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38F at the vent

Matt L on Sun June 15, 2008 12:54 PM User is offline

Year: 1996
Make: Mercedes-Benz
Model: E300D
Engine Size: 3.0
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 26
Pressure High: 170
Country of Origin: United States

I just got my system back together. I disassembled everything, but I had to flush the evaporator and its lines while they were in the car. The evaporator is like any of them and extremely hard to remove, and its lines are hard enough to get out.

I used the HECAT pulsating flush gun and HECAT fluid for the flush for everything but the compressor, condenser and dryer. I flushed the compressor with 64oz of DEC PAG-46 oil and it was still discharging a slight green from the dye that was in the system. I replaced the condenser, dryer and TXV.

I'm guessing that the compressor was still holding about 2oz of oil even after draining, so I put an additional 5.5oz of oil into it and the new dryer. I installed the old dryer first to ensure that the rest of the system would hold a vacuum, and it seemed to hold just fine overnight. I'm going by the gauge on my set rather than a real micron gauge, but the needle didn't budge at all. I then installed the new dryer with its oil and vacuumed the system again for an hour, shut off the pump for an hour to check for leaks and moisture. I saw no movement of the gauge over an hour without the pump so I turned the vacuum on for an additional two hours before charging with refrigerant.

I charged it as a liquid, mostly into the high-side line but a few ounces into the low side as well. Then I turned the compressor shaft by hand. Lots of times.

The pressures above are from running in the garage, so the car was not only in the shade but it was in an air-conditioned space until I opened the vehicle door to run the engine. I was seeing 44F on the left-side center vent and 42F on the right. On this car, a slightly low charge causes the left-side center vent to become very warm compared to the right-side center vent.

Driving the car showed similar readings. I was seeing 9 bar high-side pressure while driving 55 MPH, and still getting 44F out of the left-side vent. When I came to a stop, the high-side reading slowly climbed to 14 bar causing the auxiliary fan to come on at low speed. The high-side reading remained at 14 bar but the vent reading dropped to 38F. This is all with the fan on medium, temperature controls set to LO and recirculate turned off.

Special thanks go to AMA, HECAT and this forum.

TRB on Sun June 15, 2008 1:47 PM User is offlineView users profile

Seems to be working pretty well. On top of that it's a MB conversion which I personally have not had a lot of success with. Good job!


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Matt L on Sun June 15, 2008 1:54 PM User is offline

It's not a conversion; it was 134a from the factory.

It came apart due to extremely poor performance. The high-side pressure was spiking to 350psi with only 15oz of refrigerant in the system (told to me by the shop that reclaimed my existing charge), and there was essentially no cool air from the left-side center vent. The full charge is 1kg (2.2 lbs).

The problem was a plugged dryer. The line from the dryer to the TXV was quite cold to the touch with the compressor running. In addition, the high-side pressure and temperature sending units are on the outlet of the dryer, so the system didn't even see the high pressures that were being generated.

TRB on Sun June 15, 2008 3:08 PM User is offlineView users profile

Need a nap I thought it said 1986!


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