lutz7680

I just bought a 1991 ls400. When I push the ac button or the defrost button it shuts the car off. Any Idea? Car has 157000.

deanshark

It needs either a new battery or an alternator. One of those doesn't have enough juice. When you hit the defrost the A/C automatically turns on and it just draws to much power to keep the car running. Does it start back up after it dies? How does it run if you don't use the A/C? Have you noticed lately if your headlights dim when you hit the brakes? That's the start of a bad alternator.

cf3232

Turning on the AC creates a bigger load on the engine. There is a circuit that makes the car idle higher to handle the AC added load. It does not seem that way because the engine still idles down to a normal level, but in all actuality the engine is idling higher. There is probably something preventing the circuit from working properly and making the engine idle higher. You may want to get a electric diagram and find out how the circuit works and how to go about troubleshooting it.

It may be something else, but this sounds like your problem.

yahoo_san

I had a similar problem or maybe even the same problem. What happened to my 92 LS was my A/C compressor froze. If my RPM's were low when I turned on my A/C, my frozen compressor would stop my belt completely and would kill my car. If I was driving and my RPM's were higher when I turned on my A/C, the car would shudder and the RPM's would drop for an instant but the car wouldn't die out. The A/C wouldn't work and the light would just blink.

I was pretty pissed because this problem came up 30 minutes after I bought the car and I already had to change the A/C compressor, which I didn't because I didn't have the time or money. I eventually just sold the car about a month later...

I really hope you dont have the same problem though, just wanted to give you a heads up of what happened to me.

LEXTEK1

I agree its the compressor. Reach under the hood and see if the compressor is locked. You can turn the front plate on the nose if its free..

Supralaju

either ground or AC compressor relay

cf3232

Did not think of this, very good point. Make sure the compressor is free.

DjBlitz111

This isn't the correct forum but I have a 1993 Lexus GS 300 and the same thing happens. When I turn on the a/c the car shuts off. I already replaced the alternator and I don't know what the problem is. PLEASE HELP!!!!!

Banshee365

Remove the belt, start the car, and turn the AC on. See what happens.

DjBlitz111

Which belt?

oldskewel

iTrader: (1)

I assume he means the AC compressor belt, which on these cars (I'm pretty sure) are the same as the altenator, fan, etc. belt. I.e., there is only one belt you can see (the timing belt is hidden behind covers). That is the one to remove.

I will agree, that that is a good way to start the debugging process. See if the car still dies with the belt off. Also, you may be able to test more easily for a frozen AC compressor with the belt off.

dicer

Wrong forum

Losiracer2

I had a problem with an old DD 92 Honda Accord where it would do something similar, the whole engine would shudder anytime I pressed the A/C button.

It turned out to be a clogged expansion valve on the evaporator not allowing the A/C refrigerant to pass through the coils like it should. So, I would suggest this if your compressor clutch is free to turn with the engine off. Chances are you have a blockage somewhere in the system which in turn will affect the operability of the compressor.

djamps

+1 on the compressor. Defrost uses the A/C as well so both functions would have the same result.

bible44840

Lexus tech said the a/c amplifier is causing the car to shut down. There is a replacement part to address this issue.