JHart

I have a '91 LS400 w/155K miles. The air coming out of the passenger's side middle a/c vent seems (IS) colder than that coming out of the driver's side middle a/c vent. The dealer, who I have only spoken to (the car has not been checked out), says it could be the expansion valve or the evaporator. Also, he says that I will have to convert the system to the new refrigerant if I have the work done.

(1) Why would ANY problem with the a/c system cause the air in the two adjacent, middle vents to be of different temperatures? i.e. how does this system work?

(2) Has anyone had their system converted? My non-Lexus certified mechanic can still use regular freon. Would I be better off going this route?

Thanks for any advice that you have to offer.

Jody Hart

blkstealthpaid4

I had my mechanic convert mine for about $50 but the genuine process is about $500.I turned around quick when I heard that quote.

jberger

Be VERY careful when changing over from R-12. The main problem is the oils which are completely different and NOT compatable.

Most often, mechanics just pull out the R-12 and replace it with r-134, this leaves the majority of the oils in place which turn acidic and breakdown the evaporator core, lines and compressor seals.

it is best to have your unit flushed to remove the old oils and vaccumed for a long time before trying to convert. I'd also think you would need to replace the dryer to get them all out.

I don't know who makes the Lexus compressor, but i know Calsonic had major seal problems with early 90's compressors which were converted to 134. the 134 ate the seals.

Not to scare you, but it's not as simple as changing freon, there really needs to be more to it than that. If not, you are risking a replacement of the entire system once the corrosion occurs. Having seen this happen to a friend of mine, I learned it first hand. But hey, it sounded like a good idea.

blkstealthpaid4

Well I went the easy way and it worked for me.Yes, he is right have your system at least flushed out with the machine and oiled.My mechanic only let out the r12 by pressing the valve that pushed out the old freon.This is illegal.

JHart

Thank you for the reply. Although it was the Lexus dealer that advised regarding the conversion and, if I were to convert, I would have them do it, I, too, am extremely leary of switching to R134. Your advice regarding the compressor seals "seals" the deal (pardon the pun!).

Any info on why one middle vent woould be a different temp than the other middle vent?

Jody Hart

jberger

Jody,
If it's really a vent temp issue (You'd need to check both the temperature and the volume of air to know), then I don't believe it would be the compressor. Low freon symptoms would be reduced cooling across all vents or a mix of hot/cold air as the compressor cycled on and off again.

Sounds like the door/lever which mixes the air between the vents is stuck so one side is getting more cold air than another. But I don't have a diagram to know where to start looking.
Some AC systems have a diagnostic mode which should cycle the mixing door/lever as part of the test. If someone can tell you how to put your system in diag mode, it should be an easy check.

Why is the dealer saying he would have to convert the system to do the work?
That's crazy, it's legal to refill R-12 systems as long as you repair the leaks. But the cost of R-12 is sky high and rising.

I've kept it in my cars becuase it cools better than R-134 in older systems. Early R-134 systems didn't cool well, but the new systems (last couple of years) work fine even here in the South. But it is one expensive conversion.

good luck.

LEXTEK1

JODY,

THE TEMPERATURE DIFFERENCE YOU SPEAK OF ON THE 1ST GENERATION LS400 IS THE RESULT OF LOW FREON AMOUNTS. THE EVAPORATOR ON THIS CAR IS LARGE ENOUGH THAT AIR FOR THE RIGHT SIDE IS DRAWN FROM THE RIGHT SIDE OF THE EVAP. LOW FREON LEVELS COOL ONLY THE INLET SIDE OF THE EVAP AND LOOSE ITS COOLING ABILTY BY THE TIME IT MAKES IT TO THE OTHER SIDE. IT SHOWS UP MOSTLY ON THE CENTER VENT BECAUSE THE TWO VENTS ARE SEPARATED INSIDE.

THE OLD LS HAS SEVERAL PROBLEM AREAS WITH THE A/C. LOOK FOR THE COMPRESSOR HOSES TO LEAK ON CARS WHERE THE HOSES ARE SEVERAL YEARS OLD. THE EVAPORATOR IS THE MOST COMMON LEAKER THAT I HAVE SEEN.

GOOD LUCK.

JHart

Lextec1,

Thank you for your excellent explanation. This makes sense and I look forward to having it confirmed by my mechanic.

Sincerely,

Jody Hart