W124 AC works at speed, but not at lower rpms - PeachParts Mercedes-Benz Forum

arcteryx · #1 07-03-2009, 12:57 AM

hi. I have a 92 300d 2.5. The air conditioning blows nice and cold when on the highway. However, once in stop n' go traffic, the air is not very cold. The RPMs obviously fluctuate around town. Any ideas how to make it cold on low RPMs? TIA.

Matt L · #2 07-03-2009, 01:05 AM

It's as likely a problem with low speed as low RPM. Try cleaning the airway through the condenser and radiator. After seventeen years, it probably needs it.

compress ignite · #3 07-03-2009, 01:12 AM

At stationary rests (Stoplights) and idling around town without the added airflow
of the Auxiliary Fans (They come on Low Speed at high pressure of A/C system)
Red pigtailed (Two Wire) sensor screwed into the receiver/dryer senses and
turns on Low Speed Fans.
'Pull back the insulation at the connectors and "Jumper" the two wires with the ignition key ON,you should get Low Fans.

arcteryx · #4 07-03-2009, 09:51 AM

Well, I am glad to hear this is not normal and can be corrected.

Matt- where is the airway located? Are you referring to the vents near the wiper/cowl area?

Matt L · #5 07-03-2009, 10:28 AM

I'm referring to the spaces between the fins on the radiator and condenser. That's where the air flows.

Ken300D · #6 07-04-2009, 06:52 AM

Has your AC system been converted from the original R-12 to R-134a?

And does your auxiliary fan come on in stopped traffic?

Ken300D

04 Diesel · #7 07-04-2009, 10:29 AM

Check you auxiliary fan fuse, mine did the same thing. Pull the fuse and look at it, my fuse looked fine until I took it out and it broke in half. Put a new one in and ac works good now.

arcteryx · #8 07-05-2009, 02:14 AM

Yes its converted to 134a. Looking at the fans, the PS fan spins. the DS one doesnt. Should they come on at the same time? I'll check the fuse too.

EDIT- Did some research- its a dual stage, so they wont come on at the same time at idle. The fuse is fine. Still perplexed....

i-osprey · #9 07-06-2009, 06:45 AM

I have a similar problem and I can't track it down either.

I'm also running about 100C now on the highway and I worry that it could be that my aux fans aren't working properly.

Occasionally, I have noticed that the passenger side fan won't be on or will come on intermittently.

I replaced the fuse after it stopped cooling all together one day and that seemed to help but it still underperforms in city driving.

amg280 · #10 07-06-2009, 10:24 AM

Mine also underperforms in city driving. I have a brand new evap with expansion valve and new reciever/drier. Ice cold on the highway, but in hot stop and go traffic, it leaves something to be desired. Could be a week compressor I suppose, barring all the cooling fans, etc. work.

I find this to be very common on older benzes.

TimFreeh · #11 07-06-2009, 11:19 AM

Quote:

Originally Posted by amg280

I find this to be very common on older benzes.

I've found it to be common on W124's that were converted to R134a - systems that have a correct charge of R12, a clean condenser and working Aux fans will produce nice cold air in stop-and-go traffic even at ambient temps in the mid 90's.

amg280 · #12 07-06-2009, 11:23 AM

All of my W124's were factory filled with R134a. Unfortunetely I have never experienced one with an R12 charge. Perhaps theres a refrigerant other than R134a that will yield better results. I heard of some, freeze cool, duracool, etc.

arcteryx · #13 07-06-2009, 11:23 AM

I know there are some newer products in lieu of r12/r134a- does anyone have experience with these? AC is mandatory for the 100+ degree weather in Texas.

i-osprey · #14 07-09-2009, 11:37 PM

Well, today was our hottest day(107F) so far and my car almost got into the red on the gauge.

The A/C was cooling ok on the highway but was doing nothing in stop and go.

I popped the hood to check the fans and lo and behold neither aux fan was turning.

I even had to turn on the heater full blast on hilly sections with the wind behind me.

I am going to check the fuse again but I don't understand why I would keep blowing fuses if both fans spin freely(they do).

This is a major pain now that it's so hot.

How do you "jumper" the red plug on the evaporator mentioned above and have it turn on the fans?

Do you run a wire from the battery?

How else would it get power?

E150GT · #15 07-10-2009, 01:13 AM

heres my take on this. I don't think even in R12 trim these cars can really cool you in stop and go traffic like we"d like. This is for Texas at least, the Northern peeps might beg to differ. As for the aux fans, I think they do help a lot, but it seems people think they are the end all in stop and go traffic cooling. I think its the condensor. I think that a parallel flow condenser coupled with dual working aux fans is the key to succes, as that is what is in my ex- girlfriends ML320, and that car can make you numb in texas stop and go traffic as can my dads F150 (1995). The thing is is that the f150 has no aux fans and the temperature only creeps minimally in traffic, and the system is still sealed since the day it left the factory. It relies soley on the fan clutch to draw air across the condensor. Someday I might prove this theory of mine by upgrading my conndensor and maybe putting dual fans up front.