AC problem 300 TD: not cool enough. - PeachParts Mercedes-Benz Forum

Richard Eldridge · #1 04-24-2007, 10:24 AM

I have been having a nasty time with the AC on my 300TD. When I bought it, it had a very slow leak, and was charged with R-12. I had a small tank of R-12 I found in a yard sale, and recharged it for several months, then I took it to a shop.

There I was told that the tube with the filler valve was the source of the leak and would have to be replaced: price of part: over $400. The system was checked for leaks and recharged with R-12. total cost about $1000. I got about three weeks of cool from that.

A year later, the same shop guy told me I should convert it over to R-134 and check it for leaks with dye. Trusting soul that I am, I did this. Leaks were found, the sight bottle was replaced, more expen$ive parts were found, and then I was told that the auxiliary fan stuck to the outside of the radiator wasn't working, and was assured that this was the ONLY remaining problem. Price of stupid fan: $400. I decided to buy the damn thing myself and install it. I found it finally on e-bay for about $75 delivered. It was made in Taiwan, but it fit fine, after I took the fan parts and mounted it in the old cage and stuck the old plastic shield on it. It was not hard to install, just two easy bolts to the braces in front of the radiator and a bracket and screw at the bottom. The electric cord plugged in easily.

The old fan groans and squeaks when turned by hand. My guess is that with new brushes and proper lube, it could be resurrected.

There was the wing of a deceased songbird behind the old fan and myriad insect wings and unidentifiable bug parts and bits of tiny gravel, all of which I carefully blasted out with a garden hose and pried loose with a plastic nail file.

The AC barely cools. There are no bubbles in the sight glass, and the auxiliary fan does not come on.

My thoughts are that the switch on the sight bottle (yes, I know they call it something else) is shot, and that is why the fan was so squeaky, because it had died of unuse. The shop guy told me that it was only the electric fan, but I tend to think that they really didn't check this out totally. I tend to think that there is an excessive tendency to throw expensive parts at any problem until it starts working.

Can the switch be changed without discharging the system? My guess is no.

What clever ploy can I use to check the new fan? I am pretty sure it is okay, but it might be defective.

Any thoughts will be greatly appreciated.

rrgrassi · #2 04-24-2007, 10:33 AM

You can check the fan by jumping it directly to the battery. On my 82, the fan is activated only by a heat activated switch on the dryer (what you are calling sight bottle).

You need to check the high and low side pressures with the system running and not running. It is possible that the freon leaked out again, or there may be a blockage either in the dryer or the expansion valve.

My car was converted to 134 before I bought it. It has the POS GM R-4 compressor on it. The front seal was leaking profusely.

JimmyL · #3 04-24-2007, 10:44 AM

Hey Richard,
Sorry to hear about your AC woes. Sounds like the folks you found are either dishonest, or just plain un-knowledgeable abut Benz's. Having said that, this is not a real complicated AC system, if you don't count the ACC unit.
The switch that operates your aux fan, as stated, is on the rec/dryer (sight glass thing), and does not penetrate the freon path. You can first try putting a 10amp fuse into the connectors that plug into the switch. Then just turn on the key and see if fan comes on. Or, try running 12vdc to the fan connectors. If fan comes on, your temp switch is most likely inop.
The aux fan will effect the final cooling of the AC, but it won't keep the air from blowing cool itself. My aux fan is not coming on in the Squash, but the vent temp still hits 41 degrees.
Report back and good luck