AC Compressor not running until engine cools - upper wiring harness or refrigerant press switch or something else?

[Jlaa]

I "fixed" my air-conditioning and I don't understand the theory behind it!

Sooo ..... ever since I got this car, the air conditioning has been great. With just under 66K miles, the air blows very very cold. Further, I have been using the aircon very sparingly ---- so much better to extend the life of the evaporator so that I can avoid taking apart the whole friggin' dashboard just to replace the the evaporator donchaknow.......

The mediterranean climate here in San Francisco helps too ---- aircon is not really needed.

So today I was in Vallejo, which is perhaps 30-40 miles out of SF --- HOT. And I was going to drop by Robert Fenton's in Marin --- also HOT.

And much to my chagrin, aircon did no conditioning of any sort today. It blew ambient air temps. Sweating....sweating..... I just replaced the thermal paste on the bottom of the EZL this past weekend, and *this* is how you repay me?!?!?!?!

:x

This was particularly baffling because just last week, the aircon was super cold. Today, the aircon was not cold at all --- as if the compressor wasn't doing anything at all. I did detect some strange behavior upon cold-start of the car earlier today --- right on cold start, the electric auxiliary fans were running in low. I don't know why ......

I will note that my aspirator air sampling motor for the air sampling vent next to the sunroof switch seems not to be able to pass the tissue paper sucking test ...... but even then, when cycling the temp control to max cold, the air that comes out SHOULD be conditioned right?

• temp control - max cold ---> result is ambient air temp
• temp control - max hot ---> result is hot air
• temp control - between max cold and max hot ---> result is ambient air or hotter air

So I took the car home instead of dropping my Robert Fenton's (argh) and read a bajllion AC threads on 500eboard. And then I went into the garage and read the codes.

Pin 4 - LH-SFI --- all okay

Pin 6 - ABS/ASR ---
+ Code 21 - ABS/ASR Hydraulic Unit Pressure Switch Charge
+ Code 22 - ABS/ASR Hydraulic Unit Pressure Switch Leakage
+ Code 30 - CAN Data Bus to Control Module Interrupted

Pin 7 - Electronic Accelerator / CC / ISC
+ Code 6 - Starter Lockout / Backup Lamp Switch
+ Code 14 - Closed Throttle Position Switch

Pin 8 - Base Module
+ Code 5 - Max Allowable Temp in Module Box Exceeded

Pin 16 - Auto Climate Control --- all okay

To be fair, I don't remember if I've ever cleared any of these codes before, with the exception of any codes for the LH-SFI computer which I did clear when I swapped in the '92 LH computer. Some of those codes may have been there for God-knows how many years.

Anyways, I cleared all the codes. Then, I replaced all four 10-amp fuses in the main base module box --- even though the fuses did look fine. I'll note that one of the fuses looked like it had been replaced before.

Then I started up the car --- and wouldn't you know it, the AC worked just fine.

Anyone run into this before?

 

[Melville]

Re: Why oh why is my air konditioning no longer kaput ?!?!

It has been my experience that MB engineered their cars so that they occasionally experience failures such that, after all attempts to repair have been exhausted, all hope is lost. Just then, without explanation, they miraculously fix themselves. This is so that we do not grow complacent or lose respect for the machine. Instead, we remain in awe of their magnificent powers.

GSXR or Klink may have a different explanation, but I'm pretty sure I'm right.

 

[TerryA]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Sounds like one of the fuses was NOT fine. Probably a little corrosion in the connection.

 

[doolar]

Re: Why oh why is my air konditioning no longer kaput ?!?!

All I can say is - use the aircon, all the time. The system needs to work to be able to lubricate all sealings. When not in use, that's when they start leaking. Always the same problem here in Sweden, people turn the compressor off during the winter time, when spring arrives, no cold. Every single aircon technician I've ever met says the same thing - let it be turned on all year. I've done this since forever, and very rarely see a problem with the aircon in any of my cars.

My Toyota econobox is 14 years old, has around 175.000 miles on the clock, is driven all year through salt, rain, snow, winter and summer. I serviced the aircon this spring, it had lost about 10% medium over the last six years since I serviced it, which is very acceptable. Use the aircon!

 

[8899]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Further, I have been using the aircon very sparingly ---- so much better to extend the life of the evaporator so that I can avoid taking apart the whole friggin' dashboard just to replace the the evaporator donchaknow.......

I agree with Doolar...not using your aircon probably does more harm than good. I never use the "EC" function because I want the aircon working all the time.

