The temperature is well below freezing because you can start to see frost shooting out of the vents after a while. This car only has 2 pressure switches on the high side of the circuit. One that prevents the clutch from triggering if the system doesn't have a minimum amount of refrigerant pressure before switching ON, and another to turn off the compressor when the pressure in the system reaches a maximum pressure threshold. In this case the second switch is never triggered. I have to switch it off manually after about 1 minute because it gets too cold. 12oz of duracool does the job of 2lb of R134.

Apparently you are not aware how Mercedes climate systems operate. They do not use a pressure switch for clutch cycling. The pressure switch on the dryer is strictly a safety cutout for overpressure/underpressure. Clutch cycling is controlled by an evaporator temperature sensor - basically a thermistor mounted in the airflow immediately after the evap. I forget the setpoint to trigger compressor cutout, but it is well above freezing.

Mercedes does not cycle the compressor to regulate cabin temperature. If the cabin becomes overcooled the climate system begins pulsing the monovalve to admit hot water to the heater core. Air passing through the HVAC box first goes through the evaporator to be cooled & dehydrated. Then it passes through the heater core, where it is (if necessary) warmed enough to keep the cabin at the set temperature. Cycling the compressor to control cabin temperature isn't used because it would not be as comfortable - the air would not be dehumidified - and it wouldn't be safe because the windows would fog under specific temperature/humidity conditions.

On a clutch cyling orifice tube system (as used on most cars from U.S. manufacturers, but not Mercedes) the cycling switch measures the low side pressure, not the high side pressure. The compressor is switched off when the low side pressure (and hence the evaporator temperature) drops below the setpoint. If you check the vapor pressure curve for propane (R-290) you will find it is much, much higher pressure at any given temperature than is R-12 (or R-134a, for that matter). So yeah, the compressor isn't going to cycle because the low side is never going to drop low enough to trigger the clutch cycling switch. Of course, the high side runs much higher too, so you're at risk of triggering the blowoff valve if your car has one, or just breaking the compressor or blowing out the condensor.

If ice isn't forming on the evap, then it isn't below 32F/0C. I'm guessing your thermometer is significantly innacurate.

Apparently you weren't reading.
I was talking about my Volvo R134 system that has been converted to duracool which runs at 25f. My W201 also using duracool stays between 40-50f no matter what I do. The nice part about the W201 is that it will maintain this temperature no matter what the outside temp or speed. I spent 30 minutes in stop and go traffic yesterday at 100f outside temp with the vents blowing a cool 45f. Can't go wrong with that.

what pressures are you running with the duracool?

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Do you know the critical temperature(s) for Duracool?

That evaporator would soon be a solid block of ice.

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2012 E350
2006 Callaway SC560

You're right. This thread started out using grill gas to goose an a/c system.

I plan to continue not reading in the future as well.

Unless the ambient dew point is below 25°F, which is nearly impossible on a hot day. So yes, the evaporator would quickly be a block of ice. The thermometer needs to be calibrated. Use a glass of water filled with ice cubes to calibrate it at 32°F.

Must have been about 38F outside to get vent temps like that.

If that is legit, congrats, but I've dealt with MANY A/C systems and temps like that are simply impossible w/o the evap freezing up.

Looks like critical temp for isobutane is 134C and for propane it is 96C. For R-12 it is 112C and R134a is 100C. I'm thinking critical temp would not be a problem when using DC in an R134a system, but I'd be concerned that it might be reached in an R-12 system.

I can take a similar picture, and make my thermometer read colder than yours.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Hi just to add to this thread I have been running R12a in my 300E for the past year with no problems .R12a is a mix of butane and propane ,down here in Puerto Rico its legal and cheap.
My system was converted to R134 but was never very cool the change to R12a dropped the temp at the vents by 20 degrees!!
Anyone interested should do a search on the web for info on R12a.
I plan changing the gas in my 420sel when the AC needs work . Steve.

The piece of body separating the engine from the interior which would what normally be called "fire wall" is not called firewall anymore. Most manufacture call it the "bulk head" True story: A woman was driving her vehicle & a fire stated in her engine bay. Well she pulled over & stayed in her car, supposedly called for help but stayed in her car with the mentality of the "fire wall" being fire proof. Well She died, the family sued the car company. The family won & now most manufacture call it a "bulk head"

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6

How did they know she had the mentality and presence of mind to stay in the car because it was called a "firewall"? Dead people cannot testify and argue their case.

If she called for help, didn't anybody tell her to "GET OUT OF THE CAR - NOW!!"

There's a lot missing to this story.

I read about using hardware store propane as a refrigerant some time ago and have been wanting try it; however, I've seen information that says propane can be a problem. Some because it won't carry the oil through the system, and others that say it will freeze up.

It seems the commercial HC refrigerants, Duracool - Enviro-Safe, are a blend of propane and isobutane, but whether the addition of the isobutane is to carry the oil or prevent freeze-up isn't clear.

I'm just curious to know if you've experience any problem with your all propane setup.

I've used both Duracool & Enviro-safe and they worked great! The only problem is that having them shipped now incures a "hazmat charge", making it pretty expensive. The idea of using cheap, locally available propane is very appealing!

I love to know how your setup is working out. Thanks!

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire