Another A/C Problem

Hi group!
1990 420SEL ---- It's 90 degrees --- With the A/C on, the temperature at the driver's side vent (58) is about 10 degrees cooler than the center (68) and
possibly the passenger side vent. The mono valve appears to work normally. The setting of the temperature control (which works) doesn't appear to make a difference. Are there vacuum driven vent doors in this auto? If so, could this be the problem? What should I look for and where should I look?
Thanks in advance.
John
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A low freon charge will cool only part of the evaporator so I'd first check the freon charge before tearing into the ducts and doors etc.
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T.G.
Bingo!
I had the A/C serviced this spring for the first time in 10 years because it wasn't as cold as it used to be. At the time they added a dye. I just checked as much as I can see with a black light, and sure enough, there's a small amount of glow just behind the compressor pulley.
Can you or anyone give me a ballpark estimate for parts and labor hours? Besides being a senior, I understand that Freon in dangerous so I'm not going to tackle it myself.
Thanks in advance.
John
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Probably around $1K USD (possibly more like $1,300 depending on how good of a deal your shop can get on the compressor). And if you haven't already been retrofitted for R134 from R12 you may have to add in some more.
Josh

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John,
I'm not so young myself.
I'd expect some leakage at the compressor shaft and suggest you shine the black light on the A/C plumbing as far as you can, if only to rule out other leaks before attacking the compressor.
Another possibility is a closed expansion valve; the only way to know that is from the system's pressures. The charge and compressor may be fine but reduced cooling results if the expansion valve is corroded.
My old 300SD had lame cooling this spring so I had it "topped up" (after 9 years) and it now cools perfectly. I considered having it converted to R134a but the subject never arose as R-12 was added. The technician told me that the price of R143a had more than doubled in the last year or so and that its cost advantage (over R-12) had nearly evaporated. I write this so you don't get "sold" a conversion to R134a on the basis of future cost saving.
Freon IS dangerous and it's now illegal for non-licensed mechanics, including DIY, to open the system. So you can research the parts cost but not fix it. Suggest you return to the shop that added the dye, play dumb, and see what they tell you. After you get their estimate remember that the summer heat will only last another 45 days or so!
Tom
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Tom,
I need some clarification on your previous post. You stated 'I'd expect some leakage at the compressor shaft '. Does this mean that that is where you expected the problem to be, or that a small amount of leakage is normal? Looking from the top, there is an oval area of dye about 1" x 1/2" on a raided boss. I haven't been under the car to check the fittings yet. It's been to GD hot to do anything but drink beer here in Northern CT the last few days.
John
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This is the site of a shaft rotating within a seal so, IMHO, a small amount of leakage is normal. That said, the leak on your compressor may be greater than "normal" due to wear of the seal, shaft and shaft bearings.
Once again, I suggest you look for other leaks before attacking the compressor, if only to eliminate all other possibilities and so be sure IT is the culprit.
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amount of leakage is normal. That said, the leak on your compressor may be greater than "normal" due to wear of the seal, shaft and shaft bearings.

compressor, if only to eliminate all other possibilities and so be sure IT is the culprit.
Tom,
The plumbing is OK as far as I can see it, but after crawling under the front of the car, I found lots of dye on the compressor, starting at the rear of the pulley. My local shop quoted me $700 for parts & $300 for labor. Does this sound reasonable?
John
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Sounds pretty pricey to me. I bought a rebuilt compressor for my '81 300D for just over $125, converted the system to R134a, changed the drier, vacuumed the system, put in new coolant and the system works perfect. Total cost, including a new set of 134a gauges was about $270 total. Of course this was a DIY project but A/C systems are not nearly as complicated as some would make them out to be.
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