01 Ls430: Aircon Expertise Needed, Some Diagnostics Already Done

[Suprazed]

Hello all, I just purchased a 2001 LS430 a couple of weeks ago, the car has 175k on the clock but runs beautifully.

However, the air con does not function, to be precise, the magnetic clutch does not engage when the a/c is switched on. I had it re-gassed but this did not help and the a/c still doesn't engage, the guy did say that it seemed to be holding pressure fine though, he evacuated about 150g and then refilled with about 850g in total.

I've so far performed the following diagnostics/test.

1. Run the on board diagnostics and recovered codes 23 and 28

Pressure switch and rear solar sensor

2. Tested the pressure switch voltage which indicated there is sufficient pressure

3. Removed the connector on top of the compressor and supplied 12v directly to the magnetic clutch which enaged and the compressor stated running.

However, the air didn't seem as cool as it should in the front but in the rear (and in fridge) it seemed to be much cooler as you woud expect.

I also bridged connections 3 and 5 where the relay for the compressor goes which also engaged the clutch.

Not sure what I should do next, any advice?

TIA

[ambermarine]

Zia

There is another sequence in the process and that is the ambient temprature sensor in the cabin and on the front of the car these monitor the temprature outside and inside the cabin. This might sound obvious but they are programmed to switch off the A/C at set high and low extremes that occur in certain tropical and subzero regions to protect the system .

If either of these sensors are faulty the compressor will not engage.

They show up as codes on the self diagnosis but may still have a bearing on your problem even if they don't show.

The amount of gas for a full capacity on the 430 is around 36 ounces and 7 ounces of pag oil that makes 900g look short to me but I am an imperial Measure so I could be wrong.

[steve2006]

Do you have 12 volts on pin 1 of the AC relay (MG CLT Relay) ? With the AC off is this voltage also present on pin 2 of this relay?

Good suggestion from Ambermarine the ambient temp sensor can become clogged with fluff and provide false readings so a good idea to check and clean this ( I use compressed air in an aerosol). The external sensor has been known to either fall off the mounting behind the bumper or the wires corrode

If you PM your email I can scan and send you the Lexus manual section for the electrics involved.

[Suprazed]

Thanks both,

I have 12v at the a/c relay, this is identified on the fuse box cover as a/c compressor (I think) definitely doesn't say MG CLT. When I bridged it though the compressor kicked into life.

Steve, I'll. Pm my email (assuming I'm able to after just 3 or 4 posts)!

So do you think the ambient temp sensor could cause the front to produce ambient-like air while the rear has a/c air?

Cheers

[ambermarine]

Zia

I think what Steve is saying is that the ambient temp sensor in the cabin regardless of where it is could be faulty and may not be allowing the clutch to engage ,bearing in mind you are engaging the clutch by bridging the relay,so any results you may be getting in the operation of the system are compromised. ie; working in the back and not working in the front may have nothing to do with the sensor.