Thread: Aircon problems D2

Originally Posted by rick130

The high pressure cut out point is worse than extreme, no system running R134a should ever be allowed to reach those sort of cut out pressures.

91*C condensing temperature in refrigeration/air conditioning is insane. In a saturated environment (one where we have a liquid and vapour present together) there is a definite pressure/temperature relationship.
A pressure of 464psi with R134a=91*C (sorry for the mixed units)

To give you an idea of what I mean, in commercial refrigeration using R134a we set the HP cutout to around 200-220psi/1400-1540kpa gauge.
That's a safety limit, not working pressures.


Unfortunately 190-200psi is a normal working pressure in car/bus/truck/tractor a/c here, so the HP cut out is set higher, and I'm pulling numbers out of my arse here, but I wouldn't go higher than 260psi gauge, but IIRC most car systems were set to around 290-300psi. 260psi gauge is 65*C condensing pressure. That's considered extreme temps/pressures with that refrigerant.
That's where industry pressure/temperature charts max out. They don't go any higher.

464psi gauge pressure is bonkers, it's equal to 91* condensing pressure. The temperature at the discharge valves where the refrigerant is a superheated vapour, not a saturated vapour, it will be considerably higher, I'm guessing in excess of 50* higher, maybe more.

Refrigeration/air conditioning systems aren't designed for those temps, 65* saturated temps are considered extreme and the point where components start to fail.
I'm agog that Land Rover would use an HP limit so high.

And use a low pressure cut out on the high side of the system?

I have seen this before,but not good industry practise.

Oh,and as said,those pressure switch figures are out of my genuine LR set of workshop manuals for the D2.

As for 404a,we set all HP settings on 400PSI,or we have dramas,particularly out Ipswich way,where ambient temps are often 42 degrees for a few weeks each year.

Then again,we had a 10HP Hitachi ducted with no pressure switches at all,they rely on the compresser overheat thermistor to stop the compresser.Well that didn't take long to burn out the compresser,and no doubt fill the system with moisture and air

Does anyone have the pressure switch settings for the D3/4?