1999 sl Ac issues aux fans dont run compressor wont engage

[Toomchisnvrenuf]

My 1999 sl500 I can't get the ac to blow cold. It appears to have refrigerant as the low side pressure line is cold. Front ac fans are not engaging and compressor clutch is not either. I have checked the 3 fuses listed on the card in the fuse box under the hood and they are ok. Could somebody point me in the right direction. I am hoping it is something simple like a pressure sensor/ temperature switch evap sw/ something like that. every thing in the cabin seems to be functioning properly.


Heres my Values:

01-74
02-76
03-89
05-96
06-163
07-5*6
08- 113
09-50*
10-135
20-00
21-00
22-00
23-00
2412.3
40-03
41-03
43-6-c
50-87*F
51-72*F
52-50*F
52-50*F
54-OFF
60- open
61-3.8
62-3.6
63-2.2
64-2.1
65-2.4
66-2.1

Anybody see anything that seems out of range?

Thanks mike

Thanks Mike

[slk230red]

Originally Posted by Toomchisnvrenuf

My 1999 sl500 I can't get the ac to blow cold. It appears to have refrigerant as the low side pressure line is cold. Front ac fans are not engaging and compressor clutch is not either. I have checked the 3 fuses listed on the card in the fuse box under the hood and they are ok. Could somebody point me in the right direction. I am hoping it is something simple like a pressure sensor/ temperature switch evap sw/ something like that. every thing in the cabin seems to be functioning properly.

If the compressor clutch doesn't engage, how did the low side pressure line get cold? Did you jumper the high side pressure switch at the receiver/drier?

[bobterry99]

Mike, what are your fault codes? The procedure is similar to the one you used to view the "actual values" and can be found in the manual dowloadable here: http://www.benzworld.org/forums/r129-sl-class/1266535-diagnostics-sl-pre-94-a.html?.#post2342164.

[Matt L]

Originally Posted by slk230red

Did you jumper the high side pressure switch at the receiver/drier?

It is not a switch, it is a transducer. Jumpering any of the contacts could cause severe damage. Don't ever attempt it on these cars (or any other with a three-wire "switch").

[slk230red]

Originally Posted by Matt L

It is not a switch, it is a transducer. Jumpering any of the contacts could cause severe damage. Don't ever attempt it on these cars (or any other with a three-wire "switch").

Yes you are right.
Mine is a 2 wire...low on freon and the compressor clutch will not engage. I jumper it to add freon after evacuating the system. No problems.

But his compressor clutch will not engage and his low pressure line is cold. Yeah, that makes sense. So I guess if his freon level is ok and his clutch doesn't engage, and his low pressure line is cold, then he is getting A/C without using the compressor.
Got it!

[Matt L]

Originally Posted by slk230red

Mine is a 2 wire...low on freon and the compressor clutch will not engage. I jumper it to add freon after evacuating the system. No problems.

But his compressor clutch will not engage and his low pressure line is cold. Yeah, that makes sense. So I guess if his freon level is ok and his clutch doesn't engage, and his low pressure line is cold, then he is getting A/C without using the compressor.
Got it!

His description leaves something to be desired. But nonetheless, his car is different from yours, and it is not possible to jumper the pressure sensor. Attempting to do so may destroy the rather expensive climate-control pushbutton unit.

To charge these, you must put enough in as a liquid to trip the switch before you can charge as a vapor (unless you introduce a complete charge as a liquid instead).

[slk230red]

Originally Posted by Matt L

His description leaves something to be desired. But nonetheless, his car is different from yours, and it is not possible to jumper the pressure sensor. Attempting to do so may destroy the rather expensive climate-control pushbutton unit.

To charge these, you must put enough in as a liquid to trip the switch before you can charge as a vapor (unless you introduce a complete charge as a liquid instead).

Again, you are right. I was thinking of the 2 wire on my W201. I couldn't figure out how he knew his freon level was ok and his low pressure line was cold if his compressor clutch was not engaging.

[Matt L]

Originally Posted by slk230red

Again, you are right. I was thinking of the 2 wire on my W201. I couldn't figure out how he knew his freon level was ok and his low pressure line was cold if his compressor clutch was not engaging.

I'm wondering about that one also.

There is only one way to be sure that the refrigerant level is right, and that is to evacuate and recharge. Of course, if you have a system that puts out cold air and has the proper pressures, you can pretty much assume that the level is good.

If the compressor is not running, there is absolutely no way to know that there is enough refrigerant in the system without reclaiming.

[Toomchisnvrenuf]

I hooked up a set of gages and the system read high on pressure. We let out some of the pressure and then added freon to the point were the gage read full. Felt the line and it was cold as was the dryer. The compressor nor the aux fans engaged. I did unplug the pressure switch and the fans ran, plugged it in and the fans stopped. no cold air is coming out of the vents. I have purchased new pressure switch, dryer, temp switch and evap switch. and o-rings.

Thanks Sorry for the vague description but I moved this post from Benzworld, and it lost some meat in the transfer.