on these dual systems do you charge them with liquid, (can upside down) or with gas (right side up) i have all the equipment to evac and pull a vac on the the system, but i know some vehicles require you to charge them with liquid , but i know it is not wise to charge with liquid with the low pressure schrader valve on top of the compressor, i sure could use some help please. thanks

 

Donald, you never ever charge the A/C system with liquid going in. You can lock up the compressor and/or blow a valve due to hydraulics. When you see an A/C guy turn the can upside down, it is just momentarily as the pressure on the can starts to drop and it gets harder to push the gas into the system.

I never push liquid going in unless the low pressure valve is installed on the low side accumulator. The accumulator stores excess liquid coming from the low side to prevent liquid going to the compressor.

If you use those little 1 lb cans, you can prepare a pot of boiling water. As soon as the can looses its pressure and equalizes with the pressure in the system, just put the can in the hot water and it will immediately boil away the remaining freon in the can and push it into your system.

Now if you are using those big 30 lb drums, they have enough volume to maintain gas pressure to fillup your A/C system.