Usually you will not get an accurate oil pressure reading either too high or too low. Occasionally they will leak and pump oil through the switch
all you have to do is fallow the line coming out of the compresser on is the high side the smaller fitting is the low side
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A pressure switch a valve that shuts off the unit when the pressure is to low or to high
it does not have a high pressure switch all it has is a evaporator temp sensor/switch.
You will definitely lose all of your Freon when you replace the high pressure switch. Once the high pressure switch is loosen the Freon will begin to access the system.
There is a resistor/ circuit board near the heater motor that need to be replaced. You can get one from almost any auto parts store.
The headlight switch may be bad. Try replacing. Its the Headlight switch. The switch has a built in Circuit Breaker that self resets. It has become bad and will eventually give it up.
The low pressure port on any A/C system will be the the line running from the compressor and going into the evaporator in the passengercompartment. The high-pressure port is in the line coming from the condenser in front of the radiator going to the compressor.
a hi pressure switch will limit the pressure by stoping motion (turn off motor) (unload cyclinder) ect
A pressure differential switch, is a switch that reacts to pressure difference of two points, usually your supply & return side. If the pressure between these points are high, it then "reacts" notifying of pressure problem on the system.
On a '99 suburban, the low pressure a/c port is on top, towards the back of the compressor, and pointed forward. The high pressure port is there also, just behind it and to the left, pointed straight up.