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2477Re: a/c starts out cold, then heats up

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  • sheetfar
    Jun 15, 2004
      I have also tested the aux fan (the electric fan located at the very
      front of the car) by shorting the wires for the sensors at the top
      of the radiator per Bentley. Result: The fan works at both speeds.

      I then turned the ignition switch on but didn't start the engine.
      With the ignition on and the A/C switch turned on (the compressor
      clutch engaged), the aux fan then started at low speed. Conclusion:
      The aux fan ain't the problem.

      That leaves the evap temp SENSOR and the evap temperature REGULATOR.

      I removed and tested the temp sensor (it goes inside of the
      evaporator) at room temp and in ice water. Results suggest it isn't

      About the only thing left as far as I can tell is the temp
      regulator. And that would make sense, since the A/C sometimes acted
      up more than at other times. In other words, this regulator would
      probably be more likely to fail with time, since it has a lot more
      electronic devices inside (like those miserable SI boards).


      --- In bmwe28@..., "sheetfar" <sheetfar@w...> wrote:
      > I have a 1986 528e.
      > What would cause the air conditioning to work fine for about 15
      > minutes or so, then start heating up slowly?
      > This occurs under the following conditions:
      > * Air vents closed (no outside air leaking in).
      > * Temp switch set to coldest (rotated CCW).
      > * A/C fan speed set to medium or high (2 or 3).
      > * Outside temp above 90 deg F. (It doesn't seem to act up until
      > outside temp is hot).
      > * Inside air vent (vent above radio) temp starts out at 42 deg F,
      > then slowly works its way up to maybe 55 deg F.
      > What I did so far:
      > * Replaced the expansion valve on the evaporator.
      > The low & high side pressure readings seem ok (20 or so psi low
      > side, and 225 high side. The compressor seems ok, since it cycles
      > off at around 335 psi when the engine revs up. All the gage
      > appear to be normal.
      > The heater control valve is working fine.
      > I heard that the evaporator temp sensor on the earlier models
      > cause icing under certain conditions (Bentley). One parts supplier
      > mentioned the possibility of a bad temp regulator.
      > Any thoughts?
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