divineVIP

As of the2 weeks ago im a proud lexus owner. A beautiful 1990 ls400. Although with high miles. She is in near mint condition, but just yesterday i pushed the a.c. and i got no response. Its not the a.c itself, just no electricity going to the any of the a.c buttons. I checked fuse no. 15 under the driver sidekick panel, but it was fine. I was also told it could be the relay, fusable link or circuit breaker. Are there other fuses or relays for the a.c i should check? If so where are they and how doin determine if it needs replacing? Anyone who knows about this PLEASE HELP i live in Vegas where i have to deal with 100+ degree weather.

LScowboyLS

does the fan work?

is the front defog light flashing 10 times?

does the A/C button light up when you push it?

no compressor engagement can be many things, the most likely would be:

fuse or relay
low pressure sensor
high pressure sensor
failing ECU capacitors
compressor clutch
electric fan switch
compressor clutch coil

divineVIP

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Yea, the fan starts right up. But no lights come on at all. The entire dash interface with the ventilation options(buttons) has no electricity going to it. All my other electronic options function though.

johnnyg66

You didn't check it before you bought the car? Too bad. So you think it may be the unit itself? Try and find another used one to swap out and see. So the fans come on but its not cool? Make sure the ac clutch is engaging too.

divineVIP

No no. You both misunderstood me. I tried to clarify this earlier. My a.c. and heater was running fine with no problems until yesterday, now there is no electronic function to the buttons on the dash to activate any of the ventilation options. The clock still works though.

divineVIP

I'm pretty sure there's nothing wrong with the compressor or unit itself, just an electric problem. That already for sure. But i dont know which fuses or relays to check..

LScowboyLS

check the following fuses:

FR CIG
HTR
FUEL OPN


relays:

Heater
A/C

divineVIP

Is there anyway you could provide a diagram of where the relays are? I know they'r in the engine compartment, but which ones are they. Same for the fuses. Thanks for helping

Twista4004

I've got a similar issue of no AC

I looked at the kick panel on my 93 LS and have nothing in that slot. It says RR AC 15 but doesn't have a fuse. Doesn't even have the contacts that would hold the fuse in place when I tried to stick a fuse in there to check. I even went to the U-Pull-It here and found 3 1LSs all of which had every other fuse but none in that RR AC location. --wondering if that was only for specific trim cars to have that fuse. I dunno



All in all, I'm convinced that failing ecu capacitors are most likely the culprit -- for both my and your issue.

divineVIP

just fixed my a/c problem! I went back underneath sidekick panel and literally checked each and every fuse. I came across only 1 burnt out fuse. It was the radio fuse at 17.5 amps. It brought electricity to the air conditioner as well.

LScowboyLS

yay!

- glad you finally checked all the fuses!

but ya still better be getting ready for those ECU capacitors!

(especially y'all in the 93-97 range on LS400 and even earlier years are commonly affected on SC300, SC400, etc.)

divineVIP

BAD NEWS!!!
After i put in the new fuse, and turned on the a.c. it didn't blow cold air! I drove to autozone and bought a $40 can of r134a to recharge it, and it was a bust the meter read that the pressure in was really high. Then i WENT to check the compressor and noticed it wasn't spinning. The guy at autozone said it's it's the entire compressor that will need replacing or just a restriction somewhere in the lines which is an easy fix. He also told me he works at an autoshop where he can give me an a.c diagnostics test for $50.

LScowboyLS

QUIT listening to guys at autozone - if they knew anything about A/C, they would be making 80K+ as a dealership A/C technician, not 18K at autozone

a restriction in the line is NOT an easy fix, as the restriction would be at the narrowest point of the system, the expansion valve, which is a bear to get to under the dash - and further, a restriction means there are other issues, and at a minimum requires a system flush with a flush gun (big $$$)

you nor he have any evidence of a bad compressor, which cannot even be determined without a SET of gauges (and some knowledge), not the single gauge on the can

LScowboyLS

when the compressor is not running, the pressure on either side of the system (high side or low side) will be over 100 PSI, as it should be!

here is something else that makes the autozone guy's ideas seem silly, I recently had the same symptoms as you, high pressure on the low side (due to compressor not turning), and just blowing hot air, now I could have replaced every single piece of the A/C system at over $5000, and guess what, it still would have been blowing warm air, because in this case the problem was failing ECU capacitors! - once I fixed the capacitors, the system is now icy cold, never even touched any A/C components or even a can of refrigerant!

Gene01

I believe that "RR AC" refers to the rear Air Conditioning system.
This is true for the LS430 (UL), but I can't say for sure on the LS400.