Troubleshooting A/C clutch refusing to engage.

Discussion in 'Volvo Forum' started by Joeziah, Mar 3, 2023.

  1. Joeziah

    Joeziah Light Load Member

    Jan 2, 2016
    Truck is a 2008 VT880 - Truck was repowered so the general setup is ... out of the ordinary non the less it should be strait forward for the A/C

    Problem - Clutch won't engage on the compressor, first I though ohno...system isn't charged and leaking so I hook up my manifolds and find the low side sitting around 70 and high side at 110. Pretty normal for not being on.... I think.

    I test for power to the clutch, no voltage (truck running, fans on high, a/c ON, thermostat all the way to cold (although this has never actually worked it either freezes you or its off since the repower)

    Ok, what could do that? Fuse? Only fuse I see is for the entire climate control module and it is fine.

    Ok, pressure switch then? I don't know how to troubleshoot this and need help.

    I assume the circuit is complete, unless the pressure is out of spec and then it breaks the circuit.

    Ok so I check continuity on the high pressure sensor, it is in fact completing the circuit.

    Ok, so low pressure? 3 wires? what?!

    I'm guessing the red wire, which has 5v running to it, is the common, the other two must be a high pressure and low pressure trigger, meaning they all need to have continuity to function and send the ok to engage the clutch? Pressure too high and breaks circuit, too low and breaks.

    I am getting zero continuity between any combinations of any of the nodes on the pressure switch. So either its functioning like it should and its reversed from what I think, as in if it does get voltage back from that switch it knows to shut down the compressor?

    Ok, so I put a jumper between all 3 wires...hopefully it doesn't damage anything....A/C clutch still not getting power.....

    I tested the compressor by manually running power to it from a battery, it engages and I get the low side down to around 30psi and high side to 110/120 (with blower fans on high and engine fan on)

    It only pulls 1 amp at the clutch when doing this so i think the compressor is fine and doing its job.

    Ambient temp is 45ish degrees currently.

    What is next here?

    Wish I could upload images or embed but its never worked on this forum...


    All assistance is appreciated.
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