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308 A/C temp control probe

Discussion in 'Technical Q&A' started by ria, Nov 16, 2003.

  1. ria

    ria Formula Junior

    Nov 2, 2003
    725
    ohio
    Full Name:
    phill
    can anybody tell me where the temp control probe goes in to for the a/c. the switch is located at the senter consol it has a long steal wire to control the a/c temp. wen i got my car this wire was cut off by the switch and missing now i got a new switch but i DONT KNOW where the probe goes in TO!!!!!! this is a 1980 308gtsi any info on this!!! thanks.
     
  2. DGS

    DGS Three Time F1 World Champ
    Rossa Subscribed

    May 27, 2003
    34,181
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    DGS
    That's not a steel wire, it's an aluminum capillary tube, filled with ammonia. The aircon temp "switch" is a thermostat, using the capillary tube to remotely probe the temperature of the evaporator (the thing that gets cold in the aircon). It needs to probe the evaporator, to make sure it doesn't ice up.

    The capillary tube runs under the center console, up to the front, and then up to the aircon evaporator located, if the 308 is like the 328, under the pass side dash board (up near the forward wall). You have to pull out most of the center console to route it up where it goes.

    These same remote sensing thermostats are used in Coke machines. (I found the one that was in my 328 on G.E. Industrial's web page -- listed as being for a "drinks dispenser machine". )

    I've been playing with an op-amp circuit to replace it, to use a Radio Shack thermistor instead, to save having to route that long tube under the console. (Using connectorized wires, instead of an attached capillary tube.). I've got a breadboard design sitting on my desk, but I'm still dithering whether to make it "plug replaceable" with the original, or to locate the circuit board to the evaporator. (The center console in a GTS in direct sunlight gets pretty warm, even for mil-spec circuits.)
     
  3. ria

    ria Formula Junior

    Nov 2, 2003
    725
    ohio
    Full Name:
    phill
    i want to thank you for the info.
     
  4. Paul_308

    Paul_308 Formula 3
    Silver Subscribed

    Mar 12, 2004
    2,335
    It goes forward ending in the spare tire area at the a/c filter.

    Heresy - you don't need it. If the a/c were super good, you could set the temp control and the system would cycle on/off holding a specific temperature inside the car. Unfortunately, the a/c isn't that effective, the switch needs to be on at all times with the only exception being lower than 15c outside when the system can ice up with the a/c on. Make certain the switch turns on to activate the compressor clutch and drive away.
     
  5. DGS

    DGS Three Time F1 World Champ
    Rossa Subscribed

    May 27, 2003
    34,181
    MidTN
    Full Name:
    DGS
    I can't say for a 308 converted to "new" refrigerant, but my 328 with R-12 was blowing 0C air in August at ambient temps in the 80s (28-30C), with the thermostat bypassed (manually switched). (I ran a digital thermometer probe into the center aircon vent to monitor the workaround.)

    You can run it in "always on" mode, if you keep an eye on the evaporator temp -- which is a pain when driving.

    Ideally, an aircon system should monitor the evaporator to prevent icing, and monitor the cabin temperature for automatic climate control. The long capillary tube is a compromise, probing the temperature at the evaporator, but also heated by cabin temperature on the way back to the console. If the console was parked in direct sunlight (GTS top off), even a frozen evaporator isn't going to switch off the thermostat sitting in a 44C (112F) console. (The digital thermometer I put on the aircon system was a dual reading type, sitting at the console.)

    (I guess this is about time for this thread to come back ... even if we did get nine inches of snow, last night.) ;)
     

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