A/C does not cool at idle

[jayhawk]

The a/c in my 89 300e does not cool when the outside temp is above 90 and it is at idle or stop and go traffic. Once the car gets on the highway for a stretch the air gets ice cold. I'm thinking that the V-fan clutch is bad, although, engine over heating does not seem to be a problem. At idle, I can stop the fan with my gloved hands. Can the fan clutch be removed without removing the radiator first? Is it repairable or does it need to be replaced? How can I test it? There does not seem to be much clearance between the raditor and the fan clutch especially when you factor in room for the wrench. Any thoughts?

[Mike Murrell]

Jayhawk:

If my memory serves me right, some MBs are designed to disallow compressor engagement when engine temps. are excessive.

Stopping a spinning fan blade by hand may not necessarily be an indication of a weak fan clutch, especially if the clutch is not engaged.

I would; however, disengage my hand from the fan blade area.

[SqueakyBrake]

Could be time for a freon charge. Check your sight glass, if it is foamy you need a charge.

Brother of The Benz, Jayhawk
To answer your questions lets go one at a time:
Not cooling at idle can result from
1. a low gas charge
2. low suction pressure resulting from a worn compressor or No. 1 or 3
3. slipping belt
Have your system checked by a technican if none of these are obvious.

Viscos fan clutch.
Most of these can be stopped as you have yours and still be able to perform satisfactorly.
To remove the fan clutch the radiator does NOT need to be removed. There are fan shroud retaining clips holding same to the radiator. By removing these in the up motion, the shroud is laid back over the distributor and the fan is exposed. You will need a special socket wrench and anti-rotating tool to remove the fan/clutch assembly. I'm not familiar with a test procedure for the thermostat in the fan/clutch and it is to be replaced. Fastlane has the tools and the fan/clutch.
Happy Trails Beep Beep from The Spiderman in Houston!!!

[Arthur Dalton]

The fan you want to be concerned with at high ambient temp is the aux. electric fan. That comes on by the high pressure switch at the reciever/drier. If you jump the two wires at the switch and the fan does not run, look into the fan circuit.
[ fuse, relay, etc]
If the fan circuit proves well [ when you jump the sw.], then you may be , as said, low on freon. [ not enough pressure to trip sw.]...or bad sw....

Improper air cooling of the condensor in any refrigeration system [ except water cooled] , will result in low perfomance. So will low refrigerant. Same problem, different diagnosis. Check both.

Brothers of The Benz, jayhawk,Arthur Dalton and blackmercedes
In correcting the inadequate cooling problem with all of your A/C units and discounting the parts that were replaced; the common denominator was FREON.
Jayhawk, get to that technican as suggested and have the system charged.
Happy Trails Beep Beep from The Spiderman in Houston!!!

[Arthur Dalton]

More than likely, low freon.
But the point is a bad condersor fan or dirty
condensor are often over-looked and diagnosed as low freon.
Same complaint, different fix.
So, for a DIYer , both sight glass and fan checks - condensor air flow, are where to look.

After that, go to a tech with gages.

[Mike Murrell]

Hook up the appropriate gauges before you drop any refrigerant in it.

If you are blowing "ice" cold air on the freeway, I'd wonder how it is you're doing this with an under-charged system?

[jeffsr]

These systems are famous for marginal performance at idle in hot weather, especially an '89 (which I have and get similar results). Even with the aux fan and clutched main fan, you are probably getting enough air flow to keep the engine temp within an acceptable range. If you raise the rpm's whilst at idle, you will notice a difference. Get yourself a small thermometer for AC work (AutoZone) and pop it into the center duct and check the temps at idle and at 2000 rpm. If your cooldown time is excessive, but it ultimately gets "cold", I'd be willing to bet you have lost some R-12 and will need a top up. Have it checked as advised, make sure fans are working and don't ever just sit in traffic.