frozen A/C compressor. . now what - PeachParts Mercedes-Benz Forum

BrianCostello · #1 05-29-2011, 12:26 PM

Well now that summer has arrived in New England I decided to turn the A/C on in the 1987 300D.

It was working great last summer. . .this weekend not so much.

I notice that the compressor was not engaging, so after a little search here I start to check out the KILMA relay.

I decided to jump pins #5 and #7 to force the compressor to run (and find out if I had a bad compressor or bad kilma)

Doing so the compressor froze up immediatly . . .and snapped the serp. belt.

So I now need a new compressor, and am looking for the proper replacement procedure. and suggestions on what else to test (besides freon levels of course) to make sure that I don't destroy the soon to be installed new compressor.

The car is already 134a.

Brian

Matt L · #2 05-29-2011, 12:38 PM

Flushing the entire system is required. Including the evaporator, as sometimes compressors will spew a bunch of junk to the inlet when they let go.

I believe that you have a tube-and-fin condenser, so you can flush it (parallel-flow condensers should simply be replaced). Mufflers should be replaced; is there one on your inlet line? Those are pricey. Some people cut the mufflers out rather than replace the line.

leathermang · #3 05-29-2011, 01:32 PM

A good time to remind everyone that most AC instructions say to turn on your AC once per month even in the winter... which helps keep the seal at the shaft lubed...and expanded....

Codifex Maximus · #4 05-30-2011, 12:39 AM

Yeah, doesn't the non-economy setting use the compressor to remove moisture from the air prior to heating in the winter?

leathermang · #5 05-30-2011, 02:54 PM

Quote:

Originally Posted by Codifex Maximus

Yeah, doesn't the non-economy setting use the compressor to remove moisture from the air prior to heating in the winter?

Some cars certainly have that nice feature... which should provide that function without people having to remember to turn the AC on in the winter..
but I am not sure all cars have it. I think it is wired to the defroster in the cars I have ( non MB )....

kickit · #6 05-30-2011, 04:07 PM

Brian: Definitely start out with the DIY thread http://www.peachparts.com/shopforum/showthread.php?t=142408

When I had my 300SD, I replaced the compressor, dryer and evaporator valve and flushed the condenser and evaporator while the parts were removed. All recommended by this forum. The evaporator valve on my 300SD was a real PIA to replace, tucked up above the accelerator pedal.

Fluids you'll need are flushing fluid, oil for the compressor, and of course R134.

Tools you'll need are a vacuum pump (I've seen them for ~$100), a gage set (~$50 at Harbor Freight) and a crows feet wrench set for the evaporator valve (Did I mention that one is a PIA!). And an air compressor.

Not sure I would do it again if I had to, but hey, if you have the time and patience...

I may have forgot a couple things, but those are the big ones.

In general, you remove the pump, dryer and evaporator valve. Put the flushing fluid in to both the evaporator and condenser, let it sit and blow it out with air going both directions. Depending on how clean it comes out, you may need subsequent flushes. Once the fluid comes out relatively clean, blow it out with air real good to dry both.

Install the new pump, dryer and evap valve. Add oil to the pump. Tighten down all connections. Install the gage set and hook up the vacuum pump and let it pump down for awhile. You will be removing any residual moisture at this stage so keep an eye on the vacuum oil. If it gets cloudy, it means you are taking on water and you should crack an upstream valve to allow in a very small amount of air. This will help purge any water from the vacuum oil. Keep purging until the oil clears, close the 'leak' valve. What you want is to be able to pull a full vacuum for an hour and have no water in the oil. Then you test the system by closing a valve to the vacuum pump on the pump side of the gage set, turn off and open the vacuum pump to air. The sealed off refrigerant system should hold a full vacuum for at least an hour (I tested mine overnight).

Then it's a matter of charging the system with R134 and using the gage set to make sure you do not over pressurize it. The gage sets usually have some instructions on how to use them.

BrianCostello · #7 05-31-2011, 10:06 AM

thanks for the informative replies! love this forum!

Over the long weekend I put on a spare serp. belt and fired up the car. good news is that the clutch is working fine, so now I can run the car.

I plan on gathering all the parts I need this week, including a few new lines (mine are original as far as I can tell)

Where is the evap valve of the W124?? I could not see it, so whats is hiding under?

I plan to clean the evaporator (hopefully getting away with not replacing it) As I said the AC was fine last year, no signs of a overly poor operating system. It maintained a 30 degree delta T.

And with the car running, I will take it to my local indy who is also a friend. Have him evacuate the system. Then I take her home and replace all the parts I need to, and clean the evaporator. Then back to my Indy for a flush, vaccum test, and re-fill when ready.

so yeah, where's that evap valve??? the compressor looks easy to get out, is it?

