w1ayne

Recently I lent my 1991 LS400 (137K) to my bother-in-law for a week (in Oakland, CA). The AC had been working but when returned the compressor was (is) frozen and does not turn. I have not talked to him about it as I am trying to understand what may have caused it to fail. Could it have been his mis-operation of the controls? The AC was repaired in 2009 at 133K for $1400, new compressor, etc.

When it was returned, 3 of the 4 air vents on the dash were closed (too much cold air?) with only the right most one open. I do not know the temp setting as that readout does not show (a common problem with the LS400). The AC button was blinking (indicating compressor lock). If he had set the temp rocker to its lowest setting with the AC on and closed the air vents could this frost (freeze) up the evaporator to where the high pressure side would rise enough to destroy the compressor? Can the compressor be destroyed if the AC is left on its coldest setting in humid conditions and the evaporator frosts (freezes) over?

timmy0tool

iTrader: (7)

i have never heard of frost collecting inside the system causing issues, and especially not locking the compressor. i'm not saying it's impossible however. with all the vents closed, there should be no issue with a standard AC system.

first talk to your bro-in-law and ask about the situation. what kind of new compressor was installed in the system? OEM or aftermarket? was the condenser replaced at the same time? did the HVAC readout break before or after the AC was repaired, bc it would be hard for the AC tech to fix a system with broken HVAC controls.

dicer

I was almost in tears.
What ruins the compressor would be lack of lubrication. Have you tried turning it by hand?

w1ayne

The compressor does not turn even with a socket and ratchet on the 10mm bolt in the center of compressor shaft.

With the temp (and clock) blanked out as in this car, the way to control the temp becomes just like a less expensive car with no read out of the temp. Just move the **** or rocker up or down to adjust the temp while feeling the air coming out of the vents.

The bother-in-law has said he did not use the AC. This does not shed any light on how this happened. Only me and my wife drive this car, hummmm. I do not like to post unless something can be learned so I will report back after they take the compressor out.

dicer

And if it put metal into the system, you may end up taking out the dash and the evaporator to clean and or replace stuff.

djamps

Maybe junk from the old compressor made its way thru the system and eventually damaged the new one? Like dicer said, the whole system may need to be cleaned/flushed.

oldskewel

iTrader: (1)

Unless someone popped the hood and tried to sabotage it, I think it's safe to say that it is not possible to damage the system by manipulating the controls - even if trying to damage it on purpose. Just not possible.

Your post shows only 4k since the AC was overhauled. So maybe it's a new component failing.

I'll guess that when it was overhauled, they switched from R-12 to R134a. Right? It might help (also when you get more info) if you list what components were replaced in the switchover.

You mention not being able to turn the bolt with a socket. It could be that the bolt is not supposed to turn - it just holds the AC clutch on the compressor. So carefully checking for compressor lockup may require energizing the AC clutch so it is locked, then trying to move that pulley to see if it spins. Or something else. I'm mainly suggesting that your bolt test may not be valid.

Good luck fixing it, and sorry to hear of your troubles.

dicer

I know others may disagree but, if it is converted to R134 there are some components that need to be changed. As well as a reseal of the system, and a through cleaning of all parts of the system. The pump either needs to be replaced or taken apart and cleaned. All of the R12 lubricant needs to be gone. If this is not done somewhere down the road its going to mess up. If you can not grab and turn the inner part of the clutch by hand the compressor is toast.

paul29

Lexus has a TSB on updating the 1991 LS400 from R12 to R134a. Not much involved ie change out the receiver dryer, a few O-rings and add a certain amt of 134a compatible oil to the existing R12 oil. You do not remove the r12 oil. Then recharge with R134a. I am not at home at the moment or I would have the exact quantities and type of oil from the TSB to give you. I changed my 1991 LS in June and it works to about 90 to 95% effective of what it did with R12. My LS has the complete original ac system including compressor. A very easy and effective conversion.

dicer

Do the study the two oils are not compatible.
So let us know what the oil is, and that would need to be on a tag under the hood.

He says the oil has to be out but sure doesn't cover how to get it out. Good old internet.

oldskewel

iTrader: (1)

Here's the conversion TSB: AC001-98
R12 to R134a AC Retrofit form Lexus .pdf
My understanding in general is that the two types of oil are not compatible. BUT, this TSB does say that "There is no need to remove or flush R-12 mineral oil from the system." But it does say to not replace it once removed. Replace it with the R-134a-compatible ND-Oil 8. If it were my car, I'd flush it all out.

But I'm still fully running on R-12, so I would not really know. I got this PDF when I was considering my options a couple of years ago. Turns out keeping the R-12 going was pretty easy.

LS400FAN

oldskewel you are correct on the this issue. Here's my issue, the bearing on the ac pulley is working fine, however when I activate the ac compressor (pushing the ac button), the idle fluctuates and and the ac indicator light starts blinking, the book says the compressor is the problem. I plan to put in a reman, have you or anyone you know of had any problems with remans? Thanks in advance.

dicer

Depends, a reman can sometimes be better than new.