A 300E compressor might be a direct replacement.

If you can live with an ice cube relay, you might be able to get away with a compressor that doesn't have the requisite MB speed sensor.

One of the lower pressure switch contacts gets +12V from the PBU to engage the compressor. Set the PBU on defrost with the engine running and check for +12V from one of the wires.

Sixto
87 300D

Well, here's the current situation:

1) I jumped from the battery straight to the compressor, and got it to turn on. The air blowing into the cabin was cold... for a few seconds, then it was just air after that. So, at least the compressor will turn on. No nasty noises or anything, actually completely silent.
2) The system has already been thoroughly converted to r134a. Based on discussions on other threads, it seems like my best best right now would be to use Duracool or ES-12a, since either of those would cool better than r134a (which many people have said just WILL NOT COOL in a w124). It would seem to be silly to pay all that money to convert the system again BACK to R12, after paying to switch it to r134a. Especially since I don't live in a particularly hot area... I just want the system to blow cold when I'm driving through hot areas on the way to someplace else. 38-degree vent temps at 95 degrees at highway speeds is my goal. I'll settle for 42 degrees @ 95-degree ambient, though. ;-)
3) I now have a new multimeter and soldering iron on order, which should allow me to start trying to track down & fix any electrical gremlins in the system.
4) My next step is to evac the system, fill it with vacuum, and see how long it holds a vacuum. Then, if it does not hold a vacuum, give it the nitrogen test to see where the leak might be (not sure if I'll be able to source the R-22 for that... think it'll be fine to not use R-22 for the nitrogen test?)


Any thoughts?

Thanks for the help so far! I might want the name of that shop in San Rafael later, depending on the outcome of my upcoming tests... ;-)

cheers,
~Garlynn

hello. I've just had the Compressor, Expansion Valve and Drier done.
I got the parts from Polar Bear in Ft Lauderdale $300 dollars for the parts. (Speak to Gretchen) The compressor rebuilt was mine. They didn't have a core in stock. Quick turn around.
I'm in central Fla and getting approx 30 degree cooling drop using 134A.
The wife is happy so I'm happy.

__________________
92 300D 2.5L OM602 OBK #59

I would just use R134a, especially considering that you live in the bay area.

I conducted a small experiment when I rebuilt the system in my 1987 300TD. I replaced everything - evap, condenser, compressor - all at once. I used a universal synthetic a/c oil that works with both R134a and R12. Just for grins I charged it with 134a and drove it around Dallas. In July. You know what - it was fine. I did eventually change it to R-12, mostly because I had the refrigerant and was curious what the difference would be. It's been a couple of years since then, and my memory has blurred. I think the final vent temperature was the same for both refrigerants. Subjectively the R-12 cooled down faster - the air was chilly by the time I backed out of the driveway. With R-134 that didn't happen until a few hundred feet of driving.

I posted up these results in an old thread, probably still in the archives. Summer of 2004, I think. I'm too lazy to search for it...

- JimY

Jim- Well, that's a good point of information. It seemed that on a previous thread, pretty much everybody cam to agreement that R-12a/ES-12a were vastly superior to r134a, but more or less roughly equal to R12, depending on what you placed the most value on (engine efficiency or cooling ability at idle).

Also, a lot of folks have commented that the w124s just won't chill properly with r134a. Interesting that yours will! I still need to conduct more tests on mine... I'm on the fence between replacing a lot more of the system like you did, vs. just getting the electrical part working again, checking/fixing leaks, and re-charging.

I'm primarily not fixing the A/C for use within the Bay Area. I do a lot of driving between SF and Oregon, which means going through the 110-degree Sacramento Valley. THAT'S where I need the A/C, and I need it to work COLD (i.e. 50-degree difference, ideally).

I'm perfectly happy with the cooling in my '87 w/ 134a.

