W126 560SEC Air conditioning issue cooling on AUTO and HIGH - PeachParts Mercedes-Benz Forum

PV560SEC · #1 07-03-2021, 08:36 PM

Hi, I just picked up a 1991 560 SEC. When the AC is on, at low speed it cools while driving. When stopped for more than a minute or so, it seems to stop cooling. When using the AUTO button it blows a lot of air, but not cold air. Same when using AUTO and setting the temp dial to the lowest setting. Any help would be appreciated.

The AC system was last recharged in mid 2019.

Thanks for your help

Usaguy · #2 07-03-2021, 08:52 PM

hook up gauges to the high and the low side and see what the readings are.

Also is your aux fan working and what is the engine temp in traffic?

nulu · #3 07-03-2021, 10:14 PM

Sounds like youve got a leak, evacuate recharge

PV560SEC · #4 07-04-2021, 12:23 AM

I will have my tech hook up the gauges.

Aux fan does not come on when i switch on the AC. Is it supposed to come on right away, or once the car reaches operating temperature? Checked Fuse 1 and reseated it as it did look a bit off in the holder. Curious, about the fan operation and when it comes on.

Driving home yesterday, the temp was right at 80 and outside temps were between 90 and 93, freeway driving. Freeway stopped to dead stop, and car idled for about 10-12 minutes with AC on, and temp went between 80 and 100, around 90.

Thank you

PV560SEC · #5 07-04-2021, 12:25 AM

Quote:

Originally Posted by nulu

Sounds like youve got a leak, evacuate recharge

Car is going in next week for an oil pan leak, so will have my tech check this out. See my reply to Christuna - is the AC fan supposed tp come on as soon as the AC is turned on, or does the car have to heat up first?

Thank you

Usaguy · #6 07-04-2021, 07:12 AM

Your engine temps look alright and the aux fan doesn't come on right away. It has either a pressure or a temperature switch sensor located on the high side of the system

PV560SEC · #7 07-04-2021, 05:19 PM

@christuna so drove her today. AC definitely works slightly better on low fan. Climbed for about 1.5 miles, temp rose as shown in the pic. Normal temp also shown. AC on the whole time. I got home after a 8 mile drive, and the aux fan was not on. I think the first step is a evacuate and recharge and see if that helps with the pressure etc. Any thoughts? Thank you

Usaguy · #8 07-04-2021, 06:13 PM

Quote:

Originally Posted by PV560SEC

@christuna so drove her today. AC definitely works slightly better on low fan. Climbed for about 1.5 miles, temp rose as shown in the pic. Normal temp also shown. AC on the whole time. I got home after a 8 mile drive, and the aux fan was not on. I think the first step is a evacuate and recharge and see if that helps with the pressure etc. Any thoughts? Thank you

Your engine temp looks perfect.

Why evacuate? Checking the high and low a/c pressures can tell you a lot about the condition of the compressor and the expansion valve.

They rent ac gauges for free at autozone

Second thing that I would do is probe the a/c compressor clutch and install a light on the dash when the clutch is activated so that you can check if maybe you have an electrical problem sometimes and that the climate system doesn't activate the clutch.

PV560SEC · #9 07-07-2021, 11:03 PM

So it seems its still R12…..its going to. R134.

PV560SEC · #10 07-09-2021, 08:07 PM

The tech confirmed we will have to switch to R 134. Seems a pretty simple procedure.

PV560SEC · #11 07-13-2021, 10:16 AM

So the AC system was recharged yesterday - all is well, cools beautifully and the aux fan operates as intended. There was almost no Freon in the system, that was recharged 4 years ago, so leak detection dye has been put in, and we will check this in a couple of weeks. Seems these cars keep a Freon charge better if the AC is used regularly, and so that is my intention. Thanks for the help.