I’m looking for the low side pressure switch on a 99 Lexus es300. I’m following the larger refrigerant line from the compressor and it looks like it runs through the firewall to bring the dash. Before I start tearing things apart, can anyone confirm the location of this switch?

 

There is a pressure switch right by the receiver/drier (might be right on it can't remember) it is both a low and high pressure sensing switch. What problem are you trying to diagnose?

 

Thanks, I’m trying to diagnose an a/c issue. Compressor doesn’t engage. System is full and has been vacuum checked. Magnetic clutch relay and climate control has been replaced. I can only get it to blow cold air when pins 3 & 5 on the mgt clutch relay are jumped. Tried driving it for about 2 mi then the ac light started flashing so I pulled over and removed it. The vacuum switch near the accumulator (hi pressure line) has been checked for continuity and checks out. Solar sensor works as there are no trouble codes diagnosed by the on-board diagnostics comp. I’m out of ideas at this point as to what the issue could be; especially now that there’s only one pressure switch and not two??

It does read hi and low megapascals which makes what you’ve said make sense.

 

There is only one switch AFAIK, there used to be two in the past (high and low). As I've stated in the past I don't know much about A/C systems we have a couple of members here that know much more and will chime in.

 

Hello,

How did the issue first begin?

Check the Continuity of Pins 1 and 4 on the Pressure Switch, while they rarely fail, it may be a possibility.

Sounds a lot like an issue described here, which turned out being the Lock Sensor on the Compressor, it is designed to tell the ECU if the compressor is spinning, and shut down the system if it locks to prevent further damage to the AC system or the drive belt, it also never showed any error codes in the Diagnostics menu. You can probably check it with a multimeter, but to actually see the signal it puts out, you will need an oscilloscope linked in the thread.

Hope this helps and best of luck!

 

Thanks for reaching out. I’ve read the thread and it is very detailed. Pins 1 & 4 on the pressure switch also shows continuity and the fan actually cuts on when I unplug it so that’s good. I think my next move will be to replace this speed sensor. I’m pulling this one off a Delphi brand compressor that was formerly on a 04 Avalon to put on this Denso compressor. I’m assuming that I’ll need to have my system evacuated. I don’t recall when exactly that the compressor stopped working as it may have been winter at the time but when it came time to use the ac again it just never worked. In the meantime while I work on this sensor, is there any other sensor that I haven’t mentioned yet that deals with the system?

 

Yes, it will require evacuating the system to replace the sensor, and I have my concerns about Delphi sensor working too nicely with your Denso compressor. Before you do that, I would suggest diagnosing the existing sensor instead of throwing parts on problems, it may not end up being the sensor at fault, which could be quite unfortunate considering the amount of work required to replace it.

Hope this helps and best of luck!

 

A/c doesn’t work and only blows cold if I jump the magnetic clutch relay. Clutch won’t engage when a/c button is pressed. Car has never been in an accident. It just stopped all of a sudden. Can someone point me in another direction? I’m out of ideas at this point.

To date, I’ve verified:

Changed out a compressor with a new one.
Changed out climate control unit with one used.
Solar sensor is functioning (no codes on climate control unit).
Pressure switch works (fans engage once disconnected).
System vacuumed and leak tested.
New Denso magnetic clutch relay (old and new relay audibly clicks).
All fuses checked.
No broken wires (clutch engages when jumped at relay).