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#1
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A/C pressure switch
does anyone know if the pressure switch located on the receiver/drier is adjustable?
this is for a w123 240d I will be running a HC mix refrigerant that runs at lower pressures than r12. the cutout pressure on the switch is just a little too high for what I will need. I would like to find an adjustable pressure switch so I don't have to just jump it. The car currently has a universal receiver/drier with an aftermarket switch (stamped "made in Taiwan"). this switch has no adjustment screw. I will be replacing the receiver/drier with the correct parts. |
#2
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Changing the pressure of the cutout switch is going to accomplish nothing. It is NOT a cycling switch. It's in the high-side, so once the compressor first starts (IF it first starts), the pressure only goes up, so the low-pressure switch won't open unless you suddenly dump all of your refrigerant.
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#3
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what kind of freon are you using. It should still run the same pressures, just a different volume of fluid.
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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 |
#4
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Quote:
The OE switch closes as low as 10 psi. If you don't have that much static pressure in the system, there is no point in the compressor operating anyway. Last edited by tangofox007; 05-22-2009 at 11:57 AM. |
#5
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I agree..if you are having to jump that switch then something else is causing a problem...
... it will be over that minimum no matter what substance you use for refrigerant...
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
#6
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I think the stock low pressure switch is set higher than 10 PSI...based upon the one I just worked on it didn't close until the system exceeded 30 PSI. I guess if I were to be using a refrigerant which had a static pressure lower than that I'd just jumper the switch and not worry about it. If the A/C began to blow warm then simply avoid using it until you can recharge it or remove the jumper at that time.
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Marty D. 2013 C300 4Matic 1984 BMW 733i 2013 Lincoln MKz |
#7
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I checked the book for the W123 and the pressure varies substantially by model. Some W123 models are 10 psi, others show 29 psi.
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#8
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the switch for my car does close at 29psi. I am not using freon, I will be using a isobutane/propane mix (yes i know its flamable, yes i know the system was designed for r12, blah, blah, blah) For this mix to work properly I will be charging to ~20-25psi on the low side.
Is the switch on the high side? If it is I guess it wouldn't matter because I would be easily exceeding 29psi. Do you happen to know what w123 models have the 10psi switch? |
#9
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OK after looking at again I see that it is on the high pressure side. I should be able to use the stock switch with no problems.
thanks! |
#10
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Later 300D's with the R-4 compressor.
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#11
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The problem is when the system is at equilibrium both the high side and low side are the static pressure of the refrigerant. Depending on the temperature and the refrigerant used it might not be high enough to close the switch, though I would think static pressure of any refrigerant at temps warm enough to need A/C would be at least 30 PSI so the switch should be closed.
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Marty D. 2013 C300 4Matic 1984 BMW 733i 2013 Lincoln MKz |
#12
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Quote:
I cant seem to find a switch with anything lower than 29psi cutoff. I may have to just jump the thing. I'll just have to see what happens. thanks for your help |
#13
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It should be easy enough to come up with a pressure-temperature chart for your refrigerant. But what refrigerant only has a 30psi vapor pressure at any reasonable temperature? I don't think it would be a refrigerant that is worth using.
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#14
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The pressure switch is not adjustable. The spec of the switches are as follows. This is from the Official MBZ w126 manual. It should be similar for w123.
Low pressure - OFF at 2.0 bar, ON at 2.6 bar High side - OFF at 15.0 bar, ON at 20.0 bar. The manual uses BAR. You can do your conversion to psi, pascal. There are a lot of experts around here on AC.
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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed. W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html 1 X 2006 CDI 1 x 87 300SDL 1 x 87 300D 1 x 87 300TDT wagon 1 x 83 300D 1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry. |
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