European 98 Mazda 626 2L GF

The AC stopped working recently ( no cooling at all, measured at central vent ). When I turn on the AC the clutch engages and seems to stay engaged. The clutch does NOT seem to be clicking on and off. However there is a rapid ticking noise coming from the compressor at idle. It's very similar to the noise in this video, Ticking AC Compressor.

Checking the tubes to and from the dryer / receiver they both seem to be ambient temp after running the engine at about 1800 rpm for five minutes. The tubes from the evaporator also seem to both be ambient temp. The sight glass in the dryer seems to be clear with no bubbles.

There is a four wire sensor in the dryer / receiver. With the AC off the wires read 14.1v,13.7, 13.7, 0 and with the AC on 14, 0.16, 0.16, 0.

With the clutch seemingly staying engaged and that rapid ticking noise from the compressor plus no cooling I'm guessing the compressor is shot but I'd like to hear from someone with more AC experience than me.

  • You checked your pressures, low and high side? Feb 17 '19 at 13:53
  • @Pᴀᴜʟsᴛᴇʀ2 I don't own a set of gauges, I'm assuming since the clutch is staying engaged that means there is sufficient gas in the system... Feb 17 '19 at 14:13
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    I was actually wondering if you'd see the pressure differential between high/low sides. Sitting still over time, the AC system will equalize. When the compressor is engaged, you'll get the pressure differential between the two sides. This will tell you if your compressor is working or not, and at what efficiency. Feb 17 '19 at 14:33

So just to follow up for anyone interested. It turns out there was no pressure or gas in the cooling system. We refilled it and the noise went away. With the AC on low side was about 49 PSI and high side about 125 PSI. Central vent went from 72.6 F* down to 44 F* with AC on.

The four wire sensor on the dryer showed 14, 0.46, 0.46, 0 with the AC on as opposed to 14, 0.16, 0.16, 0 when it was on and empty.

Quite frankly I'm a bit confused as to why the sensor didn't disable the compressor clutch when the system was empty of gas and exactly what that sensor's job in the system actually is.

  • Did you perchance hear any loud hissing noise from inside the car (vents, footwell are the locations) while you ran the AC? By the way the loud ticking is a scroll/vane compressor running with not enough lubrication (the refrigerant is what brings lubricant to the compressor and with low refrigerant most of the oil stops inside the evaporator). What compressor model do you have?
    – Al_
    Feb 22 '19 at 12:08
  • Also, another question. Can you smell anything resembling fresh paint from the vents especially right after you turn the blower on? If so you may have an evaporator leak. That's the smell of PAG compressor oil.
    – Al_
    Feb 22 '19 at 12:20

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