THE FREON PRESSURE IS 40 WHEN THE COMPRESSOR IS NOT RUNNING, BUT WHEN I JUMP THE COMPRESSOR TO MAKE IT RUN THE PRESSURE DROPS TO ABOUT 10

You can add freon without the compressor running. There is a pressure switch in the system that prevents the compressor from operating when the freon pressure is too low. Just add some freon and once the pressure increases, the AC clutch will engage.

Put more freon, so that the high-pressure sensor going to close and your compressor will run.

Sounds like the fittings are reversed.
With the compressor running, the low side should drop below zero then climb to 60 or 80 psi as you add freon.
You would need to jumper the low pressure switch to engage the compressor clutch to add freon. The compressor must be running.

Grab some refrigerant gauges and take readings. If the low side has more than 40 psi or so of pressure, the low limit switch will close and allow the compressor to run. If there is indeed low pressure causing the compressor not to run, you will need to flush the system after eliminating the source of the leak. If the a/c compressor has never been changed, it is probably the source of the leak.

The condenser is not where refrigerant is added to

You need special training & equipment to work on A/C
System

Have a repair shop diagnose the problem

Normal pressure with the engine-compressor off is outside air temp. So both gauges would read 70 or 80 or whatever.
When the system is running, normal is 30-50 low and 200-300 high.
One thing that comes to mind to test is the low pressure switch.

The pulley on the compressor is always running when your engine is running, but the only time
it compresses the freon is when the clutch engages, if the compressor's pulley was not turning,
it would have already snapped a fan belt or your serpentine belt. voltage runs from your fuse box
thru your air condition switch on your dashboard to a low pressure switch that is located at the
accumulator a long cylinder,close to the firewall under the hood or close to the condensor, front
of the car. the switch detects freon pressure in the accumulator, if there is freon pressure, the switch
will stay closed and allow voltage to go to the compressor clutch to engage it and compress the freon,
if there is no freon pressure the switch will open, and there will be no voltage to air compressor, its a
saftey switch to keep your compressor from getting damaged.its possible that the switch could be bad
it may not have voltage at the switch, or it may be open because there is insufficient freon pressure.
check and make sure there is freon in the system.check for voltage at the low pressure switch if you have freon in your system and voltage at the pressure switch, set your ac on high, pull the molex off
the switch, and jump it out with a jumper wire, if the clutch engages and your car starts to cool, just
replace the switch. if the clutch engages but does not cool, then your ac system has some blockage
in the lines. if the clutch does not engage at all then it would be the compressor clutch. good luck!

Hello, You need to check how much Low end pressure you have. The Low pressure cutoff switch will disconnect the compressor if the pressure is too low. The high end pressure switch will do the same thing for extreme pressure.

Sometimes the Low pressure switch will get weak and cut off the system too early. Just change this switch which will come out with only a slight puff of Freon being lost. You can jump the connector with a U shaped wire and bypass the Low pressure cutoff switch. If the compressor works better and does not cut out, it can still be low on Freon or have a bad Low pressure switch.

However, if the compressor cuts out a Second time with the Low pressure switch bypassed, the system is probably overcharged and the HIGH pressure switch is cutting off the compressor. You need to purge some Freon out of the system if High pressure is indicated.

Where it gets tricky is the Compressor will compress both Freon and Atmospheric air. Your efficency drops when the Freon is displaced by Atmospheric air. You will need to find the leak in the system which is allowing Freon to leak and outside air to enter the system. You will get a pressure reading with any gas in the lines.

There are Leak detectors and sealers for the system. I hope you just have a bad low pressure switch which is the easiest solution.

Jumping the switch is only recommended for very short periods of time to check the compressor itself. The problem with straight-wiring it is that the compressor will run all of the time. During normal operation, the compressor cycles on and off depending on the pressure inside the A/C system. If you run the compressor all of the time, you run a risk of causing substantial damage to your A/C system, your car, or even yourself. The compressor would be constantly pressurizing the system until something releases that pressure. It may be an A/C hose or it may cause something larger to explode under the tremendous pressure. Be very careful with the A/C system and get the advice of a licensed A/C technician.

The interuptions in compressor engagement is due to low side drops which is controlled by the pressure switch mounted on the low hose or large metal accumulator on the passenger side. Low side hoses are larger and the accumulator is on the passenger side engine compartment...a paper clip works fine jumping this low side pressure switch out until freon pressures increase enough to keep compressor running to accept freon.