A/C Recharge Question- Help? - PeachParts Mercedes-Benz Forum

#1 06-07-2004, 10:06 AM

My 79 280CE had already been R-134 converted when I bought it, and needed only a home recharge, then worked fine last summer. Just now getting hot in Minnesota (and really hot & humid this week), I attempted a recharge yesterday with no success. I "think" my problem is that the compressor won't run if there isn't enough refregerent in the system, and so it wouldn't suck the replacement 134 in. If I'm right, how do I bypass whatever compressor shutoff there is and so recharge? Or is my logic faulty?

ctaylor738 · #2 06-07-2004, 10:36 AM

Pull the connector off the dryer bottle and bridge the contacts with an alligator clip or piece of wire.

#3 06-07-2004, 10:42 AM

Thanks Chuck, as always. But pardon my ignorance. "dryer bottle?" Vas ist das? My knowledge is limited to pointing at the big York compressor, knowing where to attach the A/C fill hose, and that theres a little unit in the lower left of the engine compartment with a glass window to look for freon bubbles.

ctaylor738 · #4 06-07-2004, 10:46 AM

"little unit in the lower left of the engine compartment with a glass window to look for freon bubbles"

That would be the dryer bottle. There should be a two- prong connection on top of it.

WANT '71 280SEL · #5 06-08-2004, 12:13 AM

When you connect the refrigerant hose the compressor will come on as it gets pressure forced to it. The compressor should come one by itself after the hoses ar connected etc because the pressure will flip the switch.
Thanks
David

#6 06-08-2004, 10:09 AM

Quote:

Originally posted by WANT '71 280SEL
When you connect the refrigerant hose the compressor will come on as it gets pressure forced to it. The compressor should come one by itself after the hoses ar connected etc because the pressure will flip the switch.
Thanks
David

Thats what I thought might happen. It didn't. I got the sense there was more pressure in the system than in the can. (I even attempted to bleed some pressure off by poking a probe into the high side discharge...just air, and a spritz of freon came out.) So the original question. And Chuck's suggestion didn't work. The compressor fan belt is turning constantly, which I think is correct and there's some type of internal clutch that needs to engage, but no 134 is going in. I pulled the two wires off the dryer as Chuck advised and bridged the two male prongs on the dryer. No change. Ok, maybe I was doing it backwards, so I put the wire into the female spade connections and bridged the two wires. No change. I was using a doubled piece of speaker wire for the bridge, and I suppose it is possible I didn't establish a good connection (It was 96 degrees and humid and under the hood, it was too hot to work for more than a few seconds before having to back out and wipe the sweat out of my eyes). What am I doing wrong? I was able to re-charge with no problem last summer and again in Sept. (so I know there's a leak) Help?

ctaylor738 · #7 06-08-2004, 10:22 AM

If you used the Defrost setting on the panel, and if you have the pressure leads jumped, the clutch on the compressor should engage.

If you try this with KOEO, you should hear a click from the clutch. If you don't, test the lead to the compressor for 12V. If you have 12V and no clutch engagement, then you have a bad clutch.

If you do not have power on the lead, then you need to work your way back through the relay to the pushbutton to the fuse to find the problem.

These early ACC systems can be a bear to troubleshoot.

#8 06-08-2004, 11:25 AM

Quote:

Originally posted by ctaylor738
If you used the Defrost setting on the panel, and if you have the pressure leads jumped, the clutch on the compressor should engage.

If you try this with KOEO, you should hear a click from the clutch. If you don't, test the lead to the compressor for 12V. If you have 12V and no clutch engagement, then you have a bad clutch.

I didn't use the defrost setting, just the high heater/ac button. Am I reading this that I should be bridging the two wires and not bridging the male prongs on the dryer?

Whats KOEO?

ctaylor738 · #9 06-08-2004, 11:34 AM

You should bridge the wires, not the prongs on the dryer. I use a piece of #14 house wire but whatever you use should be equal to the wiring to the switch.

