AC Diagnostics

[Z2TT]

Does your car have hi/low pressure switches, might be something to do with them?

[madmont]

A while back my MX83 aircon would turn on for a few seconds and then turn off . After a short time it would turn on again momentarily. Turned out to be blocked.
If you look down the Tech and Conversions list you will see a recent thread entitled IS200 workshop manual with wiring diagrams. It is a link to a site with Lexus workshop manuals. has a very comprehensive list and on the list if you look hard enough is how to check the diagnostics for air conditioning along with trouble codes. This may be of interest to you
link
http://www.bahamutcars.com/workshop/
amongst other things it says "if compressor lock occurs during a/c operation the a/c switch indicator on the a/c control assembly starts blinking"
hope this helps

[brett_celicacoupe]

i have the ucf11 ac diagnostics stuff.

codes and troubleshooting etc

if you hit me up on msn i can send through the pages

[CrUZida]

Did you look underneath it? Normally they're on the bottom so the wires might have been severed or are tucked up out of view somewhere

Will have another look tonight.
Definitely nothing at the rear, sides or top though.

Does your car have hi/low pressure switches, might be something to do with them?

I couldn't find anything else besides the standard low-pressure cut out switch. Will have another look again though (although on the MX83 and A70/Z20's the dual pressure switch is purely to turn on the fans I think?)

A while back my MX83 aircon would turn on for a few seconds and then turn off . After a short time it would turn on again momentarily. Turned out to be blocked.

Did the AC light flash or would it just stop getting cold?
If I hardwire the clutch directly to the battery she remains cold. I had it running like this for 5 minutes.
Maybe I need to hardwire it and go for a long drive. I don't know how long its been since the system was given a proper run.

If you look down the Tech and Conversions list you will see a recent thread entitled IS200 workshop manual with wiring diagrams. It is a link to a site with Lexus workshop manuals. has a very comprehensive list and on the list if you look hard enough is how to check the diagnostics for air conditioning along with trouble codes. This may be of interest to you
link
http://www.bahamutcars.com/workshop/
amongst other things it says "if compressor lock occurs during a/c operation the a/c switch indicator on the a/c control assembly starts blinking"
hope this helps

Will give it a read, cheers.

i have the ucf11 ac diagnostics stuff.

codes and troubleshooting etc

if you hit me up on msn i can send through the pages

Yeah, if they didn't block msn at work...

[madmont]

Did the AC light flash or would it just stop getting cold?
If I hardwire the clutch directly to the battery she remains cold. I had it running like this for 5 minutes.
(

did not notice the a/c light flashing .

[CrUZida]

If you look down the Tech and Conversions list you will see a recent thread entitled IS200 workshop manual with wiring diagrams. It is a link to a site with Lexus workshop manuals. has a very comprehensive list and on the list if you look hard enough is how to check the diagnostics for air conditioning along with trouble codes. This may be of interest to you
link
http://www.bahamutcars.com/workshop/
amongst other things it says "if compressor lock occurs during a/c operation the a/c switch indicator on the a/c control assembly starts blinking"
hope this helps

Can't find anything there. Lots of pages about the AC diagnostics, can't find that quote of yours.
Can you remember where it was?

[CrUZida]

Just been doing a bit of googling about the subject.
A lot of people have fixed it by changing the cabin filter (which I'm 90% sure I don't have).

Some other people have fixed it by changing the AC Mag Relay liks Z2TT suggested.
Will have a look for it in the engine bay tonight.
Toyota themselves agree.
http://www.toyotapart.com/AC_LIGHT_F...T-EL011-05.pdf


Seems to be quite common on ~2003 cars, but nothing yet for older ones.

[madmont]

Can't find anything there. Lots of pages about the AC diagnostics, can't find that quote of yours.
Can you remember where it was?

I did say you had to look
follow this link from home page
Lexus GS300/GS430 (1997-2005)
click on "Repair Manual" in the column on the left
select "diagnostics" from the drop down list
select "Air Conditioning System" from that drop down list
select "Pre Check" from that drop down list and you will see what I quoted

[CrUZida]

Haha, I had that page up, but missed it coz of how poorly its been converted to PDF.

Everything seems to be pointing to the AC thinking the compressor has locked.

Makes me wonder if the compressor has been changed for a different 1G model at some stage.
Someone has installed a custom speed sensor which looks at the flexplate, so I wonder if this has replaced the speed sensor on the compressor...

[CrUZida]

Had another good look. Definitely no speed sensor on the compressor.

So decided to follow that dodgy sensor thats been installed on the flexplate. Goes all the way back to the compressor, so that must be a replacement sensor when they've installed a non GS130 compressor.

Unplugged the sensor, 110ohms, looks ok.
Started the car up, and 0 volts being produced, so the sensor is either stuffed, or just not doing its job.

Time to hard wire the ACMG input for a while.

[CrUZida]

Dodgy homemade sensor FTMFL

[Dale]

haha they've used an actual speed sensor out of a compressor too... have to give them points for effort

[madmont]

Even if it is dodgy they have been clever and resourceful and found a way to make it work. Most people
would not have the nous to do it

[CrUZida]

I mainly call it dodgy because it doesn't work (at the moment)
Its a fair assumption that when it left the AC shop it was working.

How long it worked for would determine just how dodgy it was.

Will pull it off tonight, hopefully its just hella dirty.

[The Witzl]

10 points for ingenuity, and backyard fixes.

hope you sort it out.