Mark Manzo

I was asked to work on my sister's AC on her 1991 LS400. Here are the symptoms:

- AC does not blow cold, not even slightly
- Compressor runs when AC is activated. Clutch pulls in. Physically see compressor turning. Does NOT cycle
- Attached guages to car - Both high and low side read 100 psi. Compressor does not seem to be pumping
- A/C hoses do not change temperature tot he touch.
- Checked codes on HVAC unit. NO codes and NO flashing AC light
- Car has only 75,xxx miles....


What do you think? Compressor pulls in, I feel the car take a lite load but no cold air. Is it bad compressor? Clogged tube and/or expansion valve?

Before I start tearing the system apart I thought I would get a response from the Forum.

Also, how bad of a job is it to replace compressor? I have not looked into this yet.

All responses welcome....

Tammy

My suspection is the system is empty of freon, since both high and low guage the same pressure.

Air condictioner systems are for trained personnel. It can be physically dangerous. Small leaks can be hard to locate, thus expensive to fix.

I believe your 1991 system uses the R12, not the R134a type of freon. A label under your hood is mandated to inform you. Unless you have a EPA Automobile HVAC certification, with the card, ( I humbly do ), you cannot purchase R12 by federal law. It is expensive, by the 5 gallon tank; up to hundreds of dollars, new. Almost all available in the US today is recycled.

You'll need a freon leak detector and the green dye. A supply of compression fitting seal rings.

Normal system pressures are : Low 21-28 psi, High 206-213 (per Lexus TSI document # AC93-003, dated April 16.1993, supporting the R12 systems)
This is a vacuum evacuated and then fully recharged system; compressor operating. Few or no bubbles in the sight glass.

A consideration is an A/C specialist shop in your local area, who can test your system for leaks without using freon. The most common is a rock leak in the front condenser. Next is the compressor drive shaft seal, behind the clutch. This sometimes fails with a too tight belt on the older seal. If either replacement is needed, weigh the conversion cost to R134a refrigerant. The dryer should always be replaced with an evac & recharge of the system.

The job will then be warrantied for your sister .... "this is a good thing when it comes to aged A/C systems" ....you'll be a hero

Mark Manzo

I disagree. There is freon in the system. Otherwise I would read 0 psi or low psi . I am reading 100 psi on both low and high sides. The compressor runs. It does NOT shut off under loww pressure.

It is R12 and I am EPA Certified to work with and purchase R12 for Automotive applications. I can tell you my sister had a leak test done and the mechanic found no leak. (She was traveling at the time)

As for the pressures as per Lexus Service Bulletin, they seem to be in line.

I also agree with with replacing the dryer.

I have determined the compressor is shot. It is just not "compressing". I am going to evaluate what the cost of replacing the compressor, converting to R134, the cost of the dryer and possible replacement of the expansion valve and compare it to what the car is worth. My sister is thinking about selling the car and this just may make her decision easier.

I have worked on many AC systems in the past but this is the first I have seen where compressor runs and no pressure being built at all when comparing low to high side. This is the reason I am asking the forum.

Thank you for your response.

JUSROLLIN

Take it for what it is worth. I am not licensed, or qualified to service AC systems, but I have switched 2 cars (including a 92 ES300) to R134a after they got low on the old stuff, by simply pulling the valve stem (letting the old charge disperse which is illegal by the way), and recharging the system (1 can oil, the rest R134a) with an adapter to get it into a valve stem, instead of the new fittings. I never pulled a vaccum, and never replaced a single part. Both cars that I serviced this way had ice cold AC for 20k+miles before I sold them. It's probably not the "right" way to do it, but if it works, why spend all the loot?
Brandon