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Thread: Air con wiring advice needed?

  1. 5th September 2011, 08:12 PM #51
    isuzu110's Avatar
    isuzu110
    isuzu110 is offline Master Supporter
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    Here's a wiring diagram from elsewhere on this site





    It shows only one pressure switch between the thermo amp and the clutch. I can see a pressure switch on top of the receiver-dryer and that has no power to it, even though the wire feeding it from the thermo amp is live. Has anyone seen a second pressure switch in series in the circuit or a relay between the thermo amp and receiver-dryer pressure switch ?
    '95 110 300TDI, F&R ARB Lockers, Twine Shower, Aux Sill Tank, Snorkel, Cargo barrier, 9 seats, swingaway wheel carrier, MadMan EMS2
    '85 110 Isuzu NA 4BE1 3.6l Diesel, 0.996 LT-95, Rear Maxi (SOLD)
    '76 SIII 109" Nissan ED33 5-SP Nissan GBox (SOLD)
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  2. 5th September 2011, 08:25 PM #52
    Ratel10mm
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    Ok, it looks to me as though the double rectangle shape on the cable from the thermo-amp to the pressure switch designates a plugor other connector. If you have a signal leaving the thermo-amp but nothing at the feed to the pressure switch, then the first thing to check is that connector.
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  3. 5th September 2011, 08:42 PM #53
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    isuzu110
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    Yes - I've already checked the connector and no power.

    Next thing is to run a new wire from the thermo amp to the receiver dryer pressure switch and hope I bypass the problem. Hopefully I'm not bypassing another hidden hi/lo pressure switch and there's just the one of them.
    '95 110 300TDI, F&R ARB Lockers, Twine Shower, Aux Sill Tank, Snorkel, Cargo barrier, 9 seats, swingaway wheel carrier, MadMan EMS2
    '85 110 Isuzu NA 4BE1 3.6l Diesel, 0.996 LT-95, Rear Maxi (SOLD)
    '76 SIII 109" Nissan ED33 5-SP Nissan GBox (SOLD)
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  4. 7th September 2011, 09:19 PM #54
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    isuzu110
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    Ok, I think I have this one...

    Looks like the output relay on the thermo-amp circuit board is dodgy. The relay clicks OK, but the contact doesn't make properly- hence intermittent voltage to the pressure switch and compressor clutch. If you tap the relay when it is energised, the contact finally makes. I suppose this relay has cycled many times since the vehicle was made in 1985.

    The thermo-amp manufacturer Genelco seems to have been bought out by another US company Arizona Instruments in the late 80s. AZIC don't seem to manufacture the thermo-amp any longer.

    The relay is manufactured by Sky Electronics in Georgia, but I am yet to find an Australian distributor for them. The pin-out of the relay (CKC-1C) seems somewhat unique to this manufacturer.

    I may need to remotely mount a replacement relay off the PC board.
    '95 110 300TDI, F&R ARB Lockers, Twine Shower, Aux Sill Tank, Snorkel, Cargo barrier, 9 seats, swingaway wheel carrier, MadMan EMS2
    '85 110 Isuzu NA 4BE1 3.6l Diesel, 0.996 LT-95, Rear Maxi (SOLD)
    '76 SIII 109" Nissan ED33 5-SP Nissan GBox (SOLD)
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  5. 8th September 2011, 07:11 PM #55
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    isuzu110
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    Yeah guys, sorry if this bores you....

    If your 300tdi Defender aircon stops working after a few minutes even though it's all gassed up, check the blue relay inside the thermoamp box is actually switching despite making a clicking noise. I suspect the contact rating may be marginal for the application. A simple way for me to test this was tapping the thermoamp box and hearing the compressor clutch kick in.

    The specs for the orginal relay are here http://www.sourceresearch.com/sky/sk...dfPage=CKC.pdf

    I've removed the offending relay from the printed curcuit board on the thermo amp. I was hard pressed finding a replacement that only had a coil current draw of 30mA and was worried a relay with a larger coil current may have damaged the driving transistors.

    I ended up going a bit overkill and buying a kit from Jaycar DC Relay Switch Kit - Jaycar Electronics that draws a very low current and is opto isolated from the switching thermoamp. The relay is rated at 30A - way overkill.

    All good so far.
    '95 110 300TDI, F&R ARB Lockers, Twine Shower, Aux Sill Tank, Snorkel, Cargo barrier, 9 seats, swingaway wheel carrier, MadMan EMS2
    '85 110 Isuzu NA 4BE1 3.6l Diesel, 0.996 LT-95, Rear Maxi (SOLD)
    '76 SIII 109" Nissan ED33 5-SP Nissan GBox (SOLD)
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  6. 8th September 2011, 08:04 PM #56
    Ratel10mm
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    Good news. Congrat's on the fix.
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  7. 9th September 2011, 05:29 PM #57
    Davehoos Guest
    common fault over time.also cracked older joints.

    sometimes its can be caused by the current draw on the clutch coil.
    normally these draw 2-3 amps.when hot it can go up to 5 amp and when the fan starts to draw current the voltage drops raising the current needed to pull in the clutch coil.

    the power is supplied to the clutch from the same fuse as the blower fan.
    you can electrically melt the clutch coil before the fuse blows.

    worth fitting a 7.5-10 amp quick blow [spade] fuse to the circuit before or after the pressure switch or a relay with fusedirectly from battery 12 volts. .
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