__________________

Gone to the dark side

- Jeff

That'd be something

Sixto
87 300D

Touche... I guess I meant to say, "draw a vacuum." ;-)

I was hurried and omitted a few thoughts during my last post. We've had a theory around the old forum that decreased cooling in older cars was due to degraded/clogged condenser and evaporator more than R-12 to R-134a conversion. Part of my test was intended to validate or reject that theory.

Both the evap and conderser are radiators. The function of the evaporator is to transfer heat from the air stream (inside the car) to the refrigerant. The function of the condenser is to transfer heat from the refrigerant to the air stream outside the car. The more the fins on each are bent, coated with dust, and blocked by leaves and other detritus, the less heat transfer occurs.

These older cars don't have filters for the HVAC system. If you dig into some old threads there are pictures of a 20 year old, 200K mile evap. Crudded up is a mild description.

Anyway, I expect that R134a would work fine for driving through the valley at highway speeds. To be comfortable in that kind of temperature it's necessary to insure the recirculate function works properly. You won't be cool if the car is drawing in outside air, there's just not enough cooling capacity to drop 110 degree air. You need to run 100% recirc. I'm also a fan of good window tint - it really reduces the heat load. I always have my wagons tinted with Llumar metallic film, it does a very nice job of rejecting the radiant heat of the sun.

- JimY

So, the new multi-meter (and soldering iron) arrived, and today I went to work to try and figure out what's going on with Eleanor's A/C (1987 300TD). I used an old checklist off this forum. Let me just go through it briefly:

1. Turn Car off
Response: Already off.
2. Pull Klima Relay Out
R: As noted previously, KLIMA is missing already. "Ice Cube"-type device exists instead.
3. Put your multimeter on DV Volts setting
R: Confirmed setting by testing across both terminals of the battery, drawing about 12.6v.
4. Connect the ground terminal of the meter (black color usually ) to the battery's negative terminal
R: done
5. Connect the positive terminal of the meter to pin number 5 in the socket.
R: Located, done.
6. You should get close to 12V.
R: The author of the instructions forgot "turn on car at this point." After turning on car, 12V is measured.
7. If 12V measured and compressor clutch still does not run, move on.
R: Compressor clutch does not engage.
8. Remove KLIMA. Connect negative terminal of meter to pin #10 and positive terminal on positive battery terminal.
R: done
9. Turn on the car and press one of the a/c switches on the push button unit.
R: done
10. You should get close to 12V when the a/c switch is on
R: negative -- no voltage.
11. If you don't get close to 12V then there are one of two possibilities:
a. the push button unit is not sending the correct control signal
b. the pressure switch is not closed
(ignoring possibility of broken wires or connectors)
12. Turn the car off.
R: done
13. If you don't get the 12V, disconnect the two cables from the pressure sensor and jumper them.
R: Which two cables, again? The ones on top of the sensor, or the ones about halfway down the two wires leading away from the sensor? Tried both.
14. Repeat steps 9 & 10:
R: Negative -- no voltage, jumping either of the sets of wires.
15. If you still don't get the 12V, the push-button unit is not sending the signal.
R: I refuse to believe this, as the push-button unit was brand-new and installed in July, 2007. Is there any other test to confirm or deny function of the push-button unit, or to troubleshoot any possible electrical gremlins between it and the KLIMA?

At this point, I had to stop trouble-shooting, because of the obvious impasse -- the electrical gremlin appears to be somewhere between the push-button unit and the KLIMA, but where, and how to check?

Any advice would be MUCH appreciated.

thanks!

cheers,
~Garlynn

P.S. Just for fun, I did some tests on Gladys, the 1982 300D. When her pressure switch is jumpered, the compressor switches right on, no problem. She is still plumbed for R12, but appears to have next to no charge left. Am considering evacuating her system, drawing a vacuum, and checking for leaks, then locating them with nitrogen if they exist. Just need to figure out a way to string an extension cord out to the cars, since the evacuation pump draws about 1,000 watts (too much for the inverter). Am thinking it would be easier to get the A/C going on the w123 than on the w124, but really would like to have it going on both!!!