 

[alexis]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Hi,
I use my AC all the time in summer but rarely in winter. That said, in winter, I use it every two weeks for about 10 minutes at least to lubricate the sealings and the compressor.
I have done that since the beginning and the system blows ice cold air all the time. Quite impressive, especially considering the fact that I haven't filled in the system for more than 14 years ! Yes, that long...
If I had to resume Mercedes reliability, I think I would use that example to illustrate it.

 

[Jlaa]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Maybe my air conditioning is not working properly after all.

I took my car for a drive from a cold start. For the first 10 minutes of city driving everything was fine and the air conditioning worked great. After 10 minutes, I noticed that the electric fans had kicked in. Shortly thereafter (less than 90 seconds) I realized that the AC compressor was no longer operating and that the air coming out of the vents was not conditioned.

I drove another 60 minutes in speeds varying from 5 mph bumper-to-bumper traffic to 75 mph on the freeway. At no point did the air con come back ... although I did notice that the electric fans, on about 15 occasions, would shut off for 1/2 a second or so and then immediately come back on.

Then I parked the car. The car cooled off for 2 hours. My father hit the car the car with his own car (long story, argh). Then I drove the car again. For the first 5 minutes of city driving, the air conditioning worked great .... and then again the AC compressor seemed no longer to be operating and the air coming out the vents was not conditioned. I drove for 45 minutes at freeway speeds and parked the car again.

After letting the car sit for another 90 minutes (buffing out the scrapes in my rear fender to the best of my ability) I started the car up in my garage ---- and air conditioning worked again for about 3 minutes. The electric fans were NOT on. After about 3 minutes, I realized that the electric fans started to turn on again ..... and I thought that the air conditioning started no longer conditioning the air again ... and I shut the car off.

Any idea what this might be? The ambient temperature was around 72F and at no point did the car's temp gauge exceed 90C.

Could this perhaps be a failed AC pressure switch as noted here? http://www.500eboard.com/forums/showthread.php?t=8632&p=111198&viewfull=1#post111198
Or perhaps could this be a failed evaporator temperature sensor as noted here? http://www.500eboard.com/forums/showthread.php?t=7280&p=91304&viewfull=1#post91304

Or perhaps the problem is way more sinister? Perhaps this is the upper wiring harness needing replacement? Or maybe the electric fans turning on have nothing to do with the AC compressor not running?
The car drives fine --- but see these photos. I don't have a sticker on the big thick cable mass near the CAN box, but I do I have a sticker on the much thinner cable that "merges" with the big thick cable near the CAN box and the F.D. (production date) shows some time in 1993. I remember at one point the seller or the PPI shop telling me the upper harness has been replaced, but now I'm not so sure....




As well, below two photos --- one showing the wires to the ECT sensor and another showing the wires to the driver side camshaft magnet ...





Thanks for any / all advice.

 

[TerryA]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Jlaa,

Have you checked the bar fuse for the electric fans? I once had a similar problem and it was this fuse. It's on the firewall left of the fuse box. If your fans work intermittently it will cause the A/C compressor to shut off sometimes. The fuse connection gets corrosion on it and causes the fans to stop.

It's worth a look.

 

[samiam44]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Bad base module in the CANS cured my problem.

M

 

[gsxr]

Re: Why oh why is my air konditioning no longer kaput ?!?!

If the F.D. (production date) shows some time in 1993, that harness is original. Your photos confirm this - a late-datecode replacement harness would have zero degradation of the insulation. On the bright side the harnesses are still available new, not terribly expensive, and are DIY replaceable in ~1 hour or so.

Dumb question: Can you tell if the electric fans are running on high or low speed, when they do trigger? There are detailed threads on this topic, but the low speed is only triggered by refrigerant pressure (over 16 bar), and the high speed is only triggered by engine temp (over 107°C, unless a CoolHarness has been installed, which I don't see in your photos).

 

[Jlaa]

Re: Why oh why is my air konditioning no longer kaput ?!?!

Jlaa,

Have you checked the bar fuse for the electric fans? I once had a similar problem and it was this fuse. It's on the firewall left of the fuse box. If your fans work intermittently it will cause the A/C compressor to shut off sometimes. The fuse connection gets corrosion on it and causes the fans to stop.

It's worth a look.

thanks - are you referring to the 30 amp strip fuses? I replaced them all w new ones a few months ago. I would say the fans work nearly constantly ---- never stopping ---- punctuated by 1/2 second stoppage one every few minutes.

 

[Jlaa]

Re: Why oh why is my air konditioning no longer kaput ?!?!

If the F.D. (production date) shows some time in 1993, that harness is original. Your photos confirm this - a late-datecode replacement harness would have zero degradation of the insulation. On the bright side the harnesses are still available new, not terribly expensive, and are DIY replaceable in ~1 hour or so.

