My 2002 TB a/c works for 20 min. Then does not. Checked , no leaks, clutch turns, condenser clicks until blowing hot air, replaced low pressure switch

heres a few --blown fuse -relay -climate control switch / circuit -compressor failure --no or low freon -

There is a high and low safety switch on the system. When the pressure goes either way too much it stops the compressor.

If it works sometimes but not others, the most common faults are overheating components (AC clutch, control relays, ) pressure problems (high or low pressure or sensors reading too high or low after they are on for awhile), or defective blend door or temp control system.

AC isnt complicated. It really hasnt changed much at all in 20 years, and didnt change for 50 years before that aside from what refrigerant is put in. the theory hasnt changed. If you mechanic was checking condensers for leaks, and didnt find them, Id suggest someone more skilled at AC work. Condensers are NEVER EVER intermittent problems. They leak, or they plug solid. Neither condition comes and goes. Your problem is in system pressures, or electrical control, or clutch. Period.

Check that the heater is turning off as the hot air will over come the cool air. Check that the clutch on the a/c pulley is still engaging as it the unit was over filled or has a leak from a badly fitted pipe the high low switch will not allow the compressor to work.. If the work was done professionally check that the correct gas was used and seek warranty for the problem.

see this causes and fix it. God bless you
Compressor Checks
Start with the compressor. Does it engage when you turn on the A/C?
If so, the compressor is working and the A/C system probably contains enough refrigerant to make cold air, so the problem is inside the HVAC unit. Replace the motor that controls the blend air door (this is a difficult job and best left to a professional since it involves tearing apart the HVAC unit -- about an 8 to 10 hour job!).
If the compressor does not engage when you turn on the A/C, see if it will run by jumping the compressor clutch wire directly to the battery (use a fused jumper wire). If the compressor works when you jump it, and the A/C blows cold air, the system contains refrigerant and the fault is likely a bad A/C compressor clutch relay or a bad clutch cycling switch or pressure switch.
If the compressor does not engage when you jump it, the problem is a bad compressor clutch.
If the clutch engages but the compressor does not turn (the belt will start to slip and squeal), the compressor is locked up and you need a new compressor.
If the compressor clutch engages and turns the compressor, but the A/C still does not blow cold air, the system is probably low on refrigerant and needs to be recharged.
Refrigerant Checks
Connect an A/C pressure gauge to the HIGH SIDE service port (located in the high pressure hose that runs between the compressor and the condenser in the front of the engine compartment). The gauge will tell you if there is any pressure in the system. Simply depressing the service fitting valve with a small screwdriver to see if any refrigerant squirts out is NOT an accurate check because it tell you how much pressure is in the system. It may still have some pressure but not enough to trip the low pressure safety switch so the compressor will engage.
If your A/C system is low or out of refrigerant, check for leaks, then have the A/C system vacuum purged to remove air. After the air is out, it can be recharged with the specified amount of refrigerant. It is important to get any air out as this will reduce cooling efficiency and may make the compressor noisy.
A/C System Functional Checks
If the refrigeration circuit seems to be working (refrigerant in the system, compressor running and building pressure), but there is still no cooling, the problem might be an obstruction in the orifice tube (located in the high pressure hose between the condenser in the front of the radiator, and the evaporator located in the passenger compartment). A blockage here will prevent the refrigerant from entering the evaporator or recirculating through the refrigeration circuit.
If the orifice tube is plugged, the high side pressure reading will be lower than normal, and the low side reading will also be lower than normal because no refrigerant is circulating through the system.
If the refrigeration circuit seems to be functioning normally (compressor running, frost or condensation on the high pressure line from the condenser to the evaporator), but no cool air is blowing out of the ducts inside the car (and the blower is working), the fault is likely a BLEND AIR door that is stuck in the HEAT position, or possibly a badly clogged cabin air filter that is restricting airflow. Another possibility would be a fault in the automatic climate control system such as a ad interior temperature sensor or control module.

There is a possibility that there is not enough gas pressure in the system. The a/c compressor will protect itself by not allowing connection if the pressure is low. When the vehicle has run for a few minutes, and engine compartment gets hot, a/c gas pressure increases, allowing the compressor to turn on. With the engine turned off, test the a/c compressor clutch by applying 12 volts to the contacts. You should hear a click of the clutch engaging, and if not, the clutch is acting erratically.

You may want to have your fan clutch checked. If the fan on your water pump does not spin very hard when the vehicle is idleing than it doesn't draw air through the condenser and that air keeps the condenser cooler plus it keeps the pressure down on the high side of the ac system. leave comment.

Below is a guide to troubleshoot and check system function. This can be done by most folks.

Look at the front of the ac compressor and have someone turn on the ac from inside the car. The front of the pulley(clutch) will spin when turned on.

If it does not spin, the low pressure switch (LPS) is not satisfied. Meaning there is not enough freon in the system to operate the system. Means low freon capicity because of a leak.

The LPS can be jumpered to cause the compressor to run (clutch to engaged) which will draw the freon in the system.

The LPS is usually a two wire sensor on the suction of the compressor. (between evaporator and compressor) Unplug the sensor and install a jumper, this will engage the clutch. Connect a new can of freon
and fill to system capacity.

The capacity of the ac system will be on a label under the hood, do not overfill. Probably about 2 lbs. Local parts stores (Auto Zone and Advance) will have freon with stop leak. This may help the leak. They also make a freon with a UV dye. I always add a single can with dye so that if stop leak does not work I can find the leak in the future.

The system should be filled until suction pressure is about 30 to 38 psi..

Remember the flow for the a/c system is :
1. From the compressor a high pressure (HP) gas goes to the condenser in front of the radiator.
2. From the condenser a HP liquid goes to an expansion device (orifice tube or expansion valve)
3. From expansion device the low pressure gas enters the firewall to the evaporator.
4. From evaporator the low pressure liquid/gas mixture goes through the dryer back to the compressor suction.

sounds like a leak. Have your system checked for leaks and re-charged. If the system is full of refrigerant, then check the pressure switch on the compressor and the pressure switch on the accumulator (dryer). If the pressure in the system is low, these switches prevent the compressor from running to prevent damage.

Check if compressor clutch is engaged when A/C is selected,
- if not, check low pressure gas sense switch
- if it is open circuit the system needs to be checked for leaks and re-gassed.
(To check low gas switch, just ( briefly!) bypass it - if compress clutch engages you have low gas press.)