WYIN : AC Components to Replace?
 

I'm not getting any cold A/C at the moment, so I'm planning to do some diagnostic work.

Last time I had it filled at a shop, they said "high side a little too high, low side a little too high". They suggested the condenser could be replaced. The compressor was replaced 3 years ago.

I'm wondering what else I should do "While You're in There (WYIN)"?
- Condenser
- Expansion valve (where is this on the car?)
- Receiver / Dryer?
- Any extra o-rings?

Any other components?

Bruce

Before touching a thing, stick a manifold gauge on there and find out what's currently happening with your pressures!

High on the high side and high on the low side suggests it was overcharged.

Start w/ the basics. Is the compressor turning? Look at it. The pulley always turns w/ the belt. The compressor turns when the outer section of the clutch turns once the clutch is engaged. If not turning, you sure won't get any cooling. If turning, is the suction line getting cold. If so, perhaps your heater is on and over-powering the AC. That is a common problem in W123 cars. When not moving, the AC doesn't cool very well. That is very noticeable in my 2002 T&C as well. I verified that the electric condenser fan turns on in both vehicles, but that doesn't cool it near as well as the air-flow when the vehicle is moving.

"Before touching a thing, stick a manifold gauge on there and find out what's currently happening with your pressures!"

READ THIS, AND THEN READ IT AGAIN, then DO IT. Until you can look at the gauges and read the pressures and temperatures, you are guessing. If it's 110F outside, then BOTH sides are going to be a little high, that's how gas pressure works. If it's high on both sides and it's not hot ambient, the gas pressure is too high... overcharged. At least you have some leeway on a Benz system. The Toyota I worked on recently was 14oz, TOTAL, +-0.2oz.

OK, gauges have been ordered and are en route.

I put the AC on with the car in the garage and shot this video. It is difficult to shoot in there! https://www.youtube.com/watch?v=2ui7-KtopyE

I couldn't quite tell if the outer was turning. There was definitely an a portion of the bore I could tell wasn't turning.

I left it on for about 5 minutes, which never engaged the secondary electric fan. Also after 5 minutes, I felt both of the lines, but neither of them was appreciably colder. Is the suction the line that goes from the low side fill port to the compressor?

The compressor is not engaged in your video. The center part of the hub will rotate when the clutch engages.

Suction line is the heavy line, larger diameter leading straight back to the compressor.

When your gauges come in, check standing pressure in the system. If you have good standing pressure, you can troubleshoot further electrically. If you have low or no standing pressure, time to do some leak hunting.

OK, gauges went on this morning. Showed absolutely no pressure, BUT compressor still not coming on.

To verify the procedure :
- I connected manifold lines to quick disconnects and manifold set. I checked that manifold knobs were closed and quick disconnects were open.
- I connected both quick disconnects to the high and low ports on car.
- I turned car on, set to max cold, AC on, and blower on high.

The gauges showed no change from when they came out of (expensive!) box.

Should they be indicating some sort of standing pressure, even with the AC compressor not cycling?

Looks like you're completely out of refrigerant, yes you should have a standing pressure even with the compressor stopped. You have a major leak somewhere that needs to be found! There's a pressure switch in the system that prevents the compressor from enabling when the refrigerant pressure is low, it saves the compressor from destruction. Sounds like it's doing its job.

It seems that all your refrigerant has leaked out. That is "standard operating procedure" for a car with an R4 compressor and 30+ year old hoses.
Time to do what Diseasel300 has said (I agree)- check for leaks.

EDIT: Diseasel300 you are too fast for me!
EDIT #2: It was pointed out in post #14 that the vehicle has a Denso compressor, so I take back what was said about the R4 and 30+ year old hoses.

OK, so I'll order a UV light - there was dye put in last time I had the car filled (2 years ago, 5k miles)

If I'm going to open the AC system up at this point, any reason to have a shop evacuate refrigerant, or is it functionally all out of there (if for example I find a big leak on condenser).

For interest, the system was updated to R134a in 1997, and got a new compressor in 2016.

I presume there is no possibility this is an electrical error at this stage? I had replaced a relay for the aux fan in the spring.

You asked if any other components needed to be replaced "While You're in There".
Now that you know you have a leak, I would suggest a complete system rebuild. In my world that consists of a Sanden retrofit, all rubber hoses replaced (no need to replace the liquid line), condenser, and of course drier, pressure switch, and TXV. After removing all the old components, the evaporator should be flushed, as well as the remaining liquid line. All the new components installed with the drier uncapped and hooked up LAST. Drain compressor of all it's oil unless it already has Ester oil in it. Then pressurize the system with a dry gas and check for leaks using soap and water solution. Pull a good vacuum, and then charge with your refrigerant of choice. R134a is adequate with a parallel flow condenser, but R12 would be better with either the factory tube and fin, or P.F. condenser. If you want to roll the dice on an R4 (new or reman), I suggest all the above (except the Sanden of course) and R12.

No reason to evacuate something that is not there. Also, it wouldn't hurt to have a UV light to check for leaks in the future.

There's no point in evacuating anything at all. You have nothing to evacuate!

Since you had dye, get the UV light and see if you can find the leak. Cross your fingers it isn't in the evaporator!

Things to replace? Every single rubber O-ring you can get your fingers on. ALL OF THEM. If they weren't replaced before, they're probably crapped out for sure by now. Also the filter/dryer. It should be the very last thing to go in, immediately before you have it pumped down in a vacuum prior to filling with refrigerant. Unless you find evidence of hoses leaking, leave well enough alone. The paranoia about hoses leaking is way overblown IMHO.

Rollguy: This is a W201, he should have a Denso and a system that should be able to handle R134a in its stock format.

Ahh, missed that:(. I take back everything I said (well most everything). I agree about every Oring, and add that the compressor manifold seal (not exactly an Oring, but made of the same material) should be replaced as well. Did the system originally come with 134a? If it had R12 from the factory (I assume this), then it probably had mineral oil. I don't know for sure, but MB might have gone with Ester in the Denso compressors then, and that would be good. If it had mineral oil, and was retrofitted to 134a, that would be a problem.