refrigerant leak
 

my E240 2004 leaks a small amount of refrigerant every 3-4 days (i know it by reduced cooling) and I am keep charging.

One technician in the workshop said there is no leak anywhere but expansion valve and dryer are choked and causes the gas to discharge from an automatic safety valve on the comressor....does it make sense??

If those were faulty, the system should not cool perfectly when i top up refrigerant. what say???

I have the dual zone a/c without the LCD and can't diagnose like the E320 :(

By using refrigerant with dye & then a black light...you should be able to find a leak.

If your compressor is venting refrigerant, there should be oil all over it.

The dye and blacklight is nice, but it won't show anything if your leak is not in the engine compartment.

Use a sniffer, if you have it. The way to check the evap (the way I use anyway) is to turn the A/C off, and the fan to full for about 10 minutes; this could clear out any moisture that can cause a false reading. After that, turn everything off, close/tape off your vents and wait for about 5 minutes then "sniff" the condensate drain tube. You've got a decent sized leak, so it should be pretty apparent if it's inside.

If you don't have a sniffer, evac the system and charge it with nitrogen. Tell everyone to quit making noise, shut the shop doors and listen for the leak. I probably find 9/10 leaks using nitro. Now, don't laugh, but if the air is relatively still, you can locate the source of the sound (in the engine compartment) by using a stick of incense - just watch the smoke; it'll pick up even the slightest airflow. If it's inside, you should be able to hear it easily with all the doors shut (and the vents unsealed). Again, you have a decent sized leak, so you should be able to hear it.

A bottle of Super Blu is a good thing to keep around for leaks as well. It stays in liquid form from -30degF to 200degF. Spray it on fittings, hoses, etc... It will bubble up (and stay bubbled) on even the smallest of leaks.

Just don't put any refrigerant with that stop-leak crap in there. You will regret it.

+1 This is excellent advice.