The car is an '83 300CD.

AC is not cold when:
1) Ambient temp. above 80 deg. F and parked at idle.
2) Stuck in a bumper to bumper traffic.

But blows cold air when:
1) Ambient temp. around low and mid 70's, even when parked and idling or stuck in traffic.
2) Ambient temps. above 80 deg. F, as long as driving at speeds above 30 mph.
3) Whenever driving in the rain or at night.

AC system condition:
1) Compressor is cycling and functioning.
2) Compressor belt tension is OK.
3) Auxillary fan is cycling and functioning.
4) Assuming that it's still charged with R-12, because there are no signs of conversions, such as 134A retrofit stickers and fittings.

What could be wrong?
1) Low refrigerant charge?
2) Bad expansion valve?
3) Bad receiver dryer/filter?
4) Bad compressor?

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'85 300D Turbo - CA Version

well, you are going to have to get some numbers first. My guess is it's low, and the condenser is dirty. are you SURE the aux fan is running all the time? those symptoms really point to a bad or sporadic aux fan. remove the aux fan, get the condenser clean, remove the bugs and dirt/grass etc from it, and spray some degreaser on it and rinse it off well. test the temp sensor on the R/Drier clean the connections really well and put some di-electric grease on them. see if it helps. but most of all, get some guages and find out what the pressures are.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Had similiar problem in a 300sd. the climate control box was not shutting the recirc door in the system. So hot outside air was being allowed into the cooled air.

Based on your diagnosis, is it just the inadequate ram air flow across the condenser which is not making the AC cold at park and idle? I already power washed the radiator and condenser with the aux. fan out just yesterday because this was my first suspect. I even tried to install a larger diameter aux fan out of a W126 SD, everything was well until I shut the hood down and it hit the grille, so back to the stock smaller W123 aux. fan.

The aux fan only cycles on whenever the sensor is triggered by the high dryer temperature, that being said it's not ON all the time except when the condenser is hot.

I haven't checked the refrigerant pressures yet because I don't have the manifold pressure gauges in hand.

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'85 300D Turbo - CA Version

But the AC blows cold when running at highway speeds even if outside ambient temps is above 80 deg. The cold only disappears when the car is parked or lined up in a slow crawling traffic jam (about 5 to 10 ft per minute)

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'85 300D Turbo - CA Version

My 83 TD does the same thing when I am low on freon. I have a slow leak in one AC hoses. I top off with fresh freon in the spring and have cold AC for the summer. Check the freon pressure. Probably just low.
83 300TD
94 E320 wagon

Check the viscous fan clutch. Your symptoms match up well with a tired clutch. Engine operating temp OK at stop and go crawl?

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

I'll try that!

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'85 300D Turbo - CA Version

The engine belt driven fan seems to be pulling air when revved. But half-a$$ when at idle. Engine water temp stays constant at the dead middle of 80 and 100 line no matter what. It's just the AC acting up and not blowing cold when the car is not moving. But one thing I haven't tried yet is to see if it will get cold when engine is revved around 1500-2000 RPMs at park. I'll do it tomorrow and report back. It's kind of late now to rev the Diesel.

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'85 300D Turbo - CA Version

When you get the gauges on it at 1500 rpm for the pressure tests, do me a favor and heavily mist the condensor with water after you get all your readings. If the high side drops like a stone, consider the viscous clutch replacement/silicone oil refill.

http://acsource.net/acforum/viewforum.php?f=1

http://www.autoacforum.com/categories.cfm?catid=2

Use search on the above forums and you'll see what the MVAC pros think of old viscous clutches and high idle A/C temps.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

I tried to check the pressures earlier at work (I mean during the break), but I did it before I read your advise.

I just checked the pressures at idle, around 700-800 RPMs approx. and I didn't mist the condenser with water while checking.

Here are my numbers:
High side: 120 psi
Low side: 22 psi and drops to 18-20 psi whenever I slightly rev the engine.

What do you think?


Afterwards, I tried to mist/hose the condenser with water at idle and the AC gets cold but not as cold when the car is driving in the interstate or so.

I'll try the 1500 RPM pressure check tomorrow at work and see what I find out.

Thanks for all the infos jbaj007!

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'85 300D Turbo - CA Version

you are low on refrigerant.
get a can of 12 and adjust the charge to 32psi. look at the gauge, the little colored numbers correspond to boiling temp, you want the boiling temp to be above 32°F an easy way to test, is lay your hand on the cool suction line, when it flashes to the feel of a cold can of soda, you are pretty close to the correct charge. also, the sight glass on the receiver drier should flash clear of bubbles when you are full.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

You mentioned attempting to install the thicker fan assembly onto your 123. I did that on my 300CD and yes the grille rubs on the new fan! I loosened the hood hinge straps where they attach to the hood panel and pulled the hood forward away from the fan, the holes are already slotted. I also shimmed out the small rubber bumpers at the lower corners of the grille to keep the grille away from the fan while driving at higher speeds. I very carefully moved the hood latch on the radiator support forward ever so slightly so the hood release wasn't hard to pull to release the hood. Lubed the hood latch and hood hinges well and that was 4 years ago!

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Ambient temp: approx. 80 - 85 deg. F

Did the pressure test with the water hose misting the condenser at 1500 RPMs and here are the numbers:

High: 110-115 psi
Low: 15 - 20 psi

But I noticed that the AC blows cold in this procedure.
I haven't charged the system yet.

With this kind of difference between the High side and Low side pressures, theres no way that the compressor is shot right? But sometimes I wonder, because with the engine off, I can easily turn the compressor by hand.

__________________
'85 300D Turbo - CA Version

your compressor is working fine. you have not got enough Refrigerant in your system.
John

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!