Brian

jcyuhn · #8 05-31-2011, 10:39 AM

Quote:

Originally Posted by BrianCostello

thanks for the informative replies! love this forum!

Over the long weekend I put on a spare serp. belt and fired up the car. good news is that the clutch is working fine, so now I can run the car.

I plan on gathering all the parts I need this week, including a few new lines (mine are original as far as I can tell)

Where is the evap valve of the W124?? I could not see it, so whats is hiding under?

I plan to clean the evaporator (hopefully getting away with not replacing it) As I said the AC was fine last year, no signs of a overly poor operating system. It maintained a 30 degree delta T.

And with the car running, I will take it to my local indy who is also a friend. Have him evacuate the system. Then I take her home and replace all the parts I need to, and clean the evaporator. Then back to my Indy for a flush, vaccum test, and re-fill when ready.

so yeah, where's that evap valve??? the compressor looks easy to get out, is it?

Brian

The expansion valve is located next to the brake master cylinder, just towards the middle of the car. It's in plain sight, so not difficult to locate. It looks impossible to work on, but in actuality isn't all that bad - so long as you don't have gigantic hands.

I think it's a single 8mm nut clamping the high/low hoses to the front side of the TXV. Once removed, it exposes two 3mm allen head bolts which secure the TXV to the evap inlet/outlet pipes. Hopefully nothing is seized - I've had to drill one of these out, and that *was* a drag. If the 3mm bolts are tight, feel around to the back of the TXV where they thread through a plat that holds the TXV to the evap, and try to get a little lube on the threads.

My tip for the day...

- JimY

BrianCostello · #9 05-31-2011, 01:00 PM

Quote:

Originally Posted by jcyuhn

so long as you don't have gigantic hands.

- JimY

great tip!thanks!

bubt yeah I do have gigantic hands. .

6'4" 220lbs and a size 14 shoe. . hands to match

Brian

JHZR2 · #10 05-31-2011, 02:32 PM

Running AC is absolutely an important thing to do YEAR ROUND. Keep that in mind.

JHZR2 · #11 05-31-2011, 02:35 PM

Quote:

Originally Posted by leathermang

A good time to remind everyone that most AC instructions say to turn on your AC once per month even in the winter... which helps keep the seal at the shaft lubed...and expanded....

Question for you - why is it that my window AC units get only at best three months of use, and even then range only from once a day to maybe three times for the season... Yet I have 20yo units that still work beautifully?

Is it because the system is soldered shut vs. o-rings? if so, why not use that technique on some of the auto sections? Even if a tech is needed to do it, so what?

vstech · #12 05-31-2011, 05:36 PM

Quote:

Originally Posted by JHZR2

Question for you - why is it that my window AC units get only at best three months of use, and even then range only from once a day to maybe three times for the season... Yet I have 20yo units that still work beautifully?

Is it because the system is soldered shut vs. o-rings? if so, why not use that technique on some of the auto sections? Even if a tech is needed to do it, so what?

it's a few reasons.
1. window units do not have portions of the system mounted on an engine, and portions mounted under a dashboard, so no flexible hoses are needed.
2. the all metal lines are soldered with high temp solder for a permanent seal.
3. the compressor is sealed into the lines with no protruding shaft that's belt driven...

BrianCostello · #13 05-31-2011, 08:49 PM

I know all about how your supposed to run the Ac even in the winter. . .

but I DONT drive this car in the winter. I fixed the small amount of rocker rust it had. now she's the garage queen.

I drove it for two weeks this winter before I picked up my beater wagon. I washed the road salt off by hand with a rag this Spring.

Parts ordered. I'll take some pics of my tear down/rebuild and post them up to help other find components, etc...

Brian

1980sd · #14 05-31-2011, 09:02 PM

Quote:

Originally Posted by vstech

the compressor is sealed into the lines with no protruding shaft that's belt driven...

Always wondered about that. It's like a ball with 2 tubes and some wires coming out...

jcyuhn · #15 06-01-2011, 10:56 AM

Quote:

Originally Posted by BrianCostello

I know all about how your supposed to run the Ac even in the winter. . .

but I DONT drive this car in the winter. I fixed the small amount of rocker rust it had. now she's the garage queen.

I drove it for two weeks this winter before I picked up my beater wagon. I washed the road salt off by hand with a rag this Spring.

Parts ordered. I'll take some pics of my tear down/rebuild and post them up to help other find components, etc...

Brian

Depending on what passes for winter, the ac doesn't run anyways. The vapor pressure of the refrigerant declines at lower ambient temperatures. At a specific temperature - generally around 32F - the low pressure cutout switch is triggered and the compressor doesn't run anyways. There's really no need to dehumidify the defrost air when the dewpoint is below freezing...