91 350SDL / AC system rebuild - PeachParts Mercedes-Benz Forum

compu_85 · #1 05-03-2013, 06:26 PM

I'm doing an AC refresh on my SDL. The compressor on the car I think was original to the body (230k miles), and seemed to have wayyyy too much resistance when engaged. It cooled OK, pressures at idle didn't seem fantastic but were fine when moving down the road.

At $200 for a new Denso rebuilt one, I decided to just replace it. I took the old one apart to see what was going on inside.

Looks like there was some moisture in the system at some point:

There was also a nice wear mark on the swash plate:

All the bearings looked good though

All the valves look OK as well.

Each piston has 2 dome shaped tappits with a flat side that ride along the swash plate. The flat part is plastic, perhaps Teflon?

There was almost no clutch material left, but it wasn't slipping even with the extra drag.

There was a light film of black gook on everything inside, hopefully AC flush can remove that from the condenser and evaporator.

After seeing the wear I don't feel bad replacing the compressor. Hopefully the new one gives me nice ice cubes from the dash

This one might be rebuildable. I may look into that later.

I took some videos too, I need to edit them together. I'll post that later.

Thanks,

-Jason

compu_85 · #2 05-05-2013, 08:20 PM

I was really proud of myself... I got the radiator / trans cooler lines and condenser out without stripping any of the rusty fittings. The large fitting on the condenser put up a good fight.

Then I pulled the fans off the condenser and found some bad news

Looks like there was galvanic corrosion between the condenser and the fan motors. perhaps the oily gook on the fins held winter salt against the metal?

SO... I suppose that leaves me at a quandary: Do I install a modern parallel flow condenser? Get another tube and fin one? I was planning on regasing with R12...

-J

vstech · #3 05-06-2013, 09:17 AM

bump

compu_85 · #4 05-06-2013, 09:24 AM

So it looks like I can get a "direct replacement" parallel flow condenser made by "American Condenser" from worldpac for about $200 cheaper than a new tube and fin. Should I go with that and R134a? I'm using the compressor for the later factory 134a cars, so I'm thinking it should cool good (every 134a W124 I've been in has amazing AC, even at idle).

PS: Thanks for the title change

-J

upshift · #5 05-07-2013, 09:10 AM

I've converted a decent number of old BMW's and Benzes to 134a.

I always replace the receiver dryer, and I pull a vacuum on the system for at least an hour. I use Ester oil and use 80% of the R12 capacity in 134a.... every system I have ever converted blows just as cold as R12 did.

I've read comments that conversions don't blow as cold but after doing 6 or 7 cars, I have to disagree. I think it's just a matter of doing things right.

compu_85 · #6 05-08-2013, 10:22 AM

So I've been offered a good, used tube and fin condenser from another 91 350. I want the best AC possible for dealing with humid DC summers... The tube and fin will be less than half the cost of the parallel flow condenser.

Which would our AC Shop guys recommend I install?

-J

daw_two · #7 05-08-2013, 10:35 AM

Quote:

Originally Posted by compu_85

So I've been offered a good, used tube and fin condenser from another 91 350. I want the best AC possible for dealing with humid DC summers... The tube and fin will be less than half the cost of the parallel flow condenser.

Which would our AC Shop guys recommend I install?

-J

I would go with the 91 350SDL condensor because you already know the stock configuration is good enough.

Disclosure: I have a used condensor for sale. Keep reading for the conditions that would make me go with an upgraded condensor.

NOW, let's say, you live in Baton Rouge, LA or Memphis, TN or Houston, TX. And your car is used to carry 3 other guys (plus you) wearing business suits to lunch (or dinner) in the summer, then you might want to do everything possible to make it as cold in the cabin as quickly as you could. Given this: I would probably change to a parallel (or triple) flow condensor, upgrade the compressor, run the biggest, fastest fans out front on all the time, etc. And don't forget to clean the evaporator!!! It doesn't matter what you do under the hood, if you have an evaporator that looks like this, not very much cold air is going through it:

compu_85 · #8 05-08-2013, 12:05 PM

Well I'd like it to work a bit better than it did before

Remember it gets very hot and very humid here... 100*F and 90% humidity is possible.

