MrUnicorn

I have a 1990 LS400. Had to work on AC. Upgraded to R134. System had not worked in 4 years. Had to replace line and recharge system. All went OK. Gets very cold. Shut off car. Went to try again. AC light blinking,compressor not coming on. Can not see codes when I check because face is black, from heat. I think it is the pressure switch, but do not know how to test. Do not have manual. Do not know how to jump switch to make compressor come on. Has 4 wires. Can not find on net. When I let car set and cool down. AC starts and works till I turn it off. How can I test? Help..

dicer

Was the system vacuumed before recharging it? "AC starts and works till I turn it off." Till you turn off the ac or the engine?

MrUnicorn

Yes on vac. Both, when you turn off AC. or if you turn off car. AC works in early morning, till you shut down. Then in may take hours to come back on

dicer

It would be nice to fix that lcd, could make figuring the problem out easier.
I looked at a 92 electrical diagram book, 90's are pretty much the same. It shows the AC pressure switch with 2 wires one is a Yellow - Black it goes to the PSW terminal on the AC control unit, and grounds that circuit. The other wire from the switch goes to ground it is White - Black. Meaning white wire with black stripe.
So if the 2 wires are jumpered that should do it. But to be careful I would use a test light to ground the Yellow - Blue wire.
There is also a High pressure switch that is for the cooling fan relay.
There is also a magnetic clutch relay that is operated by the engine transmission ecu. And it looks like the ecu is the ground for that relay.

dicer

Could also be the compressor lock up system, that counts pulses from ignitor and the compressor and compares them maybe a slipping belt could cause that, but I don't see the cold vs hot deal there its suppose to blink the light and shut down the compressor if there is an error. Then there is the EPR evaporator pressure regulator that keeps low pressure over 27 psi to prevent evaporator icing.
The diagram in the shop manual looked a bit different from the electrical diagrams book for the pressure switch, but still mentions checking for continuity of the switch.
Have the ac system pressures been checked? Did you do the service or have it done?

AaronUCF11

Kinda sounds like it could be over charged and high pressure switch cutting it. If you have a gauge set, this will tell you a lot about whats going on in the system.

rcftx68

Hi all,
I have a 93 SC 400 and my A/C which had an evaporator core leak was replaced with a new core. The A/C has been working great since, however I noticed recently on occasion my A/C button light would start blinking and the compressor would not kick in. If I turned the system off and back on a few times the light and system stays on with cold A/C. This trouble has been getting progressively more frequent and I am wondering if it may be a wiring problem or that my compressor may be going out. Obviously when the A/C switch is blinking the compressor is not working and there is no cold air. So where do I begin to try to diagnose the problem?

dicer

How much did they charge to replace the evaporator? Or did you do it? That is like a total interior overhaul doing that job, and looks like way more involved than R an Ring the engine and transmission. But then an SC which I didn't notice the first time maybe different from an LS400.