Well ive been reading alot about people rebuilding their entire A/C systems or just simply fixing theirs by recharging the freon. I have tried the freon, and no improvements. So I am pretty sure my system is broken somewhere. Can yo guys help me figure out how to trace the problem. I am not too excited about rebuilding it or swapping out every component. What are the different components in the AC system and how do I test each one to see if it is running like it should? It is summer now as you all obviously know... my AC blows air, when the engine is cool it will blow outside temp air.. but once the car is warmed up, nothing but hot air comes out of the vents. The previous owner converted to r134a he told me. I tried to fill it up, no luck. Still sweating in the 87 260e. If my air is blowing... what does that eliminate? What is working since its blowing? SInce my air is only blowing hot... what are the possible problems with the system?

ALso I think i overfilled the freon a little when recharging, is this bad?

So you mean hot air like when you have the heat turned up? If so you may have a faulty monovalve.

Does the A/C compressor actually engage when switched on? Feel the suction line with your hand - it is the thicker of the two lines going to the compressor and runs toward the brake booster on the driver's side of the car. It should be cool or cold, and sweating. If it's not, you have a refrigeration problem. If refrigeration doesn't seem to be an issue, clamp the lines going to the heater monovalve and see if the heat goes away. The monovalve may have failed.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

also check the fuse that powers the monovalve.... the valve may have not failed, the fuse could be blown.

i think the bottom line though....either the a/c compressor is turning or it's not. hopefully it's turning..

i have just gone through a compressor, drier, and expansion valve on my CE... lot's of work... did the PIA expansion valve...probbably didn't have to...

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


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If it is my compressor and I wanted to replace it. Does a 190e AC compressor fit? Are they the same part? I have a spare 190e compressor. If its the same part I could just replace mine and test.

I clamped the monovalve hose and still no cold air.. but it is not warm.. it is just room temperature air. I turned it off and turned on the AC and it doesnt blow air anymore. I remember that it does this... sometimes it works.. and sometimes it doesnt work. I checked the fuse and it is not blown. Any help here?

Also I touched my AC pipes coming from the drier and all the lines that is suppose to be supplying the freon are all hot.. and not cold like it should be. I tested my 85' 190e with working AC and the lines are all cold. What are the possible problems?

I checked the drier as well and it has more than enough r-134a. How come the pipes that are suppose to be cold.. are hot. I also listened to the compressor and it does jerk and spin when I turn on the A/C. ANY HELP WOULD BE APPRECIATED. thanks.. ive been burning up in this 105 F weather and i cannot stand this anymore

Also my aux fan infront of the condensers dont turn on.. wat could that mean?

The aux fan in front of the condensor turns on in response to two different circuits:

1. low-speed fan is tripped by the high-pressure switch on the receiver drier, in order to protect the A/C from excessive system pressures. This can be tested by jumpering the two wires coming from the red/green switch on the drier.

2. high-speed fan is tripped by a temperature sensor on the engine block, to protect the engine from overheat. This should trigger around 105 degrees, can be tested by jumpering the two-pole connector on the 3-pole switch on the top of the block.

If it never turns on, check both of these circuits.

Okay, how about my hot lines running out of the drier?I tested my other cars and they have cold lines, this car not only doesnt have cold lines.. it has HOT lines.