I did already clean the evaporator the best I could with it in place... then looked with with a fibrescope. Can't say I looked all the way back in the far side though.

Hm is this going to turn into one of those "while you're in there" projects :S

-J

daw_two · #9 05-08-2013, 12:20 PM

Quote:

Originally Posted by compu_85

Well I'd like it to work a bit better than it did before

Remember it gets very hot and very humid here... 100*F and 90% humidity is possible.

I did already clean the evaporator the best I could with it in place... then looked with with a fibrescope. Can't say I looked all the way back in the far side though.

Hm is this going to turn into one of those "while you're in there" projects :S

-J

I'm guessing you noticed I really cleanned the evaporator on my AC manual airbox project.

It's probably going to work better since you cleaned the evaporator, condensor, wire the fans to blow on high, rebuild the compressor.....at least that's my opinion.

compu_85 · #10 05-17-2013, 09:30 PM

How much oil does the 126.135 AC system hold? Every document I look at seems to have a different number and there's no mention in the service manual for anything after 1985, and of course it's not listed on the under hood sticker. The place I got the compressor from suggests 4oz

-J

DeliveryValve · #11 05-18-2013, 12:44 AM

Seems like 7.75 ounces is the magic number.

Find your vehicle's refrigerant or oil capacity || TechChoice Parts
http://www.discountautoac-compressorparts.com/RefrigerantOilChart.pdf

.

Brian Carlton · #12 05-18-2013, 09:52 AM

Quote:

Originally Posted by compu_85

Well I'd like it to work a bit better than it did before

Remember it gets very hot and very humid here... 100*F and 90% humidity is possible.

I did already clean the evaporator the best I could with it in place... then looked with with a fibrescope. Can't say I looked all the way back in the far side though.

Hm is this going to turn into one of those "while you're in there" projects :S

-J

Firstly, the condition of the old condenser was not all that bad. Most of what was seen in the photo is accumulated dirt. Once cleaned, there is only a very small section where the fins have corroded slightly..........will affect cooling nearly insignificantly.

The Nippondenso and the evaporator on that vehicle does a good job with R-134 and I'm sure it will be perfectly adequate at 90 degree ambients. However, if you want stellar performance at 100 degrees, you should really consider going back to R-12. Since the system is completely torn apart and you're going to flush it anyway, I do not understand why you wouldn't use R-12. I found a case of it for $200 on e-bay, enough to do three vehicles, so cost cannot be an argument. The only issue might be servicing in the future. Most shops hear the word "R-12" and run for the hills. This might not be an issue for you.

compu_85 · #13 05-19-2013, 11:01 AM

Ya, I suppose the areas where the fins are gone isn't super huge:

But a new condenser wasn't that expensive.

One thing I didn't notice before... my car originally had a parallel flow condenser! The new condenser is 1/2" narrower, and 1 row shorter than the original.

compu_85 · #14 05-26-2013, 11:37 PM

Made a lot of progress today... compressor refilled with the proper quantity of oil, TX valve changed, everything flushed out, trans refilled... ran out of daylight.

One thing that I found interesting is that the TX valve is actually adjustable:

You can grab the brass round bit on the right with a pliers and screw it in and out. This changes the preload on a spring pushing on the seat for the needle in the valve. The new valve I put in had two little holes for a spanner wrench.

Side note: Those fittings on the TX valve are a real PITA to deal with.

-J

compu_85 · #15 05-27-2013, 05:26 PM

Charged with 26 oz of R152a. Vent temps are in the upper 40s, and it doesn't feel like you've thrown out an anchor when the compressor cycles on. It's actually hard to tell when the compressor is running and when it isn't!

I'll see how it performs as the weather gets hotter.

The aftermarket condenser didn't clear the fan shroud properly... Not a huge problem in my case as ill be installing some electric puller fans soon and removing the pusher fans. I trimmed the shroud so it can be removed with the condenser still mounted.

The R152a cost me $30

-J

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