KOEO = Key On Engine Off

#10 06-08-2004, 11:41 AM

Gotcha. Will try again tonite

#11 06-08-2004, 03:08 PM

Your sure that the system needs freon? You may have it full and just have a bad clutch.
Thanks
Tim

#12 06-09-2004, 11:44 AM

Quote:

Originally posted by Tim's__Benz
Your sure that the system needs freon? You may have it full and just have a bad clutch.
Thanks
Tim

"Just" a bad clutch isn't an encouraging thought. I got sidetracked and haven't done the "click" check test yet, but it cooled off here and the car is sitting home today waiting for a fellow to show ( I hope) who is installing new upper control arms for me cheaply. And I need to make a hardware store run for a couple of spade connectors to insure my dryer bypass bridge will be a good connection....I've misplaced the one I made to bypass the electric fan cut off for really hot days and no longer needed with the now replaced radiator. I also got a post on the tech board that the old York compressor just can't handle R-134 pressure, suggesting a retrofit to R-12...hmmm, not a preferred solution either. I really like driving this car, but I told my wife that if the A/c problem became spendy, it is the final straw. Odds are, I'll park it, buy another driver and put the car up for sale.

ctaylor738 · #13 06-09-2004, 12:52 PM

Not true about the York.

My 280C was converted by the Previous Owner in 2000. I have not had to touch it since I've owned it, and it still blows very cold. If you have a marginal compressor, though, the R134 might hasten its demise.

R12 will give you better cooling, and supplies are not as tight as they were in previous years. So if you have to replace a major component, it might not be a bad idea to convert back.

psfred · #14 06-09-2004, 07:25 PM

You only need to touch the wires together off the connectors -- it's a pressure switch, closed when there is adequate low side pressure, open if not.

Find the wire to the compressor clutch and jumper it to the positive side of the battery with a piece of wire. Should go click (rather loudly with the engine off). If not, it's either out of adjustment or bad. You can check resistance with an ohmmeter from the wire to ground.

Do not attempt to charge the system without the engine running, you wound get anything in there unless there is suction on the cold side. Never, ever, attempt to charge the high side with the engine running, the can can explode, and this will seriously injure you.

You really need a set of gauges for this, they are about $50 most of the time.

The York compressor is wonderful. The only reason they are not still in use is the combination of size, noise, and vibration. The will handle 134A just fine, and even cool rather well. You can easily drain and refill them with the correct oil, too, with the system empty!

Peter

DANTRCAV · #15 06-10-2004, 08:12 AM

Peter is correct. York compressors are fine. I have converted 4 systems with Yorkies. They are still available NEW. I put a new York on my 250 when I did that and it cost $135.00.

It has been my experience that if you have too much charge in a York that it will "growl" and sound like it is running on square bearings!! You really do need gauges to do this correctly. At least you might want to pick up a single gauge with a short hose that connects to the low side (at a minimum). Some come with adaptors for high side. I have seen them for about $20.00 at PepBoys and AutoZone. There is also a combo unit ($20.00 I think) that doubles as a fill and gauge with a pistol grip that works off the low side. If you keep your low side pressures under 50psi you will be fine - 45psi is what I normally charge to.

DO NOT attempt to charge with R134a until the sight glass is clear - you will have way too much charge.

If you jump the comprssor from battery + and the clutch does not engage and the fuse is good then you "probably" have a bad switch. My 250 and my friends 280 both had bad switches. On both, the capillary tube that runs from the switch to the evaporator (this controls temp and is supposed to keep the evap from freezing) was broken at the switch and that did not allow current to flow to the compressor.

One more thing, as many of these as I work on I still sometimes forget. Make sure that the low side (charging) port valve is turned in (clockwise) about two turns or nothing flows!! That valve is normally "back seated" or all the way out (counter clock-wise). I did this two weeks ago working on my Jeep - just got in a hurry - sure felt silly!!

Good luck.

Dan