Did the A/C ever work with this pushbutton unit?

I'm tempted to send you my spare CCU/pushbutton unit for a test, but if yours is toast, the same problem might toast mine. A lower-risk trial would be to find someone with an '87 300D/300TD near you who will install your CCU in their car to see if it works properly.

__________________

Gone to the dark side

- Jeff

Well, the A/C supposedly worked last summer, after the shop installed the new CCU, converted to r134a, did some other work and recharged it. At the time, however, I wasn't familiar enough with the A/C to visually verify that the compressor was turning on when the CCU was supposed to be activating it... but for lack of any other information, I must assume that was the case, as the shop did state that it was blowing at 56 degrees cold.

Is there a way to test for the problem that you indicate that could potentially "toast" a CCU? Continuity in a circuit, or something?

thanks,
~Garlynn

9. Best to set it to defrost so the cabin temp sensor is out of the equation.

11. Don't forget the evaporator temp sensor.

12. Some cars (pre-90?) have a time delay Klima relay. The Klima won't engage the compressor for ~10 seconds after starting the engine or something like that. Later Klima relays don't have the delay.

13. It's the switch with 2 contacts. The switch 2 pigtails is for the aux fan.

If you can figure out which low pressure switch wire goes to the Klima, force +12V into the wire and see if the compressor engages (keep the other wire disconnected). You can tap +12V from the glow relay strip fuse.

Sixto
87 300D

Sixto-

9. -- Good advice, I'll make sure I only use that setting when performing these tests. I think it is what I have been using all along.

11. Where is the evap. temp. sensor, and what am I looking for with regards to it?

12. I've noticed that it does take about ten seconds from ignition to fan activation, though as noted, Eleanor has no KLIMA -- she has the "ice cube" or equivalent. Is the delay built into the KLIMA unit, or is it elsewhere in the system?

13. OK, got it -- pigtails = aux fan, spades on unit = compressor.

...and now, for the results of the test of forcing +12v into the wire from the pressure switch to the KLIMA:

It does not engage the compressor.

However, I did detect +12v when doing so, using a multimeter with the + pin in the + node of the battery, and the - pin inside socket #10 on the KLIMA socket.

So, knowing that the "ice cube" is a complete unknown (i.e., I suspect that it is non-operational), I decided to jumper socket #10 to (double-checking the wiring diagram at 83.606 p. 43) socket 7, heading to the compressor.

When this jumper is performed, the compressor turns on (again, power is still coming from the glow plug strip fuse to the pressure sensor plug headed to the KLIMA).

What does that tell us?

* The "ice cube" thingy is probably non-operational?

* What else?

Thanks!

cheers,
~Garlynn

Here's something to try. The gas and diesel 124 models use different part numbers for the CCU pushbutton unit. The diesel sends ground to pin 10 of the Klima socket to signal for compressor activation. This is what you were testing in step #8 above. The gas version sends +12v to signal compressor activation. On the off chance the pushbutton unit was replaced with an incorrect part number, I would check for +12v at pin 10.

The evaporator temperature sensor is a thermistor - a resistor whose resitance varies with temperature. It is used to measure the temperature of the chilled air flowing off the evaporator. If the air becomes too cool, indicating a risk of ice forming on the evaporator, then the CCU will shut off the compressor until the temperature rises. Evap temp sensors do occasionally fail, resulting in intermittent or non-operational a/c - the CCU thinks the evap is too cold to permit running the compressor. Checking the sensor is easy. Remove the CCU and measure the resistance of the sensor with your new DVM. There are two wiring connectors to the CCU, each with a dozen or more pins. Unfortunately, I do not have handy the information on which pins to measure, nor the expected resistance values. That information may be the archives. I can post it later if necessary.

- JimY