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How to blow up your air conditioner

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Jun 24, 2002.

  1. Blue85

    Blue85 Troll Premium Member

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    Just crank it up when it's 95 degrees and muggy WITH NO ENGINE COOLING FAN.

    I've got about 1.5 weeks on the new electric fans and today a connection to a relay decided to give it up. So the condensor had no air flow as I sat in the drive-through line on lunch today. The high temps got the high side pressure up enough to vent the refrigerant out of the pressure relief valve. I thought I had smoke coming out from under the hood! When I looked I realized that it was the gas and saw the oil on the back of the compressor. Then the engine temp was getting up there, but when I stopped again, I pulled the connector off the relay, plugged it back in and both fans started up again.

    It's time to find some more reliable relays. I will also rewire the system so that the compressor can not engage unless there is voltage to the fans and look for a high side cutout switch. A lot of cars come with those. Oh well, I was thinking of changing my orifice tube out anyway.
     
  2. TopOff

    TopOff 1/2 ton status

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    Get the Bosch 30 amp (or larger relays).

    Make sure your wiring is up to it. Atleast 16 gauge, or more depending on the length or wire.

    Still, I would think it would only blow like that if the pressure sides were incorrect.
    I would think the only problem you should have seen were a less affective A/C, and a hotter engine.

    Good luck.
    TO
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    I'd be looking at the crimp connectors. Very prone to corrosion and releasing.
    Bosch makes an excelent relay. I highly recomend them.
    The easy way to wire so you know the Fans have come on is to wire the clutch through the fan relay. What you will have to do is take a trigger wire from the same source as the power going to the fan AFTER the relay. Then use that going to terminal 30 on a Bosch. Terminal 87 to the clutch. The old clutch wire to terminal 85 and Ground to terminal 85. That would make it so that if the fans are not getting power you can't turn on the clutch. Problem is if the failure is the fan then the clutch will still work. The other problem is you will be now pulling power for the Clutch through the fan circuit.
    Heck I'm being stupid! Put the original fan clutch wire to terminal 30. Put the trigger wire from the fans to the 86 terminal. Still get the same effect but the clutch will pull power from it's original source.
     
  4. Blue85

    Blue85 Troll Premium Member

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    Grim,
    This is sort of the same train of thought that I went through yesterday /forums/images/icons/laugh.gif . The clutch (and throttle solenoid) are actually fed by another relay, since my low-side cycling switch has almost 1 Ohm in the contacts now (not enough current for the clutch, but plenty to drive a relay). If the clutch is to only engage when the fans are on, the only way to get a real advantage is to use a sense wire right at the fan motors (after all connections, relays and fuses). However, this will make the clutch engage any time the fans are on to cool the engine ( /forums/images/icons/shocked.gif ) unless an AND function is created (must have fan on AND cycle switch engaged). This requires yet another relay, possibly to give a low side + a high side drive to the clutch relay.

    Instead, I am going to do it the right way and install a high pressure cutout switch. This is more direct control over the condition that I'm trying to prevent anyway. Actually, I've been reading up and it looks like this is a legal requirement for R-134a conversions.

    The system works fine again now with no further charging, so I must not have vented very much. Before I had both fans on a single 30A relay. Each fan draws 10A or less continous and each one still had a good 15A fuse on it. However, the relay socket that I was using seems to have had junk crimps in it. Now I have two new 30A relays, one for each fan and all of the connections are made with new terminls, with all of the crimps soldered. A/C works great today. /forums/images/icons/grin.gif

    At some point I will discharge and change the orifice tube. I still have the GM white tube and I don't think that it gives me low enough low-side pressure on hot days. I will go to a slightly smaller one or I will put in a VOV. I tried a VOV initially and it was a complete plug in the system. I contacted the manufacturer and it seems that I had a dud. You see, I am not one to leave well enough alone if I have a good idea to make something work better!
     
  5. 95 Silverado

    95 Silverado 1/2 ton status

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    you might want to consider using a circuit breaker instead of a fuse for the fan supply voltage. the fan motors pull a surge of current when starting and will sometimes blow a fuse when starting, the circuit breaker reacts slower and will handle the surge without popping. circuit breakers are available that plug in a fuse holder directly replacing a fuse.
     
  6. Blue85

    Blue85 Troll Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    the fan motors pull a surge of current when starting

    [/ QUOTE ]

    Clearly that is the case. For now I am just using slow-blow fuses that are better than half again the steady-state current rating. I ran one of these fans like this all of last summer (as an added pusher on the condensor) without any 15A fuses blown.
     

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