240 1989 240 Air Con pump stays engaged (rotary style switch)

morch_66479morch_66479 @morch_66479 Melbourne, VIC
edited June 21 in Troubleshooting


I've had my air con re gassed and all was working fine up to last when I noticed that the compressor doesn't engage & disengage once i turn the knob past the 3 clock position.

What's people's views on this? I heard the knob works better in hotter climates and prevents the condenser from freezing up.




  • carnut222Greg S @carnut222 Daylesford VIC

    Can you please provide a bit more info? Does the A/C compressor come on and the A/C gets cold?

    Sounds like you're saying it works OK as long as you don't turn the knob past the 3 o'clock position. If you turn it to 4 o'clock or farther around, the A/C compressor stays on? Then what happens, does it still blow cold air? If that's the case, you may have it gassed up with HyChill (or hydrocarbon equivalent) which seems to get colder...so just turn the knob to 2 o'clock and live with it if it cycles fine there. Otherwise we need to know more. It could be over or under charged.

  • Sounds like the A/C is inopereable after the thermostat switch is turned past 3 o'clock. that points to the thermostat switch (in the dash) as the likely fault.

    As Greg says, if you can live with it don't turn it past 3.

    Also test turning it all the way around to about 9 o'clock - as far as it will turn. What happens then?

    Greg probably has a couple of spare thermostat switches.

    As it is 10 degrees here in Melbourne at the moment, maybe it is just working normally as it is already cold enough :-) Try running the heater to heat up the cabin proper hot then see if the thermostat switch works.

  • I'll give the above options a try today and let you know what the results are,

    The A/C compressor itself works fine and creates cold air in the cabin but it just didn't click in and out like it used to when i turn it past the 3 clock position. The pumps stays running all the time which isn't good for the system i hear.

    The gas used is R134a and the compressor kicked in and out before with no issues.

    How can i check if it's under charged? Need a specialist to look at it i guess?

  • carnut222Greg S @carnut222 Daylesford VIC

    What year is it? I'm assuming pre-1990 since you have the rotary dial. It may have a sight glass on the receiver/dryer bottle that should be mounted on the side of the radiator support behind the RH (driver's side) headlight. If it has a sight glass, turn on the A/C (with the car running obviously) and see if you can see bubbles in the sight glass. That can mean its under-charged. The only way to know for sure is to take it to an A/C place or mechanic who has the A/C gauges and they can test the pressures.

  • Mine is a 1989 model, i took a video of the sight glass - https://www.youtube.com/watch?v=UJJ__RDHsBk

    So i ran the the A/C with full heat and full cold whilst set at the 6 clock position but the pump just stays constantly engaged. A/C is working but just don't like the idea of having the pump engaged at all times.

    Greg, have you some spare thermostat switches for me to try out?

    Otherwise i'll be taking it to an A/C specialist.

    Thanks for your help guys :)

  • carnut222Greg S @carnut222 Daylesford VIC

    TBH turning on the heater isn't going to have any impact on how the A/C cycles. All that does is adds heat to the air in addition to cool...you have 2 "radiators" in the heater box that the air flows over...one is the evap (cold) and the other is the heater core (cold if you have the heater valve shut, or warm if you have the heater valve open).

    The little thermostat thing (for the A/C dial knob )on the end of the capillary tube is sensing the temperature of one of the A/C pipes as it goes into the evaporator... so it has no idea whether you have the heater valve open or not.

    The thermostat switch has a capillary tube as mentioned and is quite fiddly to remove and install as you have to unwrap the butyl wrap on the A/C pipe and position the capillary tube end...not as simple as unplugging a switch and reinstalling. I definitely have a heater box with the knob and capillary tube still attached...could try to remove it and send it to you...but I'd recommend looking at the coolant charge first.

    Does the A/C blow really cold? I think a symptom of under-charge would be that it just doesn't get really cold, so the capillary tube isn't seeing a cold enough temp to switch off the compressor. unless you have it turned down to a lower setting..my theory anyway. TBH I think you ought to pop down to an A/C place (Maybe Alex Auto that Voldat use??) and get them to check the pressures/charge.

    I'll watch your video and comment further.

  • carnut222Greg S @carnut222 Daylesford VIC

    Further to my comments above, that video is showing significant bubbles in the sight glass, which indicates your system is low on gas, as I theorised above.

  • Thanks for the informative feedback Greg, the system does blow really cold air even with the bubbles.

    I'll see how it goes for a few weeks and then visit a garage to see how pressures are.

    I'll update once I know more

  • carnut222Greg S @carnut222 Daylesford VIC

    Sounds good. I assume when you say it blows cold air, that was prior to the weather getting cold? :)

  • BTW, the 'turn the heater on' idea was to force the thermostat to power on. It sounds now like it is turning on then just not turning off rather than not turning on at all. A different problem that the heater will not help diagnose. Sorry for confusion.

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