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AC question, early 240 200 1983

posted by  wolf_walker on  Sun May 25 17:00 CST 2008
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last visit: Sat Aug 11 19:29 CST 2012
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Gave the AC a preliminary glance while I was installing a radio today.
The microswitch on the knob was cracked and falling apart, and the switch itself felt funny, I replaced it with one from my parts car, wrapping the brass wire around the expansion valve, or that area anyway.

I jumped the pressure switch on the drier, no comp, I applied 12v to the comp lead, it came on. Is the comp directly powered through that pressure swtich?
I didn't have time to trace it out today.

So, that switch. I gather clockwise and in the red is supposed to be full cooling, in the blue is adjustable temp, comp cycles on and off at varying rates.
What does that microswitch do though? I observed that the blower fan actually turned off, totally, when the switch was full counter clockwise and the microswitch was clicked. I also observed the car idled even worse than usual in this position, what felt like a dead miss at idle. I was out of diagnostic time, and I'm sure the system is low, and still R12.

What is the deal with the full CCW and bad idle?







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    AC question, early 240 200 1983

    posted by  bluedot on  Mon May 26 01:08 CST 2008
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    last visit: Mon Nov 15 07:05 CST 2010
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    The microswitch engages a relay that operates the blower on low.This ensures airflow over the cold evaporator.
    Bill








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      AC question, early 240 200 1983

      posted by  wolf_walker on  Mon May 26 11:15 CST 2008
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      last visit: Sat Aug 11 19:29 CST 2012
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      So full CCW is off, as in NOT on the low speed, and anything past full CCW is the reason the fan never turns off?

      I'm still puzzled why it idles worse when at full CCW. Unless when at anything OTHER than full CCW the AC idle adjust is activated, and it idles better with it enabled. I wouldn't be surprised of this, car needs an engine harness and a lot of tuning.







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    AC question, early 240 200 1983

    posted by  B.C. on  Sun May 25 18:07 CST 2008
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    last visit: Wed Mar 28 22:28 CST 2012
    [RELATED]

    Yes, the pressure switch atop the receiver/dryer is in the line to power the compressor clutch. Low pressure (meaning low charge) trips switch and clutch is disengaged.

    Jumping is OK for short periods. Long periods can damage the compressor as some of its lubrication is via the oil suspended in the refrigerant.

    When the clutch is engaged, a solenoid, usually mounted on the firewall, is also engaged and it adjusts the idle speed by allowing a little air in. This is to compensate for the load from the compressor. If the engine idles better with the solenoid engaged, the "normal" idle is incorrect. I believe that the solenoid can engage independent of the clutch.

    At full CCW position, the A/C system is off. Turning the knob towards the red mark moves a setting to be colder and colder. The red mark is a warning to not leave the knob in that position long to avoid icing up the evaporator.

    You mention wrapping a brass wire around the expansion valve, or thereabouts. If it is a wire, not a 1/8-inch tube, it's not like 240 a/c with which I am familiar. If it is actually a tube, it must be filled with Freon in order for the thermostat switch and expansion valve to work properly.

    I don't know if this helps. With a little luch another BB'er will chime in with more and/or better answers.

    Good Luck,

    Bob

    :>)







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