We had our first really warm day of summer and my Diesel S-type had to tough it up outside. When I got to it the a/c is blowing out hot air and making a continuous hissing noise from the dash. If I turn the compressor off the hissing stops. According to the laptop the drover and passenger temperatures are 31 degrees c on full cold and rise on full hot before dropping back to 32 on full cold so I reckong its not the heater valve especially as the engine was relatively cold when I first. notced the fault. Static pressure with compressor off in the a/c is reported as 75psi and its round about 125psi with the compressor on. Both pipes under the hood are a similar temperature.
is this symptoms of a low charge or something more sinister?

 

Hissing sound is not uncommon in a low a/c gas situation. Don't assume worse, and get gas a/c gas checked.

 

Sadly when I moved the car it left behind a pool of oily a/c dye, further investigation shows an oily dye patch on the left side undertray from just forward of the left wheel. The gauge port that's in that area is dry so it looks like the in car bit or a pipe connecting it has failed spectacularly. Curiously enough the condensate drain doesn't have any dye on it which I thought it would have if the in car evaporator would have failed.

Does anyone have a clue what's happened? A week ago it was on a hoist to have the gearbox checked for leaks and they didn't mention anything. It's a long shot but could the hoist have crushed a pipe?

 

Could be a relief valve gave way due to high system pressure?

Sorry, I don't know the mechanical layout on the diesel.

 

Ah,


Not sure, but would imagine is similar layout to the Petrol units. Engine bay has a long pipe that runs full length from left to right, behind engine. Had pipe go on my V8 last year, fluid loss was minimal, and it took quite a few months before most of the Gas/Oil had leaked out. Like you sign was a small amount of dye on Garage floor. Had to replace whole Pipe as it had split on seam....., and was not worth patching. Split was on pipe running width of Bulkhead, but because of undertray, appeared near left hand front wheel.

 

Further update on this, after getting it up on a hoist and having the splash guard removed I discovered the condenser to compressor pipe has rubbed though and as I parked it on a slope it ran from front to back. As it seems the line is combined with the feed from the compressor to the cabin I'm going to see if I can go the cut out a bit of pipe and replace it with a compression fitting and a flexible hose route. I'm also replacing the condenser as it has a slow oily leak in one corner courtesy of salt corrosion and proven by a UV light and dye. This isn't expected to arrive until January and I'll update this thread with the fix.