Dumb question: Can you tell if the electric fans are running on high or low speed, when they do trigger? There are detailed threads on this topic, but the low speed is only triggered by refrigerant pressure (over 16 bar), and the high speed is only triggered by engine temp (over 107°C, unless a CoolHarness has been installed, which I don't see in your photos).

Thx - I ordered a new harness ... $383 from Renee @ Naperville.

I THINK the fans are ALMOST always running on high. I need to confirm this ..... but Im scratching my head ..... fundamentally I tnink I need to figure out if the constant hi running fans are related at all to the ac compressor calling it quits until the engine cools down. The fact that hi speed fans are triggered by coolant temp, not refrigerant press makes it confusing.

Some questions -

- Does the upper wiring harness carry information from any sensor which would stop the AC compressor?

- How can I test the AC press switch shown here? http://www.500eboard.com/forums/showthread.php?t=8632&p=111198&viewfull=1#post111198. Can I short the leads of the switch? What I want to do is to simulate a pefectly working AC press switch while the fans are droning away ....

thanks

 

[gsxr]

Re: Why oh why is my air konditioning no longer kaput ?!?!

I THINK the fans are ALMOST always running on high. I need to confirm this ..... but Im scratching my head ..... fundamentally I tnink I need to figure out if the constant hi running fans are related at all to the ac compressor calling it quits until the engine cools down. The fact that hi speed fans are triggered by coolant temp, not refrigerant press makes it confusing.

First thing would be to confirm if the fans are running on high or low speed. With the AC off, pull the connector off the 2-pin sensor at the front of the intake manifold. This is in your photo, on the right side of the 3 sensors in a row (1-pin is for dash temp gauge, round 4-pin is for the engine fuel+ignition management computers).

Does the upper wiring harness carry information from any sensor which would stop the AC compressor?

I don't think so, but I may be forgetting something.

How can I test the AC press switch shown here? http://www.500eboard.com/forums/showthread.php?t=8632&p=111198&viewfull=1#post111198. Can I short the leads of the switch? What I want to do is to simulate a pefectly working AC press switch while the fans are droning away ....

That is the high/low pressure safety switch, this would prevent the AC compressor from engaging if the refrigerant pressure was to high or too low. You can safely short this out for test purposes, when the compressor is NOT running, to see if the compressor engages. Of course, don't leave it shorted out.

To test the FANS... you would short the leads for the pressure switch right next to the one pictured in the above thread, it will be a red switch with 2 pigtails. When you short those, the electric fans should run on low speed.

 

[Jlaa]

Thanks GSXR - OK here is what I found out. The electrical connection to the 2-pin sensor at the front of the intake manifold is flaky, big time. Post #7, last photo, right most sensor.

- Bone Cold car --- has been sitting over night
- Ignition in on position, but engine not running.
- With the connector removed, the fans run at high speed
- With the connector installed, the fans ALSO run at high speed --- unless I jiggle the connector just so, and then I can get the fans to shut off for a few minutes until the connector "readjusts itself" and then the fans turn on high again.

So I think this definitely means time for a new upper wiring harness.....

Now --- are the hi speed fans or the 2-pin temp sensor somehow related to the AC compressor not turning on? This is what happens ---

- Bone cold car, hi speed aux fans running (because of faulty electrical connection on the 2-pin sensor)
- Start car --- NO AC ---- shut car off after 1 minute

- Fairly cold cold, hi speed aux fans not running (because I maneuvered the 2-pin sensor connector *just* so)
- Start car --- PLENTY OF COLD AC ---

This is baffling to me ..... why is AC compressor activation and this 2-pin sensor related?

Some additional clues ---- I pulled all the codes --- no codes on anything except 2 codes on Pin #19 which I tried clearing multiple times to no avail -

#6 - Idle speed control inoperative --> (note the guide says then to test the electronic accel --- but there are no codes)
#9 - intake air temp sensor - open/short ckt --> (note the guide then says to test LH-SFI --- but there are no codes)

?? Related at all?

Thanks

 

[gsxr]

It is possible that if the 2-pin temp sensor (affected by the upper harness) is telling the HVAC pushbutton unit that the engine is overheating, that this is triggering a safety by disabling the compressor. I've not encountered this failure personally so I'm not certain, but I think you might be on to something here! Especially if the compressor always works when the fans are NOT running on high speed.

Codes on pin 19 (DM) will not completely go away until after the engine is started. The IAT sensor is behind the driver headlight, plugged into the plastic 'bucket' where the air tube connects. If you had unplugged that for better access to the AC switches and had the ignition on, this could have caused code #9. Just make sure the sensor is plugged in. This wouldn't affect the AC compressor though.