Hi all,

i have a 1990 Lexus LS400. my problem is that my A/C system is not automated. when i turn on the A/C it work and automatically shuts off from the thermostat and after few sec. and kick back on but this at point my A/C light blinks and the clutch not engaging (No A/C only the blower works) so i always manually off the A/C and on again.

A/C system is not automated like another system.

I really don't know how to explain but i did my best to explain it to you all so please help me fix this issue.



Thank you

 

First thing I would check is the system pressure. Either low or high. If the compressor is cycling on/off that quickly, you may have a low pressure situation in the system not allowing the compressor to run, as there is not enough refrigerant in the system (this means you have a leak somewhere).
The other possibility, is the system being over pressurized. As a safety, the compressor will not run, if the system pressure is too high - could cause some real damage.

Have you had the AC system serviced recently?

 

There is an easy diagnostic test you can do with the HVAC systems on these early cars (at least). I forget details, but it is something like: hold in two buttons on the HVAC control panel when you turn the key to ON. I don't remember which buttons, but you should be able to search and find that here. It then runs through an automatic test, returning specific HVAC error codes that you can then look up. I know this works on my '91, and it should too on your '90.

Our early cars took R12 (mine still does), vs. R134a, so watch out for conflicting advice on that. I think the switch was made around '94.

There is a sight glass to the right of the radiator - you'll probably need to clean it off first, but watching that might give some clues.

Of course getting pressure measurements will be good to do, but these are some things that might help if you don't have any tools.

 

http://www.lexls.com/tutorials/air/accodes.html

This is how to check for the codes and what they mean. Not sure how to check for pressure on the 90 but on my 94 (with R134a) I just bought the refill can with the gauge on it, I dont think you can do that with the R12. On my 93 (which is when they switched to R134a) after I drained the system, to change the heater core, my compressor would go on and then off quickly like yours probably b/c of no pressure. I never refilled that one so it never worked again.