94 w124 Air Conditioning problem

[skiier3_9]

On my 94 e320 my AC works moderately well if the car has been in the shade or other cool area but doesn't seem to be able to "catch up" with the heat and cool sufficiently if the car has been sitting in the sun. At low fan speed i can feel that the air coming out is cool but when the fan is on high (or auto) the air isn't cool at all. After about 30 or 40 minutes of driving around like the A/C is finally caught up and the car is cool. I would expect that it should only take about 5 or 10 minutes for the AC to feel cool on your face etc so i suspect that something isn't working properly. Where in the engine bay can I check the refrigerant level (where is the compressor?) Or is this likely a different issue.

http://image.inkfrog.com/pix/houstoninc/DSC04589.JPG

BTW: I read in a different post that all 94 cars had R134a - can anyone confirm this? If so, I should be able to recharge the system myself (if it is low that is).

[engatwork]

You need a/c in Minn?

You may just be alittle low on r134 (yes it uses 134). I would insure that the electric fan in front of the condenser is coming on when it is supposed to too. Get some gauges on it and come back with the pressure readings/ambient temperature.

[schumi]

there is a sight glass behind the driver side headlight. look for bubbles.

[Mike Murrell]

If the system is 134, the sight glass can be very misleading. You need gauges to check 134 pressure.

[skiier3_9]

hmm...so am i better off taking this to an A/C specialist or can i work on this system myself? I do virtually every other repair necessary on this car and our 190e so I'm fairly competent with a wrench. If I go to an auto parts store can I find the equipment to test my system pressure? I'll run the car with the AC on and check to make sure that the fans are engaging and the compressor is running. If i set the temp wheel at 65 and the fan on hi the compressor should run enough to kick the aux. fans in right? That should/would also tell me if the system was low on 134 (ie if the fans did not come on)

[Arthur Dalton]

I was going to mention that if you had no gages..
usually, the aux fan should come on at ambient 75F at idle if there is enough refrigerant to trip the high side pressure sw... if not , try a little bit of rpms..
It is a good idea to jumper the fan high pressure sw first to be assured of the circuits integrity.. than you know it is pressure related [ vs electrical fan circuit] if it does not come on....
..just remember, the aux fandoes not always come on with a/c compressor on that model... it only comes on when there is a high heat load, and that takes at least 75F ambient to get accomplished..

[skiier3_9]

wheres the high pressure sw to jumper to test out the aux fans. I suppose I can idle the car out in the heat (its been like 80 something here) with the AC on to see if the fans kick in. Do the aux fans have a temp threshold to come on as well? The 190e 2.3 had an engine block temp sensor for the aux fan that would trip the fan at like 87 or 90 degree C. Anything similar to that on the m104?

Thanks for the help!!

[Arthur Dalton]

The aux fan does have a coolant temp sensor for high speed when coolant gets to 105C, BUT , that has NOTHING to do with the low fan curcuit, which is refrigerant a/c pressure activated. This sw is on the drier/reciever near the driver headlamp. It has a pigtail on it and you can jumper the feed wires ..that will [should] activate the LOW speed aux fan...which is what should happen under thermal heat load when there is enough freon/pressure on the systems high side [ condenser].. all the fan does is helps keep the high pressure in check at high load to aid in cooling and not let the pressure get so high that it kicks out the compressor...that is why it does not run all the time [ as in low thermal load conditions]

The confusion comes from many cars being wired to have fan on whenever a/c system is on .. not on this chassis..it is an AUXILLARY fan...meaning just that.

[kggkgg]

Is it that the air flow is powerful but just not cold enough or could it be the air flow is not strong enough.

a wild card idea but I had the latter problem which turned out that some previous owner/tech had fitted the blower backwards which surprisingly gave reasonable air when stationary but very little on the move (as it was fighting the natural air flow). Turned the fan around and now I have lovely cold air

just an idea

Keith

What you describe could very well be a vacuum pod on the fresh air door not operating correctly. I would check the refrigerant level with manifold guages and a thermometer. If it appears to be somewhere near properly charged, your problem is then almost definitely a problem with the fresh air door. In really hot weather it should not be allowing fresh air until the cabin is cooled down really well.

Good luck,

[gpracer]

According to my gauges, the low speed fans come on at about 250 psi on the highside, and turn off around 180-190 psi. NOTE: I have R-12 . If the ac worked before and now it cant "hold a thermal load" or in other words cant keep up, its probably just low on freon.

[y2kimmel]

Don't forget to check if the low-speed aux fan resistor is working as well. Mine was shot, with crappy A/C as a symptom. On the E420 it took a while to replace - hard to get to, but the 300E should have a bit more space for working on it. i think the part was $40. Mine was corroded and obviously burnt.

troy
1995 E420 95k

Whether the aux fan works or not will have little to do with ac performance and capacity. That is NOT to say you should not worry about the aux fan working properly. It's purpose is to bring down dangerous high side pressure for system protection, thus it is very important.

Have a great day,

[skiier3_9]

thanks for all the suggestions, i'll have to check out the aux fans and find some tools to check the pressure of the system. I know that the blower is installed correctly as there is plenty of air flow its just not cool enough. About the vacuum pod on the fresh air door, when i start the car i hear this vent somewhere under the dash move (i can't tell if its open or close) is this normal? I suspect that this fresh air door could be the culprit, but who knows.

[skiier3_9]

ok, so what sort of pressure gauges do i need to check the pressure in the system and where could i buy these gauges?

Also, once I get the gauges where do i check the pressure? Thanks!!!

I'll attempt to measure the temperature of the air at some point and post the readings.