Well, about a month ago, I noticed the air in my '88 300E to not be cooling very well. This worried me, afraid of the infamous evaporator problem. I had never had to add refrigerant, so I just hoped that it was a tiny leak that had lost the refrigerant over the period of many years.

I charged the system, probably added a little more than a pound. I drove the car and got vent temps below 40 degrees. I was VERY satisfied, and wishing for a sweater. I also put in UV dye at that time.

I had not driven the car until a few days ago and then drove it to find that the vent temp is only getting down to about 52, best case. I worried that I had a bad leak and got out the black light. I went over it THOROUGHLY and could find no leak anywhere. Today, I put the gauges on to see where I stood. I STILL had the same pressures I had when I charged it. It is making condensation drain like Niagra Falls so I am convinced that the refrigeration portin is working well.

This means that either a flap under the dash is not working properly or the climate control is calling for coolant. Possibly the heater valve could be seeping a little coolant through I suppose.

Well, anyway, I have been SOOOOooooo lucky with this car to have never had to do anything to the a/c. I am really glad that I have no bad leak.

Are any of you intimately familiar with the climate control et al? Can you suggest anything? The temp sensor blower is working. The blower motor is blowing well and all the vents are putting out cold air, it's just that the air is not as cold as it should be.

BTW. My pressures are: 28 low, 275 high, about 52 or 54 vent temp.

Thanks,

What was the ambient air temp Larry? If you are getting 45-50 degrees cooler than ambient, everything is working correct, as I understand the system.

Just shadetree refridgeration talking.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

What is the sight glass showing ??

Ambient was about 90. I have kept a dial thermometer in the vent for the last few years. In the past the vent temp would be right at 40, even if it was 110 outside.

Sight glass is clear and pressures are on the money. The problem is not with any refrigeration component or charge level. The problem is with the climate control.

Since I posted last night I remembered that I now have a service CD. I gave a quick glance at the CD and it appears that the problem may very well be a temp sensor. It looks like there will be some serious troubleshooting here.

Since the blower is running and air is coming out where it should, it appears that there is no flap or vac problem. It looks like a sensor or heater valve.

Now that the work week is starting I probably won't be able to do anything more until the weekend. I will keep you posted.

The CD has the proper resistance values for the temp sensor so you can double check it. The problem may also lie in the sampler blower (aspirator motor), but I do not know where that is hidden on your 124. On the 560 that was the final item needed to get the AC work correctly. In my case the blower was working but not efficiently, changing it cured the problem.

My problem was that the AC would blow on high, freezing you out, then when it adjusted speed, the interior would heat up until the blower kicked up speed. Basically the reaction was seriously delayed.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Hi Larry

You may want to double check the vacuum elements for potential leaks, easily accomplished at the switchover valve assembly behind the glove box. (<20 minutes) As you test the elements for leaks try not to exceed 3.5-4.0 inHg during the test.

One other thought, when the A/C system is turned off are you able to feel air passing through the ventilation system while driving down the road? If so you might have a Fresh Air/Recirc element that is contributing to the reduced efficiency at the vents.

Well, Mike may have been right with his first response. I read the "Checking Refrigerating Capacity" section and there is a chart that gives vent temp vs. Outside temp. The number I got yesterday matched ambient temp on the chart. It could be that the system is operating correctly.

What makes me suspicious is the fact that I have kept a dial thermometer in the vent for the last few years. In the past I remember the vent temp ALWAYS being right at 40F in any summer weather. Maybe my memory is wrong. I am entering my senior years after all.

I'm going to drive it at night with colder ambient and see if the vent temp tracks the chart.

Thanks for the replies. I have checked the sensor fan and it is working.

I will also try the system off/see if there is outside air check.

Have a great day,

I'm with you, Larry. I keep a thermometer in my vent and it is always at 42 degrees, except in stop-and-go traffic it will ease up to about 50 on a hot day.

__________________
2012 E350
2006 Callaway SC560

Maybe my memory is not going away after all. According to my reading, if the vent temp goes much below 40 or 41, then something is not working correctly. I'm sure this is to prevent evaporator freeze up.

Too bad, now I can't just believe the chart and leave it alone. I will have to continue my troubleshooting.

Thanks,

Larry -

It's probably worthwhile to pull the glovebox and test the vacuum actuators with a mityvac. It's an easy task and will determine whether you have any flap problems.

I'll place a bet that you've lost one or both portions of the fresh/recirc flap. The difference between cooling recirculated inside air and Texas outside air can easily add several degrees to the vent temp.

- JimY

jcyuhn,

Before reading the MB climate control information, my thought would have been that I never hit the recirc button, so this should have no effect. Since perusing some of this material, however, it seems that the climate control automatically sets it in recirc mode under super hot cabin conditions.

I will pull the glove box and test these units.

Thanks for the comments and experience sharing.

Have a great day,

jcyuhn,

Intuition is correct very often. In this case I hope you're dead wrong. Correct me if I'm wrong, but according to the book, the dash will have to come off to replace the recirc pod.

Have a great day,

Larry, you may indeed have a recirc pod problem.

However, I almost never put mine on recirculate and it blows about 42' anyway. I've never noticed recirc making a significant temperature difference on a 124. So your temp problem, I would guess, lies elsewhere.

__________________
2012 E350
2006 Callaway SC560

brewtoo,

Thanks for the response. In the past I have never pressed the Recirc button either. Yes, that was my thinking before perusing some of the MB service info. Somewhere in that reading I got the idea that the climate control unit will put the system in recirc mode if the cabin temp is high enough.

I hope my problem does NOT lie in the recirc pod. The thought of taking off the dash does not excite me. I should know tonight. I will pull the glovebox and check vacuum. If all vac is well, I am going to try to read the code pulses from the diag connector with an analog voltmeter. If that doesn't work, I'll rig up an LED.

Thanks again,

Larry -

Yes indeed, the dash does need to come off to replace the recirc pods - there are two of them. They are tucked on the far side of the heater box, hard against the firewall. You can just see the passenger side pod with the glovebox out. There's another situated likewise on the drivers' side.

The 124 actually runs the a/c in recirc mode most of the time. There are two recirculation levels available - 80% and 100%. Most of the time the car automatically selects the 80% mode. If it's hot enough out - Texas qualifies - it will choose 100%. About the only time the climate control will choose fresh air with air conditioning is in very mild weather - less than 75 degrees, perhaps.

Good luck, keep us informed.

- JimY