Hi guys,
This is my first post ever, so hello! I've been stalking the CL forums for a while now, but this'll be my time interacting with the forums.
Regarding this issue, here's some context. I recently bought a 1998 Lexus GS400, and all was fine and dandy. AC however recently stopped blowing for me. I will leave it alone and cruise with the windows down for weeks at a time and sometimes whenever I turn on the AC, it would either 1. Work and blow ac for ~4/5 minutes and then slowly dwindle to nothing or 2. Not work at all, only feel the slight breeze from the outside air coming into the cabin. Here's some repairs I've done in hopes of fixing the problem to no avail as of date.
I've repaired the AC Blower Motor, AC Blower Motor Resistor and I've done visual inspections to the servos for the Mode and Wind Door (Or whatever it's called, the door controlling cabin and fresh air circulation) and they're in working condition.
Here are some symptoms :
- When I press turn the AC on, I can hear the electrical withdrawal to the car that all is engaging as it should but no air. ie : When I start the car, it will idle higher when AC is engaged vs not.
- When I do feel the slight breeze from the outside air, the air is ice cold which should mean the AC compressor should be fine (?).
- Front and Rear defrost work fine, but take time for it to defrost ice or foggy windshields.
Any ideas on what the culprit could be? I have no multimeter as of yet so I can't do a full diag of the electricals, but I'm hoping someone else has had a similar problem they've fixed. I can only think of the AC relay/fuse that could be the culprit.
Anything helps, thanks y'all!

 

Air conditioning systems can be tough to teach via a forum. You really need to find someone who can be there to do the work with you on the vehicle. If that’s not an option and you really want to learn how an automotive hvac system works and how to diagnose it and repair common issues for your car then I would recommend finding some YouTube videos that explain the basics and the components, Then you’ll be able to decide if you still want to invest your time and the money in the necessary tools to be able to diagnose and repair your vehicles problem. You’ll need a good set of gauges at a minimum, u can buy them or some parts stores will have them in their loaner tools. Then if you can find out some a specific problem and would like some help with how to repair it, then you will have much better luck getting help here. Example, if you find out your system is completely empty of refrigerant and then put an evacuation pump on and your able to isolate where the leak is, and want some advice on where to get quality replacement components and how to replace it, you’ll find these forums to be much more useful in the future.

 

I'm following all new AC related threads since I'm dealing with similar issues. I would definitely check the AC compressor relay and test for good continuity. I been reading and checking YouTube myself regarding the relay's. Even if they click then ground and power is added, the relay can still be off.....a multimeter is great to have.

 

Could be the controller. Try msnual settings see if it responds. I suspect you only tried it in auto.
It has Itself diag mode also using the buttons on the controller. Ck this forum for that.
Temp sensor can be eliminated with diag checks.
You can run a diag on it with a good obd2 scan tool
search SC forum

A/C system diagnostics- Need codes.

 

The relay and controller and all the electrical components can usually be quickly ruled out, or in by simply using a jumper wire and running 12 v directly to the compressor wire harness. If u have access to a wiring diagram for the AC, then u could quickly identify which pin in the plug needs to be powered up. An alternative method would be to just take a standard test light to the plug and then check and see if money of the pins has power switching on and off with the dash switch. If your not getting any power at the plug, then you can chase down relays or blown fuse or bad controller etc. i believe the plug only has a couple wires running to it. I will take a look at the harness in my gs400 if I get a chance today. And see if I can map it out, and then I will post it for you.