91 350SDL / AC system rebuild - Page 2 - PeachParts Mercedes-Benz Forum

strelnik · #16 05-28-2013, 09:30 AM

Quote:

Originally Posted by compu_85

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

Terrific, I wish I could get someone to help on the AC on the 126 I have, which I ove to drive.

compu_85 · #17 05-30-2013, 12:13 PM

Some results from the drive in today: Outside temp gauge hovered around 90*. While moving the vent temp stayed around 49* (clutch cycling)

However, when the RPMs get closer to idle the cooling drops off quite a bit and the vent temps climb into the 60s. It's not an airflow issue as I'm not running a mechanical fan. As the RPMs rise I can hear refrigerant begin to hiss through the TX valve.

I'll have to put my gauges back on and check pressures.

-J

Brian Carlton · #18 05-30-2013, 12:21 PM

Quote:

Originally Posted by compu_85

. While moving the vent temp stayed around 49* (clutch cycling)

-J

Not cool.

The ETS is tripping the compressor to cycle off way before it should. You want those vent temps down about 40F.

The only reason the vent temp should not hold 40F. is if the compressor is at 100% duty cycle and it simply cannot keep up with the heat loads.

You might want to jump the ETS and really see how it will perform without any restriction on the compressor. Of course, you cannot leave it that way or you risk freezing the evaporator and then all cooling goes to hell until it melts.

compu_85 · #19 05-30-2013, 12:52 PM

GenII car's use an electronic temp sensor and the digital ACC computer cycles the clutch. I suppose it's possible my temp sensor is bad, but I also don't mind an even 50* air from the vents... any colder and my hands start hurting. But for a quick test I can just pop the temp sensor out of the HVAC box. I'll do that on my drive home.

-J

Brian Carlton · #20 05-30-2013, 01:01 PM

Quote:

Originally Posted by compu_85

and the digital ACC computer cycles the clutch.

-J

If you've got a digital ACC computer on the '91, that would be the first I've heard of it.

The '87 has the standard analog CCU control in the dash.

compu_85 · #21 05-30-2013, 01:21 PM

The late cars ACC looks just like the early Gen2, but is actually digital and can generate fault / blink codes. It still uses the Price Is Right temp dial though (and the pot on mine is dirty and needs cleaned / replaced

)

-J

BrianCostello · #22 05-30-2013, 09:29 PM

Jason:

Correct me if I'm wrong (which I may be)

In the original set up. The fans come on low speed when the refrigerant switch makes. And high speed only when the high temp switch makes. When the high temp switch makes, it also shuts off the compressor via the kilma.

So if that's true, then with your modified fan control when the fans go to high speed, they are telling the compressor to shut off???

Just a thought. Because you kept all the factory relays in place, when you sit in traffic and the fans go to high speed, you might be killing the compressor.

Brian

compu_85 · #23 05-30-2013, 10:30 PM

Not quite true on the later cars: there is no high temp switch, there is a temp sensor that the ACC uses to control things. It turns the fans on high before it kills the compressor.

That does make me ponder a bit though... I swear I could hear the refrigerant hissing more then less on the drive home, with the evap temp sensor hanging free. I'll have to put a test light on it...

-J

compu_85 · #24 06-01-2013, 09:59 PM

Diddled with this a bit more tonight, I removed some gas from the system and that improved vent temps.

I did notice something concerning though. The fan relays are getting really, really hot. So hot in fact the 40 amp fuse on the high speed relay melted:

I measured the draw of the fans, they draw 10 amps on low and 23 amps on high.

Both relays are rated for 40 amps, so I'm not sure why they're getting so dangerously hot.

I may have to ditch the stock fan controls and use some other method to control the fans

At least the 110 amp alternator is kicking butt at idle:

-J

hapaschold · #25 06-04-2013, 10:48 AM

thanks for the great pictures and dialog on your work...

the ac in my 350sdl been acting up, still on r12, used to make ice cubes outta vents, but now compressor cycling on and off frequently...

have klima relay coming in, going to try that, if not off to the indy repair shop i guess....

compu_85 · #26 06-05-2013, 06:05 PM

I noticed something odd yesterday...

72* outside temp, car was managing mid 50s at idle. BUT, the compressor body was cold to the touch. I couldn't find my temp gun to get an accurate measurement, but it felt colder than the suction line.

Does that mean the system is still overcharged?

-J

BrianCostello · #27 06-06-2013, 02:47 PM

Quote:

Originally Posted by compu_85

I noticed something odd yesterday...

72* outside temp, car was managing mid 50s at idle. BUT, the compressor body was cold to the touch. I couldn't find my temp gun to get an accurate measurement, but it felt colder than the suction line.

Does that mean the system is still overcharged?

-J

Those are the same temps that I seem to get. 55-52 at idle, with a small drop to say 47 when moving.

As of right now my car has the "perfect" amount freon. 1.90 lbs (80% of the R12 amount)

I used a proper AC machine. (Kraftwerk in Braintree, MA)

pulled vacuum for 45 min. then let the machine do the work.

As for your compressor temp, I do not know. There are charts showing the outside air temp, and what pressures you should have. It sounds like you have gauges.

Did you ever vacuum the system? I did not at first (just put freon in from the auto store) and it worked, but she works much better now.

General question:

there are various fellows who claim "I get 40 degrees all day, even with 134a" is that moving at 60mph? or standing still at idle. and is it in a W124/126 car?

compu_85 · #28 06-06-2013, 03:06 PM

Yes I vacuumed for 2 hours before filling in the gas. Gauge pressures seem okish (at idle the high side is below 200 and low side is in the high 40s).

-J

compu_85 · #29 06-02-2014, 09:16 PM

So I decided to dump the URO expansion valve I put in last year as I was never happy with the cooling. New OEM part installed, new Hella R/D, flushed the lines to get rid of the green goo from the EnviroSafe. Put it back together, and put on my small vacuum pump.

I noticed movement inside the sight glass, I assumed this was moisture being pulled out of the oil or perhaps some solvent that I wasn't able to get blown out of the evaporator. I left the vacuum pump running when I went to work. When I came home the movement / bubbles were still there. Vacuum would bleed down somewhat quickly. I put in some gas as a test and listened for leaks.

I heard a hissing at the TX valve and with some soapy water found a leak on the suction line going back to the compressor

Have I ruined my dryer by leaving it on the pump all day?

Hooray, I get to do this a 3rd time

Thanks...

-J