XJ40 1990 air conditioning system:
The manual states that there is a 3-stage pressure switch.
I only find one sensor that sits on the back of the compressor (two wires).
this is probably the minimum pressure switch.
Where is the high pressure switch that switches off the compressor in the event of excess pressure and switches on the additional fan on the condenser?
Thank you
This sensor in the compressor It’s the thermal switch, it turns off the compressor from overheating. Fan is activated by a temperature sensor in the bottom of the cooler at 95*C
thanks for the information.
where are the air conditioning pressure switches?
the additional fan only comes on when the water temperature is increased and not when the air conditioning is switched on for the condenser?
ad1 they are not there 
ad2 yes
I don’t really think so …
would be the first air conditioning system that works without a pressure switch (compressor protection)
Why are you surprised? English technical thought 
In fact there is a low pressure switch in the compressor.
“Early cars (up to about 1988) used the A6 compressor with a high temperature switch. This switch detects the temperature of the interior of the compressor and if it exceeds a certain point it goes short circuit which in turn blows a one-time thermal fuse which opens the circuit to the compressor clutch thus switching off the compressor. Later A6 installations used a pressure switch in the same location on the backplate of the compressor which open-circuited the clutch drive if the pressure of refrigerant gas fell below a certain point (about 100psi)”
everything sounds strange what you tell me … 100 PSI ?? !! a bit much ? do you have a documentation with the 1990 xj40 with Sanden SD-510 compressor? everything else is only guesswork
Not too much, one zero too many 10psi->0,68bar
Normal operating ambient temperature range is: - 24 to 43°C.
Normal operating evaporator temperature range is: - - 1 2 to 0°C.
Under normal running conditions system pressure should be as follows:-
Low side: - 103.42 to 206.84 kN/m2 → 1,03-2,06 bar
High side: - 1275.50 to 1434.1 0 kN/m2 → 12,75 bar to 14,34bar
compressor.pdf (311.2 KB)