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1991 Ls400 A/c Overhaul And R134a Conversion


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I wanted to share my experience on refreshing my a/c system and converting from R12 to R134a on my 220k mile LS400. My decision to DIY was driven by the nearly $700 the local Lexus dealer charged to "repair" my a/c last year, only to give up when they could not get it to work for longer than a day.

I began by replacing the evaporator and expansion valve. It is a labor intensive job, but definitely not out of reach for an average DIY mechanic. From there, I removed the Evaporator Pressure Regulator (sometimes referred to as a suction throttling valve) and disassembled it (six screws). After inspecting the rubber diaphragm for any tears or holes, I reassembled with PAG 46 oil and a new o-ring on the spring-loaded "piston". This o-ring is like a compression ring, so to speak. From there, I removed and sent out any rubber hoses (discharge and suction at compressor and the suction hose sections between the evaporator and the compressor) to be replaced at a local machine shop that repairs a/c hoses. I was very pleased with the quality of the work; the assemblies looked very much OEM, at a savings of over 50% versus the best online prices for new hoses. With the system this far apart, it was very easy to flush the remaining parts (ie the condenser and small miscellaneous lines) with a "flush gun", that can be purchased / rented at most auto parts houses. I then replaced the compressor with a rebuilt unit from a gentleman in Texas, who was a wealth of knowledge and provided a great product. The last new part was a new receiver-dryer. When all of the parts were ready, I reassembled the system with new HNBR (essential for R134a) o-rings, including several seals where two pieces of tubing thread together (the service manual refers to them as Brock joints) and use o-rings to eliminate leakage. After reassembling, I pulled a vacuum on the system with a small vacuum pump for about an hour and a half, to ensure that all condensables were removed from the system. The system held this vacuum for 15 minutes, meaning no leaks. I then added about 28oz-30oz of R134a to the system with a set of manifold guages, to ensure that the high and low side pressures were within spec. The center registers now deliver air at 38 degrees when the ambient temperatures are around 95 degrees.

For those interested, here is a breakdown of the expenses involved:


Compressor: $200 (1yr warranty)

Rebuilt Hoses: $150

Evaporator: $130

Expansion valve: $36

Receiver-dryer: $15

O-ring kit: $6

Parts Total: $537


R134a: $21 (3 12oz cans)

PAG 46 oil: $9 (8oz)

Supplies Total: $30


Manifold Gauge Set: $50 (may be rented/borrowed)

Vacuum pump: $90 (again, rented/borrowed)

Leak checker: $75 (optional, but good for piece of mind)

I happen to own these tools, because I love to work on my own projects.

Let me know if you have any questions.


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Hi VH,

If I had a bet, I would say that your discharge hose at the compressor is leaking. It is nearly impossible to see the leak here, as the rubber hose is surrounded by a rubber sleeve, which obscures any visual observation. I got my leak checker on eBay...or you can use UV dye, which is added to special cans of R134a.


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jeffls400 ... just a quick comment to say that your posting on your A/C system was GREAT. Thank you !!!

I wish I was your neighbor ... I would love to pick your brain about changing out my suspension bushings and doing all 4 strut replacements on my 95 LS ... I do not know how much pizza and beer would be required ... but I would gladly buy! hahah! Suspension stuff is far from anything having to do with A/C ... but it sounds like doing what I need done would be easy for a person like you .... no matter what, I am going to learn how, buy the tools, and do it my self .... I am so sick of paying absurd labor costs.


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  • 5 years later...

Hey, jeffls400, I agree totally about the absurd costs! My wife's car is a 1991 Lexus LS 400 that I bought 6 years ago for $2,400. She went shopping today and when she came out, the car would not start. So, I will get out my Ohm Meter and disband one thing at a time. I am almost positive it is the Solenoid or the Starter Relay Switch. While I am under there I am going to pull the AC Compressor and rebuild it! Never done one, but using the Forums I find on here, I can do anything! Chilton's and Hayne's do not publish a Manual for Lexus. You have to go to the Dealer and they cost about $275.00. I used to hang around the Pits at Tampa Speedway and they taught me a lot about Auto Mechanics. I have already pulled the Steering Rack & Pinion and rebuilt it! Almost lost my Religion doing that task! Anyway, Good Luck--and by the way--If you do the Struts yourself--make sure you use the proper tools and have a friend hang out with you! Strut removal and replacement is about a level 10 job and people have got killed trying to DIY! So, be very careful my friend!

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