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Car with relay issue, compressor works fine

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  • Car with relay issue, compressor works fine

    Hello all. First post here. I realize this is a general issue. I have an '04 Chrysler Sebring 2.4 Sedan that I cannot get the AC to run. I ran a circuit tester from battery to compressor plugin interface and got a negative light. I found the compressor relay in the fuse box and removed the relay, put a paper clip in to get the compressor clutch to engage/disengage. I turned on the engine and A/C full blast and when engaging the paper clip in the relay interface was able to get cold air to blow and my thermometer reflected the temp dropping rapidly. So I figured bad relay, right? Went to parts store and bought relay. Put in fuse box, turned on AC, still warm air and compressor not engaged. Went to another store just on chance relay was not good and got same results. I verified the compressor is OK and got cold air once manually engaging with the paper clip. But I stick in new relays and STILL doesn't work? Why could this be? BTW I did have a manifold set and a can of R134a attached; it never pushed any (I don't think it did) into the system since the compressor wasn't activated. When it was activated manually it still didn't push any in. I took it off and still got the compressor to push cold through when using the paper clip.

  • #2
    A relay is just that, it "relays" the signal it get from somewhere else down the line to something else. In this way a low current can control a larger current.
    What this is telling me is that the signal to the relay is not turning on the system.
    There are a few things that must be satisfied for the system to turn on. How they are measured and controlled can differ from year to year and mfg to mfg.
    1st there is a low refrigerant cut-out that prevents the system from running when low to prevent burning up of the compressor. Next there is some sort of temp control to prevent the evaporator from falling below freezing and icing over.
    These signals can be as simple as a snap-action switch somewhere in the system, or as complex as a pressure signal read by a climate ECM that controls the relay.
    Jumping ECM controlled circuits is an easy way to cause expensive problems. ECM's often use a 5 volt (max) signal voltage that the ECM runs though a logic circuit to decide if it should turn the compressor on or not.
    In either case, the relay is just a remote controlled switch, after 2 replacements you can be fairly sure that is not your problem.
    You can continue to throw parts at it, and the next two parts to try would be a low pressure switch and "frost switch" if the system has these parts, or a pressure transducer if that's what it uses. These parts can be hard to get to (esp if the system uses a frost switch or transducer in the evaporator). The other alternative is to get the service manual for the car and follow the diagnostic chart or take the vehicle to someone (dealer or independent) shop that has this info.
    Jumper wiring can burn up electronics (esp if the control is in the main ecm) that can cost more than the car is worth to repair! Be warned.
    I am not too concerned with pressures at this point, but both static and operation pressure readings along with temp readings will be required once the compressor is operating to asses the system.


    • #3
      a quick look on Rock-Auto for your year and model brings up several parts, A temp transducer, a pressure transducer, a trinary switch and HPCO.
      I think you will be money ahead to pay someone to repair, these are no longer simple systems.
      Some, like the HPCO require emptying the system of refrigerant to replace the cut-out on the compressor.
      Last edited by Cornbinder89; 04-27-2019, 12:53 PM.


      • #4
        Thank you for helping me with your inputs.