The AC of my 300SE (1989) is not working like is should.
Five years ago it was converted to R134 by an AC shop, they replaced the compressor, receiver/dryer, valves and hose.

Last year I replaced the condenser and it worked fine.
Now the temp fluctuates between 60 and 47.

Before I return to the AC shop for my yearly contribution (until now AC repairs cost me more than my DIY maintenance and repairs) I would like an (expert) guess of what could be wrong.

Rob

There's not enough info to even guess.

You need to hook up gauges and give us pressures to work with.

Good luck,

The fact that you have a lot of new parts is really of no diagnostic use.

Beyond that you haven't given much in the way of symptoms to go on. I am not sure of what you mean. Are you saying that the duct temp is going up and down that much as read by a thermometer stuck in the duct??

I believe your first step should be to identify the mechanism. The two immediate possibilities are: the compressor is cycling at too large a range (its off too much) or the mode door is working improperly. The mode or mixing door allows the choice of warm airconditioned settings for humidity control thus even though the compressor is on the temp can be anything. Is this the type of problem it is?

A poorly functioning refrigeration system can put out 47 on a cold day and 60 on a warm one... is that what we have?

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I mentioned the replaced parts only to show that the conversion has been done properly.

The temp fluctuates when measured with a thermometer struck in the duct. It takes about 1 minute to go down to 47 and then it goes up to 60 again, outside temperature is about 65. Last year it went easily down to 41 with high outside temperatures.

The compressor stays on. The small green lamp (arrow) in the switch sometimes goes out. If I look at the small window in the receiver/dryer I can see the fluid, no bubbles.

It was a pressure switch.
Now it goes down to 41 again.

According to my AC shop there should be a safety in the system. The pressure got high enough to kill the compressor.