I'm trying to figure out how cold my AC should be and was wondering what other have for Evap temp values, or vent temp with a thermometer.

I was having trouble with the poor cooling and wildly fluctuating high side pressure. I replaced the TXV and drier, vacuumed the system and put in just under 36 ounces (I know a its a little overfilled) or fresh 134a.

The evap, and both heater core temps are all in the low to mid 50's F. The high side pressure is back down to 8 on the highway and up to 15 in traffic. No matter what I do I cannot get lower then 49F evap temp. The compressor is not shutting off and the low side pressure is 38-42psi, and nothing seems to effect it.

I just moved to DC for the summer and really want cold AC.

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1998 Mercedes E300TD

1983 Mercedes 240D Turbo, 131bar injectors, Cosworth intercooler and 63' Ford Falcon radiator, Ardic Parking heater, Headlight wipers, Best 38.6mpg.

1973 Saab 96 Rally Car, 1.8l V4 with all the race bits

The last thing you want to do with a 134 system is OVER charge it. If the performance is marginal, that may very well be your problem.

Find a Factory Service Manual for this specific car and it will have a table of vent temps vs. ambient temp. That will let you properly evaluate the system.

The best way to charge an evacuated system is by weight. Preferably a charging scale which will tell you exactly what weight you have removed from the container. Failing that, calculating the number of ounces and filling with that much from cans. Like say for 40 ounces, put in 3, 12 ounce cans a little of the last one. Since the system has no accumulator, it is best to err SLIGHTLY on the too little side, rather than too much.

Hope this helps.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Thanks Larry,

The system wants 2.2lbs or 35.2oz. I put in just shy of three cans, so at most 35.8oz.

I just found the factory specs for the w210 gassers. It looks like my low side pressure is about a bar to high and vent temp 10-15 degrees to high. Looks like I might need a new compressor, according to the MB sheet

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1998 Mercedes E300TD

1983 Mercedes 240D Turbo, 131bar injectors, Cosworth intercooler and 63' Ford Falcon radiator, Ardic Parking heater, Headlight wipers, Best 38.6mpg.

1973 Saab 96 Rally Car, 1.8l V4 with all the race bits

Probably not. Compressors don't fail that way. They don't lose performance by any significant amount.

Things that effect performance beyond incorrect charge amount are dirty condensor, dirty evaporator, too much oil in system, bad aux fan or controls, bad viscous clutch AND don't forget that the climate control controls the flow of coolant through the heater core to regulate temperature.

All that said, if you are taking these pressures and readings with the car sitting still, then they will vary. The key is enough air flow across the condensor. Driving down the road, this is no problem in most cases. In the shop with gauges and thermometers in place OTOH unless you have a high flow shop fan in front of the radiator and the idle set to about 1,500 RPM, it's difficult to check pressures and temps.

Good luck with it.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

I hope your right.

I've cleaned the condenser with soap and water, and fixed the aux fans so they run properly. The ccu does turn them on but only after the high side pressure is over ~15bar. I don't think they evap is very dirty since this system has filters on the air inlet. The viscous fan is working well and keeping the engine just below 80C most of the time. I have cleaned the duo-valve and the heater core temps are only 2 to 4 degrees higher then the evap temp, so I can assume little to no coolant is getting by the valve.


The low side pressure was taken with the car was stationary, but with varying rpm and cooling fan speeds. The evap temp and highside pressure were taken multiple times on a 8 hour drive. The outside temp varied from 68-85F with no change in evap temp and only minor increase in highside pressure from 7-9bar.

__________________
1998 Mercedes E300TD

1983 Mercedes 240D Turbo, 131bar injectors, Cosworth intercooler and 63' Ford Falcon radiator, Ardic Parking heater, Headlight wipers, Best 38.6mpg.

1973 Saab 96 Rally Car, 1.8l V4 with all the race bits

The Duovalve could be not shutting all the way off and some hot water is getting into the heater cores..

Yes, and there are many other maladies with the ACC that could be degrading performance.

It sounds like the OP has gone through the system reasonably thoroughly.

Sounds like the aux fans are working properly. Their main function is come on at excessive high side pressure in order to bring it down and that's what they're doing.

I think the system is coming up only marginally short of optimum performance.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution