I recently recharged my A/C system in my 94 e320 (r134a) because the system was low on refridgerant (but not empty). I did not vacuum the system and it was never opened to the atmosphere (no component replacements). Here is the trouble: the A/C system doesn't blow cold in the city, stop/go traffic, or even at 30-50 mph moving. The A/C works great on the highway (65+mph) it blows ice cold after about 5 or 10 minutes at that speed. Unfortunately I no longer have access to the set of R134 gauges that I used to do the recharge to double check the low/high side pressures. Any suggestions on troubleshooting before I purchase a set of gauges? I have heard a few things about the mono valve (or heater valve) but don't know how to test this part out or what the symptoms of a bad part are. Thanks!

Edit: My aux fans are working on both stages, I just replaced the fuse on the low speed relay and double checked their operation. It seems almost as if the condenser has slight blockage and only cools at high speed (when there is more than adequate airflow)??

Do a search on 124 a/c diagnostics or some such to find out how to use an LED to draw climate control trouble codes from the connector near the battery. If there is a bad sensor in the system, the trouble code will tell you which one.

Also, cut a 1cm square of paper and put it against the little grille near the rearview mirror. With the ignition key on the paper should be held against the grille. If not find and check the sample blower fan. On my car it is to the right of the glove box. It has been in several different locations throughout the 124 series.

Good luck,

I've tried to get the diagnostic codes out of that connector near the battery from pin 7 but every time I plug it in to test things out I blow fuse 7 (climate control). I've only tried it 2x both times with the ignition on and 1x with climate control off 1x with climate control on (A/C). Is this the right pin? I've used the LED diagnostic tool before on other pins so I know how to connect it and work it properly. Thanks!

Can anyone confirm/deny pin 7 as the correct pin on the on the 16 pin DTC box. Looking at ALLData its difficult to tell, it looks as if pin 7 and 10 are used for the climate control.



Thats the connector that I've got ^^

I'd like to help further, but my '88 has a different connector. If you had the service cd you could get this exact info.

Good luck,

hmm..well I'll try it again tonight. I'll also take a look at the heater valve, it can't hurt to just check it since it should only take a few minutes with a multimeter.

yo,
i just had the same exact problem, its the expansion valve. i replaced the compressor, which helped a little but the problem wasnt solved until i replaced the expansion valve. it regulates the pressure in the system. good luck

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

thanks for the tip...when you say you had the exact same problem you mean that it would cool sufficiently on the highway, at high speed, but not at low speed city driving...like me? Is there anyway to test the expansion valve?

Thanks for the heads up!!

How do you have the led tool hooked up?

+ to battery+
- to battery- (ground)
and the other plug to the pin on the 16 PIN DTC then I press the switch for 2-3 seconds and count the blinks. This setup has worked for pin 3, 8, and 14 but as I said, blew #7 fuse when plugged into PIN 7

Blk to pin 1
Red to pin 16
Odd to correct module pin

I'll give that a shot, thanks

OK..so as usual, the best advice is to start with gauges! My friend had a simple r134 recharge kit with a low side gauge. I plugged it in and at idle it was around 20psi (ambient temp 85-90F) I added some freon to bring the low side up to 35-40 psi and its cooling great. Obviously I have a leak in the system somewhere, once it blows hot again I'll add refidgerant with UV dye and check to see where the leak is. In the meantime I'll be praying to the evap. gods that it isn't the evaporator leaking!!!

Thanks for everyones help, I feel a bit bad because I should have known to check the pressures before asking for help, but thanks again!

Are the two aux fans working or else the compressor cut off except on highway the cooling will be sufficient.

the two aux fans are working great on both stages...as I said i recharged earlier this summer to ~40/285 psi (85F) and when i measured the low side yesterday it was around 20 psi (at 85+F) so that refidgerant must have gone somewhere...out i'm guessing