AC pressure switch failure?

[vnx205]

Is it possible or even common for the AC pressure switch to fail on the 300Tdi?
The AC wasn't working when I bought the vehicle, so I had it tested for leaks and regassed. They did a pretty thorough job of checking, but couldn't find a leak anywhere.
It worked well in the NT for a couple of months but a month or so later I noticed it wasn't working. The blower fan and the radiator fan start, but the compressor doesn't click in.
I tried momentarily bypassing the pressure switch near the receiver/drier (or whatever it's called) and the compressor worked. There was some sign of bubbles in the sight glass, but not a lot.
So is it most likely to be a leak that was not detected or a faulty switch?

[ladas]

Is it possible or even common for the AC pressure switch to fail on the 300Tdi?
The AC wasn't working when I bought the vehicle, so I had it tested for leaks and regassed. They did a pretty thorough job of checking, but couldn't find a leak anywhere.
It worked well in the NT for a couple of months but a month or so later I noticed it wasn't working. The blower fan and the radiator fan start, but the compressor doesn't click in.
I tried momentarily bypassing the pressure switch near the receiver/drier (or whatever it's called) and the compressor worked. There was some sign of bubbles in the sight glass, but not a lot.
So is it most likely to be a leak that was not detected or a faulty switch?

It is possible, but not that common.

It's more likely to be a loss of refrigerant (which is all too common)

However there are quite a few other things it could be as well, but my bet is you have leaked gas. Sometimes very difficult to trace, and if it worked for a month before quiting the leak would be very small.

I use flourescent leak dye and a ultra violet lamp to test for leaks - that shows up even the minute leak.

If you haven't got gauges it's difficult, but not impossible to test.

By pass the press switch, start the car and the air con.

After a few mins do a test feel on the following pipes

Small paipe on the compressor (careful this might be hot) should be too hot to hold onto for any lenght of time

The large pipe onto the compressor this should be cool, getting cooler.

trace the small pipe from the compressor to the condenser, then find the pipe comming out of the condenser, this should be warm (warmer than ambient air) but not hot,

Then find where the two pipes go through the fire wall, the larger pipe should be quite cold.

If the small pipe on the compressor is not that hot, the pipe comming from the condenser is ambient temp and the big pipe coming through the firewall is not that cold, then you are most likely to be short of gas.

If the small pipe on the compressor is hot, the pipe from the condenser is warm, but the big pipe from the firewall is not cold then the TX valve is faulty or the filter drier is blocked.

To test to see if the filter drier is blocked (Black canister looking item about the size of a large beer can) - trace the warm pipe from the condenser to the filter drier. Feel the heat of that pipe, then feel the heat from the pipe leaving the filter drier, if the temp is vastly different then there is a blockage (pressure drop through the drier and press = temp)

But my bet is it is a leak.

[vnx205]

Thanks for very detailed info. Filter drier was replaced as part of the regas. The testing for leaks was done with a probe. Is the fluorescent dye a better test? Is it commonly used?
Will run all those checks and see what I can discover.

[ladas]

Thanks for very detailed info. Filter drier was replaced as part of the regas. The testing for leaks was done with a probe. Is the fluorescent dye a better test? Is it commonly used?
Will run all those checks and see what I can discover.

The probe leak tester are very unreliable - especially in a car engine bay where you have quite a lot of air from the fan moving around, it's hot, and there are other fumes, oil fuel etc.,

On most current cars the dye is added at the factory, and it is much more reliable.

[UncleHo]

G'day vnx205 :)

I would suggest that you try to twist the hoses at the hose/pipe joints, that is where we found the SLOW leak in the Dunnydore's A/c :( the hose joint/s have failed.

cheers