So here's a weird issue I've been having with my 1992 SC300 this spring. I've been thinking the a/c seems a bit weak, as in it works fine except on hot days or when the car has been sitting in the parking lot on a sunny day, ie when the cabin is really hot.

I noticed the air temp coming out of the two passenger side vents is WAY cooler than the air coming out of the driver's side two vents. IE it feels the right temp on the pass side, like warm dog breath on the driver's side until you've been driving around for a good 10-15 minutes. Even then it never gets ice cold on the driver's side.


Once again It seems to usually do this only on hot days or after the car has been sitting in a sunny parking lot all day when the cabin is really hot. Or maybe that's when I notice it.

Any ideas on what could be wrong? I don't think its the compressor, dryer, low on refrigerant, etc. I'm thinking its a problem with the climate control head, a flap in the dash vents, heater control valve, blend door, ie something stuffed up in the dash that's going to be impossible to fix I"m afraid.

I tried to get it in diagnostic mode like the sticky said to read the codes, but I had no luck. For a 1992, do you turn the ignition to on, and push the AUTO **** and recirc button at the same time? That's what the sticky thread said.

 

I think you can rule out the heater control valve. That does its thing upstream from any HVAC routing of the cold air to various vents.

 

Sounds a lot like a blend door problem, just had to fix mine again on my ford 500.

 

Anybody with a shop manual know where the blend door is located? Im hoping its not a whole pull the dash out to fix it job

 

Let's start with the basics first... Our vehicles are equipped with dual climate control, double check that both temp readings are in the "LO" with A/C turned on...

 

Wait, what?

 

Oh crap, just realized I was in the SC 400/300 section...! Lol my bad!

 

LS430s yes.... SCs - no....

 

i have a similar problem. except mine is blowing cold air and out of nowhere hot. not dog breath warm but HOT furnace hot.

i could be experiencing the same problem only mine starts earlier and the all the vents blow hot instead of some.

 

Yours is more likely the heater control valve. A defective valve (or actuator, in my case) would allow hot coolant to circulate which in turn significantly heats the cool air to all the vents as the car warms up.

 

where is this heater control valve so i can go fix this stupid problem.

and thank you for the help. sorry to hijack the post OP

 

This is a very expensive part to replace unless you get a used one from a junk yard. there are no aftermarket versions. New ones can be $500-600 or more. Search the DIY threads as a few members have bypassed this part altogether.

Here is a great link that t2d2 created... There are many others....

https://www.clublexus.com/forums/per...rol-valve.html

 

I have the same issue but i also have a tiny leak. Once i refill to proper pressure then driverside is good!
99 SC400 btw.

 

Okay so I checked all the codes. I got 00, which I believe is no problems.

I also pressed the fresh air button that cycles all the blend doors and motors, etc and it read out 20, 21, 22, 23, 24, 25, 26, 27, then repeated back to 20 and restarted the diagnostic cycle. Is that the normal way its supposed to work?? I think it is.

My next thought is that it might be a bit low on freon. A car I know that has great a/c with a meat thermometer in the dash vent read 50 degrees. Best reading I could get from one of the right vents was 58 or so, left center vent was 70-75, driver's vent was 80.

So its a 1992, did these cars still use R12 back then? I know that was right around the time that they started switching to the newer stuff in cars.

If it is low on freon, what would be the fix, since you can't buy R12 anymore.

 

As far as I know, all the '92s were R12. It should be on a label near the front of the hood, if you want to confirm. You can do a R134a retrofit on most (all?) cars, but everything I've read says it doesn't work all that well. Not sure why.