09 prostar a/c replaced everything still not working

Discussion in 'International Forum' started by radicastuff, Aug 7, 2012.

  1. NealBoat

    NealBoat Bobtail Member

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  3. Heavyd

    Heavyd Road Train Member

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    There is air switch the body controller uses for an input for the brake lights. This switch is located in the dash above the brake pedal. I would try to change this first. These switches do fail after time. The relay you are hearing is for your trailer stop lights. If you have no trailer and no truck brake lights, the brake switch is the first to change. The brake switch input to the body controller can all be monitored through Diamond Logic software if the shop has it. This way they can verify where the loss of the signal is happening. The brake switch is also a "smart" switch in that a small voltage trickles through it all the time so the body controller can "see" that it is there and the circuit is ok. When you hit the brakes the voltage signal changes and body controller will turn on the brake light output circuits. With the TC light coming on is another indication that the brake circuit is in an invalid state and probably logging a "brake switch stuck" code.
     
  4. A21CAV

    A21CAV Road Train Member

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    Heavyd, do the preceding diagnostic tips apply to a 2011 Prostar with the ISX 400 that has a June, 2010 build date?
     
  5. Heavyd

    Heavyd Road Train Member

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    Yes they do!
     
    A21CAV Thanks this.
  6. niterngr

    niterngr Bobtail Member

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    Have them replace the thermasters that is problem had the same thing happened to 3 of them and that was the cure
     
  7. texasmorrell

    texasmorrell Medium Load Member

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    I've got a new problem now. I replaced all three sensors on my AC system last month. It was working great until today. It started doing the same thing it was doing before. It will be cold for 15 minutes and then it will get warm again. That's the body controller trying to protect the system from damage. But this time when it stops being cold I check the AC compressor and the clutch is engaged and the AC compressor is turning. This does not make any sense. If the AC compressor clutch is engaged I should be getting cold air. When I cycled the ignition I get cold air again for a little while. I started playing around with the control and realized even if I selected defrost for example the AC compressor still remains engaged. The only way to get the AC compressor clutch to disengage is by turning the fan control all the way to off. If you turn the fan on at all the AC clutch engages again no matter what you have selected on the third dial. Whether it's Max AC or defrost. So I don't understand why it will be cold for 15 or 20 minutes and then start to warm up but the AC clutch remains engaged and the compressor is turning. The body controller is not shutting off the AC compressor. That is easy to see. I'm guessing it's the control head in the dash. What do you guys think?
     
  8. texasmorrell

    texasmorrell Medium Load Member

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    Does anyone know how to calibrate the HVAC controls on the ProStar? I used to know how to do it but I forgot. I know it involves turning the fan control switch all the way to high and selecting Max AC on the selector switch. You're supposed to turn the ignition key to the right without starting the engine and you're supposed to pull a certain fuse. If you do this in proper order it will start the calibration sequence. Does anyone remember the exact way to do this?
     
  9. Heavyd

    Heavyd Road Train Member

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    The easiest way is to remove the HVAC breaker for 30 seconds and plug it back in. Leave the key on with nothing else. Once you plug the breaker back in the HVAC module will self calibrate all the door actuators. If you listen you can hear them.

    As for the problem, it could be a bad HVAC control unit. The next time the a/c gets warm, grab the a/c lines at the firewall going into the blower box. They should be nice and cold. If they are, I suspect a temp blend door problem. To confirm this you would need to pinch off on of the heater hoses going to blower box to stop the flow of hot engine coolant.
     
    QUALITYTRUCK Thanks this.
  10. texasmorrell

    texasmorrell Medium Load Member

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    Thanks HeavyD. I hope its not the blendoor. I just had that replaced last month because it had a crack on the part that actuates the door.
     
  11. 2011Pro Star

    2011Pro Star Bobtail Member

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    Sep 28, 2014
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    Where is pressure switch on a 2011 pro star. Is it the one on top of radiator/condinser. My fan doesnt come on with ac
     
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