W123 new AC system q's - PeachParts Mercedes-Benz Forum

dcraigk · #1 06-05-2017, 11:18 AM

I had a new compressor, expansion valve and receiver/dryer installed on Friday and I'm not sure it's working properly.

When first starting the car I need to increase the idle speed to 2000+ for the compressor to kick on.

If I start and drive, the compressor kicks on after a couple hundred feet of driving. I can feel it kick on because the rpm's change and there is less power.

The cooling seems to stop at a traffic light. But I think the compressor is still engaged.

I wasn't sure if the aux fan was working but it did come on last night when I pulled into the garage. I sat and let the car idle for a few minutes expecting it to shut off and it never did. The engine temp was normal.

I've read different opinions about R134 from not-so-good to great so I'm not sure if this is normal behavior or maybe it's still low on R134. Thanks

Diseasel300 · #2 06-05-2017, 12:01 PM

Before getting carried away, make sure the electrical portion of your system is working properly. You shouldn't have to rev the engine for the compressor to kick on. Since you have a 1985 model, you could have Klima relay problems or issues with the Tach signal.

When you did the work, you DID pump the system down into a deep vacuum to boil off any moisture right? If not, you will need to do so or the system will never work properly.

R134A is far less efficient at heat transfer than R12. The A/C system in the W123 was marginal when new and will be less than spectacular with a conversion. Charge by weight and use 80% of what the system calls for in R12.

Make sure you installed PAG or POE oil in your system. Mineral oil is not compatible with R134A.

Additionally, airflow is your friend. Take degreaser and clean out your condenser and radiator and blast it out with a good hose (don't bend the fins!!!). Make sure your engine driven fan is in good working condition. If the clutch isn't engaging when hot, you're losing a huge amount of airflow through the condenser.

dcraigk · #3 06-05-2017, 12:30 PM

I didn't do the work, I had a mechanic/AC guy do it. The parts came from Napa. It's sold as a kit with a new compressor, rec/dryer, expansion valve and a small bottle of clear oil. I think it said PAG.

When I went to pick it up he said he could only get the compressor to come on by jumping it. I told him about the Klima relay. He pulled it and put it in slightly and could feel it clicking. I took the car home, jumped the Klima sockets and heard the compressor engage. I put the Klima back in and this is where I am now.

I am having tach issues. Currently I have the ECU removed and the tach wires jumped. I have a tach now. I thought maybe this is making the AC not work right. I ordered another ECU because the first one I bought didn't work. It should be here tomorrow. Hopefully this one will work.

I'll ask about the deep vacuum. The fins look good but I'll clean them. The engine fan clutch seems to be engaging.

I'll get a reading from my vents and post back.

dcraigk · #4 06-05-2017, 12:37 PM

Is the Klima just for the AC? The reason I ask is someone on eBay is calling it a Kickdown/AC relay and I don't really have any kick-down. Rarely it works.

Diseasel300 · #5 06-05-2017, 02:33 PM

The Klima relay also controls transmission kickdown. Not sure why the two are incorporated into one relay, but they are.

dcraigk · #6 06-05-2017, 02:38 PM

Ahh well that may be why I don't have kickdown.

Diseasel300 · #7 06-05-2017, 02:40 PM

If your Tach signal is screwed up, the Klima relay may be fine. Both the kickdown and A/C compressor are RPM based. If the signal isn't present at the Klima relay, don't expect either to work properly.

dcraigk · #8 06-05-2017, 03:15 PM

I jumped the ECU tach wires, so my tach is working. I guess I need to get the ECU working correctly first and see what kind of changes I get.

Diseasel300 · #9 06-05-2017, 07:09 PM

I can't say with certainty whether or not the jumpered ECU pins would result in a working Klima or not. I'd expect the ECU to amplify the signal in some regard and the Klima relay may be expecting that signal which obviously won't be present if the ECU is not in place and working.

Volvo Diesel · #10 06-05-2017, 08:23 PM

I have the same car, and on my vehicle there is a separate relay on top of the valve cover that cuts off the A/C compressor once the throttle is depressed sufficiently. It has nothing to do with the transmission "kicking down," although people frequently think that's what it does. Now it may be the relay on the valve cover sends a signal to the actual KLIMA relay to shut off the A/C, but there are 2 relays. I have had issues with the relay on top of the valve cover before causing intermittent problems with the compressor operating properly.

Sadly, there are not that many mechanics around that know the A/C systems well in these cars, and having the CA version with the KLIMA relay adds yet another layer of complexity. Many of them just want to add freon and send you on your way. The system will never work amazingly well with R134A, but it should certainly work better than you describe. I daily drive mine in Austin, TX, where the summers get hot and humid, and mine keeps me more or less comfortable. Perhaps the "good repair shops" forum will have info on a place in your area to take it to be diagnosed?

Good luck,
Chris

dcraigk · #11 06-05-2017, 08:36 PM

Yes I know about the switch on the valve cover because when I pulled on the 'Stop' linkage to simulate full throttle, the little plastic bump didn't reach the switch to activate it. A week later I realized it didn't reach because my pivot bushing on the firewall had disintegrated. A new pivot bushing and it now will trip the switch, but I don't know if the switch works.

First things first is to fix the EGR computer. That thing does more than just the EGR and it should be functional. Once it's working, next will be to test the KLIMA. Again, that thing does more than people realize. I thought it was just for the AC until today. Now I know it controls the transmission kick-down too. Occasionally I get the transmission to kick-down but it's only done it a few times and has never kicked-down with the switch under the pedal.

vollpreuss · #12 06-05-2017, 08:39 PM

Here's all sorts of reading on the Klima relay and the EGR computer for the 85 Cali. Based on the second link the EGR computer strikes me as a pass through.

http://www.peachparts.com/shopforum/diesel-discussion/359300-ac-compressor-wont-come-85-300d.html

http://www.peachparts.com/shopforum/diesel-discussion/341652-quick-fix-1985-w123-tach-c-after-egr-failure-3.html