summer is here and im using the a/c again, but theres a problem. its only cold when im accelerating. its been like this for a while so i dont think that its any measureable leak, but that it might just be low, at least thats what im hoping for. i replaced the evap coil about 2 years ago and it worked great last summer. im still on R12.

what could cause this? would a bad compressor do this or would it just not work at all?

thanks

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

how's the condition of the belt? could it be slipping? Also, how clean is the condensor?

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

It sounds like your " reserve capacity" is getting low.... a dozen things could be the cause...
I suggest that you clean and straighten the fins on your condensor and radiator...
This is something obvious which is different when going faster...
Also check out any aux fans you have...and and viscous clutches you may have... things like that could produce that symptom.....
Physics wise... the primary controlling factor on an AC system is ' air across the condensor' ....

Low charge = leaks.
Aux cooling fan not working.
Idle RPM to low.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

You may have a vacuum related problem that is doing something with the vac pods under the dash.

Good luck,

Learn to use the advanced search and FAQs. Use the names of the people who previously posted in this thread in your searches.

Learn the terms subcool, superheat, latent heat and sensible heat.

MB printed an HVAC manual for your car if you can find one. Don't be shy with your wallet or someone will beat you to the draw.

Read Lord of the Flies if you don't know the story and make the appropriate sacrifices to the appropriate idols.

having the same issue in my mom's '83 300 SD. will investigate over the weekend. if you find the problem, please post!

__________________
1985 300 D T - Rauchsilber (Smoke Sliver Metallic) with MB Tex Quartz 155 = Cream interior - 320K and counting!

1999 E300 TD - Silver - Just got her 3-13-15 !

the 2nd '83 300SD - Brown Metallic - traded away

1985 Limo Diesel aka "Stretchy" - Sliver - Blue Int - Sold but still in Athens

1983 300SD - Brown Metallic - Sold April 2008

1982 300 D T - Royal Blue with Tan interior - Sold

The clutch on the compressor can slip too.

this is true. Excessive gap is a frequent culprit, but there are other causes too. I once successfully diagnosed a slipping clutch by making chalk marks on both pulley and plate. Engage, rev it, and look at it with the strobe of a timing light. Of course, you'll need a gasser idling nearby.....hey, they got to be good for something, right?

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.