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Thread: a/c blows cold but.....

  1. #1

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    a/c blows cold but.....

    I have to hot wire clutch. So no 12v to clutch, Freon is all in check so good there and I'm getting 12v at the relay, but only 2.7 volts to the low pressure switch. I also checked volts at the a/c switch connecter on dash, nothin. Anyway to check the a/c module, that's the black box under evap case right? I heard there a bit delicate? It's kind of funny, I found a trail of evidence where the last technition hunted on the same path as me, but broke every little plastic tap/clip along the way.... Any other ideas

  2. #2

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    You should have 12 volts at the a/c switch on the dash. The 12 volts comes from the blower switch. Did you check for power with the blower motor on?

  3. #3

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    Quote Originally Posted by crvtec90 View Post
    You should have 12 volts at the a/c switch on the dash. The 12 volts comes from the blower switch. Did you check for power with the blower motor on?
    Okay, I do have 13 volts at the a/c switch and 12v at the controller (black box under evap case) from thermister

  4. #4



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    You must have a bad connection with lots of dirt or oil on somthing. I think we have a manual with the electrical system on your truck. In the manual; section under 216 manuals. look for the pick up and montero book. I think there is one in it.

    Do you have 12V on both sides of the AC button?
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  5. #5

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    Quote Originally Posted by camoit View Post
    You must have a bad connection with lots of dirt or oil on somthing. I think we have a manual with the electrical system on your truck. In the manual; section under 216 manuals. look for the pick up and montero book. I think there is one in it.

    Do you have 12V on both sides of the AC button?
    Only one wire going to the switch has the 13v. My Haynes book only goes up to 93' (wiring is a bit different than what's in my car) but I just bought a factory manual that goes up to 96' ....so hopefully that will help some.

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    There should be a relay between the Thermostat and the clutch. Look there for the voltage drop.
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  7. #7

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    yes the voltage drop is there, 1 terminal has 14.4ish when running and a/c switch on and the terminal from the low pressure switch & coolant temp sensor (black w/yello strip) has 2.7 v

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    OK now you need to fallow the low voltage back to where it goes back up. There you will find the problem. There should be no drop in the system.
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  9. #9

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    Well I did some checking today, the wire with the 2.7 volts (according to my 93' Haynes manual) travels to the a/c thermostat (but my truck is a 95') so my truck has a MD630306 controller. So I'm thinking this is where the problem lies. Can't wait to get the new manual..any thoughts on "that" black box?

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    sent you a PM with link to manuals you can use.
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  11. #11

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    Received my manual today...WOW, this thing is awesome, a lot better than the Haynes...anyway I found the problem, it's in the black a/c controller, if I jump the 12v (blue w/red stripe) to the 2.7 v (black w/yellow stripe) at the controller (unhooked) the compressor clutch works as it should, complete control with blower switch and a/c switch. I guess what doesn't work is the thermostat area of the unit. Anyone with a black box they'll sell?
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  12. #12



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    Can you scan in your manual to PDF? If so then you can send it to me and I can drop it on the board for everyone. Only if you want to. The bad thing is you need to cut the book up so you can run it through the scanner. It took me about 4 hours to do my first gen manual.
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  13. #13

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    Im not sure exactly how your HVAC wiring is laid out but usually there is the high side pressure switch and the low side pressure switch between the pcm and the relay. they are normally closed circuits so if pressure gets too high on either side it will open the circuit, there by cutting power to the relay. So in other words you may have a short in your pcm or one of your pressure switches is faulty. But again, i dont know how it is on an older truck.

  14. #14

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    Im not sure exactly how your HVAC wiring is laid out but usually there is the high side pressure switch and the low side pressure switch between the pcm and the relay. they are normally closed circuits so if pressure gets too high on either side it will open the circuit, there by cutting power to the relay. So in other words you may have a short in your pcm or one of your pressure switches is faulty. Also it may be your Ambient Temperature sensor. But again, i dont know how it is on an older truck.

  15. #15

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    Quote Originally Posted by DOPRIUS View Post
    Im not sure exactly how your HVAC wiring is laid out but usually there is the high side pressure switch and the low side pressure switch between the pcm and the relay. they are normally closed circuits so if pressure gets too high on either side it will open the circuit, there by cutting power to the relay. So in other words you may have a short in your pcm or one of your pressure switches is faulty. Also it may be your Ambient Temperature sensor. But again, i dont know how it is on an older truck.
    It has a dual pressure switch, which I jumped...didn't make a difference?

  16. #16

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    Whats the volts to the first pressure switch?

  17. #17

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    it only has one switch, a dual pressure....2.7 volts

  18. #18

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    The dual pressure switch on the lower left side
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  19. #19

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    Sounds like a short in your pcm. Or you may have a bad relay.nhaveyou checked the relay?

  20. #20

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    Jump 12v across the relay to the press. switch and see if your gettin 12v

  21. #21

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    Quote Originally Posted by DOPRIUS View Post
    Sounds like a short in your pcm. Or you may have a bad relay.nhaveyou checked the relay?
    Well I'm getting 12v at the relay, also I'm getting 2.7 volts at the relay (all with the relay disconnected) So my thinking is it's not the relay if I'm getting 2.7 volts there without it being connected. Short in the PCM? It does connect to the other side of the low pressure switch, but the 2.7v is comming from the controller side of the a/c circuit not the PCM....Please correct me if I'm wrong?

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