days and days and days. I guess the Lexus Dealer is going to get a pound of flesh out of me. Hopefully not an arm and a leg too!

rcollins1

Nav system does not have any diagnostics in it. Off to the dealer for a $139 hour of diag.