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What is the min temp the compressor will cut in ?

540itouring on Wed November 30, 2011 4:10 PM User is offline

Year: 1999
Make: Ford
Model: Ka
Engine Size: 1300
Refrigerant Type: R134a
Country of Origin: United Kingdom

Hi , i have a basic ford Ka of which i retro fitted a Aircon System from a second hand Ka and has worked perfect for 3 years apart from in cold weather . I use the car all year for work and use the AC all the time to demist the screens in colder weather and think the low pressure switch could be faulty as if the outside temp is 10 deg or less the compressor does not come on . The system has no leaks and a full charge and cools great in warm / hot days for a small car but not sure what the minimum temp required for the system to start up ? If i start the engine on a colder day the compressor does not come on until the engine warms the system and works perfect again. I saw when the plug was off the pressure switch it looks like it has a adjustment screw and wonder if a previous owner has tampered with it ?

I think i read in a manual of a older R12 car i had it would not function below 4 degs outside tem but with this basic R134a car no mention in the manual of the low temp in which it stops working . If you think to replace the switch i will do that as no problem as i am qualified and have all equipment but no one has confirmed the lowest temp at which the system should work . Thanks for all your help .

Karl Hofmann on Wed November 30, 2011 4:52 PM User is offlineView users profile

Generally speaking about 3-4 Centigrade is about right, 10c is a bit high.... pressure switches normally cut out at about 30c but there is a fair bit of tolerance plus or minus

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

540itouring on Wed November 30, 2011 5:33 PM User is offline

That would make sense of a temp of 3 to 4 deg . I was thinking it must be the LOW pressure switch that is causing the fault as the high works perfect in summer and the fault is only when weather below 10 deg and the static pressure (system off) will drop with temp ? what temp does the low pressure switch open ? about 50psi ? If that is the case i will check the switch with a meter on a colder day.

emileyair on Sat February 04, 2012 7:25 AM User is offlineView users profile

I guess 3 to 5 deg would be better

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NickD on Wed February 08, 2012 3:00 PM User is offline

With a typical CCOT system employing R-134a, requires at least 45 psi to close the cycling switch that occurs at 47*F.

For you British guys that kicked out your own English system of measurements and went to that crazy French system, 47*F is equivalent to 8.3*C or Celsius as you call it.

That's the temperature the AC system is exposed to, outside ambient temperature can be much lower due to engine heat under the bonnet.

I personally feel using that AC to defrost the windscreen is worthless, but then I am also not living on a tiny island in the middle of a huge ocean. With a CCOT system, compressor just cycles on and off like crazy wearing out the clutch and stressing the drive belt system. Hardly stays on long enough to remove what little moisture is in the air at those colder temperatures.

Oh, and 8.3*C temperatures in north Wisconsin is convertible top down weather. There, the windows never fog up.

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