AC not cold at idle

[85chedeng300D]

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?

[vstech]

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

[rick surgent]

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.

[85chedeng300D]

Originally Posted by rick surgent

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.

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)

[beerdavis]

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

[jbaj007]

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

[85chedeng300D]

Originally Posted by beerdavis

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

I'll try that!

[85chedeng300D]

Originally Posted by vstech

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

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.

[vstech]

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

[carnut]

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!

[85chedeng300D]

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.

[vstech]

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

[85chedeng300D]

Originally Posted by vstech

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

Excellent! That said, all I have to deal with is, find where the leak is and top off the system. I just hope that it doesn't leak in the internals of the compressor.

Is it possible that the refrigerant just disappears? Because I already visually inspected the entire system but did not see any visible and obvious signs of leaks. But I haven't used any UV light yet.

[jbaj007]

vstech is correct, and your gauge readings confirm it.

Unfortunately, the most common leak site is the shaft seal on the compressor. The R4's do that. Fairly easy to do (Autozone tool loan program), but requires recovering the refrigerant. Use the new double lip seal if it is the shaft seal.