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Air Condition system has a mind of its own ! 700 1991

posted by  chuffsy on  Sun Nov 29 01:57 CST 2009
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last visit: Tue Oct 21 18:17 CST 2014
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Lately the a/c sytem does not turn on right away as it used to ( Compressor does not turn on )...Im in Florida and it is the first time in 9 years of ownership that I am experiencing this problem.I thought it was the pressure sensor on the accumulator ( this went bad before and exhibited not quite the problem I am having now but similar somewhat )so I removed the connector and bridged it and the system still would not turn on...So this is what is happening...I would turn the system on but the compressor would not come on ..drive for about 5-10 mins then it starts to cool and when it does cool it cools well and continues to do so till the car is turned off , then the cycle repeats..Could it be the controller ?








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    Air Condition system has a mind of its own ! 700 1991

    posted by  machine man on  Sun Nov 29 06:07 CST 2009
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    last visit: Wed Oct 22 15:40 CST 2014
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    I'm a 240 man to the bone. 7 series body never won me over then or even used ones today.

    They changed to the lower thinner doors. Guess I’m a tank man.

    Assuming you are not low on refrigerant charge and the compressor is pumping up properly. No leaky valves. A dirty condenser or evaporator issues i.e. leaves and flap doors.

    There maybe a relay!

    On the '86 and I'm not sure about the '91s. Have a delay relay.

    It is in there to stop the compressor from coming on right after disengaging the starter. A 5 second delay is allowed even after the thermostat calls for cooling.

    On my '86 it quit. When that things stops. It did this only once. I removed it on the spot!
    It is gone now. A permanently jumper is in.

    Another brilliant engineer thought that one up. Guess it is supposed to handle excess current away from the ignition switch.

    The pressure switch / thermostat will control the load. It also can be through another relay that could be used.

    The relay has a electronic timing circuit. Yours may be going out of calibration or the connections inside the relay are going south, i.e. solder joints.

    You could try locating it and use a jumper to go around it. Then see if the delay goes away.

    Be glad your car isn’t as fancy as some of those “think for you, talk to you” models. Like automatic climate control. GPS.

    That’s when will find out what you paid for. Like all the goodies are hidden so it looks smooth and nice. Screws and clips are hidden. Then it gets hairy with all those wires in there so tight.

    Then you are really on your own. To what goes on inside those closed up black boxes!
    The less built in, the better.

    Now they have gone to less wire and to buses? Coded signals to each component all on the same bus line. We thought NY and LA had control issues.

    No new cars today. No thanks man.

    On second thought! A robot data bank gadget. To help maintain them would be a nice incentive. You know like in the Cherry 2000 movie!
    The future could get better for us wrench pullers. No longer dull manuals to look at!

    Phil







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    Air Condition system has a mind of its own ! 700 1991

    posted by  someone claiming to be fixit2002 on  Sun Nov 29 02:08 CST 2009 [RELATED]

    Try unplugging the compresor clutch wire where it connects near the compressor. Get a jumper wire and touch it to the positive battery terminal with the engine running and the AC on. The compressor clutch should then engage. If it doesn't then either the clutch is bad or the compressor is not grounded. I believe there's a ground wire that's usually connected to one of the mounting bolts.








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      Air Condition system has a mind of its own ! 700 1991

      posted by  chuffsy on  Sun Nov 29 04:04 CST 2009
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      last visit: Tue Oct 21 18:17 CST 2014
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      I will try that but how do you explain the fact that after a given time the compressor works..I would think that if I had an electrcal connection problem such as a faulty ground it wouldnt work at all but I will certainly try w you recommend. Thanks








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        Air Condition system has a mind of its own ! 700 1991

        posted by  Steve on  Sun Nov 29 12:13 CST 2009
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        last visit: Fri Oct 24 07:16 CST 2014
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        See the FAQ. Within the HVAC controller, the solder joints controlling the current flow to the compressor can fail. Try the diagnostics in the FAQ first, then look at the repair instructions.
        --
        See the 700/900 FAQ at the drop-down menu above right.








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          Air Condition system has a mind of its own ! 700 1991

          posted by  jerryc on  Sat Dec 5 20:42 CST 2009
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          last visit: Wed Oct 8 21:28 CST 2014
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          I just got mine fixed (yeah I know, December, and the air works, cool...) I had tried re-soldering the controller relay but that either didn't last or didn't work at all, I had 3 controllers and tried various things, and I think I can say that just going at it with an iron and some solder is not a reliable fix. The old solder seems to have to be removed completely, like with a solder sucker or the tape stuff that absorbs it. Then new solder and/or new relay.
          It's something I spent a lot of time on and ordered the replacement controller board relay finally. My friend soldered one on, and repaired the solder properly on another. They both work. Bad luck though, the one with the new relay has a vacuum leak in the board. So I'm using the one with the new solder. My friend thinks the old relay was ok. The deal is, supposedly the new relay is rated higher voltage and thus puts less strain on the joint, but he thinks that it's Chinese so likely not as good as the Japanese original relay. I now have 5 controllers and may sell some with the fix if anyone's interested.








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            Air Condition system has a mind of its own ! 700 1991

            posted by  Steve on  Sun Dec 6 01:28 CST 2009
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            last visit: Fri Oct 24 07:16 CST 2014
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            Do you have the specs for the replacement relays? Any soldering tips?
            --
            See the 700/900 FAQ at the drop-down menu above right.








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              Air Condition system has a mind of its own ! 700 1991

              posted by  jerryc on  Sun Dec 6 13:18 CST 2009
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              last visit: Wed Oct 8 21:28 CST 2014
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              Hi Steve
              The relay I learned about in the FAQ, then echoed by Uncle Olaf.

              "Replacement Relay. [Randy Duke] If the solder joints are fine and the relay is malfunctioning, replace it with a Z2570-ND costing about $1 plus a fairly high shipping cost from digikey.com. The old relay is 9V and has a 190 ohm coil resistance, with a current load to the A/C clutch of about 4 amps though the contacts. The replacement relay has a coil resistance of 225 ohms so slightly less current is needed to activate it. The contacts are rated at 10 amps."

              I ordered 3 relays, tripling the cost to $2.91. Shipping, even with triple the weight of about 67 grams, stayed the same. 'grin' Seemed like a wise move.

              Tip on re-soldering is also there,
              "[Response: Brian Oliver]...Use a desoldering braid to remove excess solder."

              We found removing the old solder completely with this braid, which works by wicking the solder away and is very inexpensive, and then using new quality solder was the way to go. I did not want to spring for a solder sucker, which vacuums the melted solder as you work and runs around $40. As I said above, not removing the old solder but just reflowing it, is not really worth doing. I must have done that 4 different times on the various controllers I acquired.
              My friend said it took an hour to r&r the relay, about 20 mins to replace the solder. This is after the controller is out and on the bench. He's good at that stuff, it's not really my province so only repeating what he told me.
              Hope this helps someone.







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