When you change the ac compressor on a 03 trailblazer how much Freon goes back in it?

With system under vacuum, refrigerant will go in without the compressor running. As pressure comes up in the system, the compressor will begin to run, creating a lower pressure on the Low side. System needs to be under a vacuum to start. Make sure you only fill to the specified amount.

Two things are very likely to be your problem. Freon or compressor. Turn on the ac on cold and see if the compressor is engaging, if it is and stops and goes or if it doesn't. try to check the compression on the low side of your ac, the smallest plug where you service the ac. Or take it to an ac professional to get it refilled or checked. Remember, just because its blowing air, it doesn't mean its working. There are fans inside the car that push the cold air inside your vehicle and most of the time these will work, but that's not the only part required to blow cold air inside your car, the compressor is what makes the air cold.

A few things could be wrong here. 1. if your running low on anti-freeze and your engine is getting hot, the thermal switch on the AC compressor will shut it off until it cools down. 2. You could be low on freon. 3. Your compressor may be bad with leaks.

probably low on freon

compressor locked up? maybe to much freon or a plugged oriface filter

It's your automatic A/C Clutch bearing. The computer tells the clutch to engage and it connects to the compressor but the bearing is shot and attempts to seize thus slowing the motor. I would not run the A/C until the unit is repaired.

Check these items to narrow down the issue. HVAC in cars works on two different systems.

Air conditioning checks you can look at are

1) With engine running, turn on your AC on high as cold as it goes. Under the hood, listen for a clicking sound from the compressor. It should click on and off as the belt goes around the compressor every 15-30 seconds, or sometimes shorter or longer. IF this is working, then, the compressor is likely okay. However if not, then the compressor will need to be replaced.

2) IF the compressor is working, then it is either a low freon in the system issue or a leak in the lines in the system. This typically can be checked quite easily depending on the AC symptoms prior to the AC not working. If the AC worked, but slowly has not been working, or it works for a few seconds early in morning, and then stops...it's a low freon issue. The only way to check to see if it is leaking is to do some diagnostics by going to your local auto parts store and retrieving the proper freon for the vehicle as well as a freon filling tool. Shouldn't be too expensive. Follow the instructions on the can, and put one to two cans of freon in the system. The AC should work nearly instantly. If it goes back to hot within a day or two, then the lines/seals are probably worn or broken and it is leaking. The best option you can take after this, is to a certified AC repair shop as it will much easier and less frustrating for the home mechanic.

Hope this helps!

Chip

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.

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.

check to make sure the compressor is engaging, check the ac relay