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Matt, Engineer
Category: Lexus
Satisfied Customers: 21863
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Customer Question

Submitted: 1 year ago.
Category: Lexus
Expert:  Don - Mo Lurch replied 1 year ago.

What is your question??
This is all that shows:

Country:United States




Already Tried:see above



Customer: replied 1 year ago.
ok. so are you my 'real' mechanic? I am frustrated by the way justanswer does this, which is bait and switch. I have paid the fee - am I really working with a real lexus mechanic now - can you tell me?
Customer: replied 1 year ago.
1999 Lexus es300. No cold air. clutch not kicking in. Used to work. This is consistent. Our (generally) very good mechanic said they they traced it down to this: the plug has 3 wires in it (going to clutch). We checked that plug just now - 2 of them with AC off have 14V. The 3rd one - nothing. With AC on, no change. He said we needed a new compressor. We had another mechanic put a brand new compressor on it, new drier, pulled a vacuum, charged it. He said he jumped the relay and it worked - said we needed a new relay, but we replaced that and it still doesn't work. Still the voltages I mentioned above. We can try swapping this 'new' relay with the other relay like you mentioned below. We can check the freon level, but I doubt that's it. Do you have any ideas? We are willing to pay if you can help us, sir.
Expert:  Matt replied 1 year ago.


another expert here

I'd say its likely that the freon pressure switch is faulty

ideally if you were have the car plugged into a dealer level diagnostic tool then you should be able to see if the pressure is registering on the system

as it seems that a fair few parts are being replaced on a hit and hope basis so far

although admittedly the switch is a cheap part

Customer: replied 1 year ago.
I hooked up gauges. initial static pressure is 100 on the low side. We bypassed the relay and the AC works just fine and pressures are good. However, the relay is not bad - we know that - after spending $30 on a new relay. So do you still think it is the Freon pressure switch? Are you saying that the switch is basically lying to the system and saying then that the pressure is low when it really isn't and therefore won't send a signal to the relay?
Expert:  Matt replied 1 year ago.


Ok the pressures may be fine but if the pressure switch on the high side is faulty then the relay will nver be powered

if you were to disconnect the switch and fit a jump wire into the socket to see if the compressor kicks in

Customer: replied 1 year ago.
ok. so can you tell me where the pressure switch is located? on top of the dryer? After doing some reading, it appears to me that there are 4 wires in that connector and we need to jump 2 of them to bypass the switch? Which 2? The 2 middle ones I think (1 and 4) are going to the AC clutch circuit - so we would jumper those 2?
Customer: replied 1 year ago.
We just jumped 1 and 4 and nothing happened - no clutch still. So it apparently is not that switch. Is there another pressure switch?
Expert:  Matt replied 1 year ago.


the switch is tucked away just inside the front bumper

see the attached image for its location

if you jump pins 2 & 3 they are for the AC cooling fan and 1 & 4 are for the AC compressor

Customer: replied 1 year ago.
Like I said, we already tried that and nothing happened. So it is not the pressure switch. What next?
Expert:  Matt replied 1 year ago.


its looking like the AC control unit may in fact be faulty then

I'd go back to the pump relay socket and see if there's power at the socket on the switch terminal once the AC is enabled

Customer: replied 1 year ago.
I really need details and clarifications here. First of all, what and where is the AC control unit? Second, what pump are you talking about? you mean the compressor? Are you talking about the MG clutch relay? What switch terminal and which terminal - and what do you mean 'enabled.' This means nothing to me.
Customer: replied 1 year ago.
I would like to have a new expert please. I am not satisfied with the expertise level of Matt. This is wasting my time... thanks.