OK, here's something I have been researching for a while but have not been able to find an answer for. The A/C on my '97 S420 gets nice and cold with an evap temp of 39-40 *F, but it takes a L O N G time to get there. I'm talking almost 10 minutes when the car runs at highway speed.

My S320 by comparison gets down there very quickly, say 2-3 minutes.

A glance at the A/C diagnostics looks normal to me. Coolant temp stays at around 185, refrigerant pressure sits at 8-10 while on the highway and will climb to 14-15 when going slow or idling.

Anyone ever seen this?

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Perhaps the condenser is a little dirty and needs a good cleanin'.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

Well, I pulled the fans off and gave the condenser a good blowing-out with compressed air. There wasn't a lot of gunk in there and the AC works pretty much the same as before.

I don't know, maybe I'm just being paranoid because of the cost of W140 AC repair.

I did a little more scientific measurement today: With an outside ambient temp of 90-95 *F, and driving at 60+ mph most of the time, it took about 15 minutes to cool all the way down. Once it finally cooled off, the evaporator temp swung between 37 and 41 as the compressor cycled.

Could this be a sign that the evaporator has been changed to an all copper model?

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

See if the RECIRC door is closing all the way....a partially open door will make it hard on a good system to pull interior temp' down.


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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Ditto. My '92 300E uses two dual diaphragm vacuum valves to command either 80% or 100% recirc air. Right now, one or both of my valves has a leak on the 100% side. Therefore, I only get 80% recirc air no matter what until I replace the guilty valve/valves. Until then, anytime the temp is above about 88 degrees, it takes a LONG time for my car to cool down. You need to see how your recirc system is set up for your car.

On your 300E Gilles......if you remove the lower windshield cover...do what I did.

I don't smoke or have anyone in the car smoke.

I pulled the RECIRC flap all the way closed. You first have to screw in a screw through the flap so you can hold the door flap closed with Vise Grips on the screw....Using some self tapping screws with large repair washers, I drilled into the flap near the edge so the washers caught the side of the box holding the RECIRC door shut.

Now it chills like a meat locker ! Only problem was, misting on the outside of windshield as it got cold, so I blocked the upper vents with a length of black tubing.

Vent temps at 90 plus ambient within a few minutes, 39F at medium blower speed.


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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Thanks for your input. However, I plan to remove the dash and replace all the A/C vacuum valves in the near future. After 145,000 miles and an age of 16 years, it's time for a little maintenance on my '92 300E. This involves removing the dash, but I did it before on my '89 300E. After about 4-5 hours, I had the job finished and the system functioning properly. Thanks again.

Thought I'd resurrect this thread and let you know the fix....

The problem kept getting slowly worse until finally the A/C unit logged a fault code. EB1 419 - compressor clutch. I did a continuity check on the clutch and it was fine, so I got to thinking about what else it might be and then it hit me: Last year I put in a cheap, Chinese-made, knock-off fan clutch which proceeded to leak silicone fluid about a month after I installed it. This sticky goo was flung all over the front of the engine bay by the fan blades. So, I put 2 and 2 together and figured that some of this stuff got between the mating surfaces on the compressor clutch which caused it to start slipping. I took a can of brake parts cleaner and hosed it down real good, then after it dried off, I took another can and hosed it down again. Then I took it out for a drive and PRESTO!! It's like I have a brand new A/C system. The evaporator chills down to temp in less than two minutes and stays nice and cold even when I'm sitting at idle or in stop & go traffic.


BTW, I now have a genuine Sachs fan clutch installed. No more knock-off parts for me!

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

I'm very surprised at this cure. If the clutch were slipping, I would have thought that the compressor rotational sensor would have tripped out the a/c altogether. That said, with the later model cars, I believe that the rotational sensor is dealt with in a different way, which if so, would explain this. The newer cars have much "smarter" ACC systems.

The '97 lacks a compressor speed sensor. It uses a thermal fuse in the clutch, which blows if the belt or clutch slips too much. Once blown, you need a new clutch coil at the least, but the FSM says to replace the compressor because it is unlikely that anything other than internal damage caused the fuse to blow.

With some lubricant in there, the clutch would slip without even getting very hot.

I hate the OEM sachs clutches, because for the M120 they only come in one temp setting, and they don't engage until around 100c. I bought one of those aftermarket clutches even though the original was fine, because I wanted to lower the temps. I installed a 71c t-stat, the cool harness mod, and the aftermarket clutch that engages sooner, and now the car is pegged at around 80c, right where I want it.

I hope my clutch lasts longer than yours.