Auto Air Conditioning & Heater Repair: 2000 F150 AC Recharge, ac recharge, other vehicles

Question
I tried to recharge my AC.  I thought I had the quick connect hooked to the low pressure, back near the fire wall on the passenger side of the truck.  It began to blow back at me when I connected the hose assembly to A/C system. No 134a got into the system.  Was I on the wrong connector?  I thought the hose assembly I had would only connect to the low pressure side.  I have done a couple of other vehicles with it a couple of years ago.  Does the truck need to be running for the recharge?
Thanks for the help.

Answer
Adam,
You are absolutely right. R134a fittings are designed so that they are different sizes. The simple gauges and connectors that you buy from autozone or wherever will only connect to the low side port in the system.
When you say it was blowing back at you, what do you mean? Where was it blowing from? Did it continue to blow out when you removed the fitting? If it was blowing at you with the gauge attached, that leads me to believe that the fitting you have with your kit is faulty. Or perhaps you weren't able to secure it to the fitting completely, but it was on enough to depress the schraeder valve inside the port. All I can say is to try it again and see what happens. Make certain it is locked on the port completely before you depress the fill button.
And yes, the truck's engine and a/c should be on while you are charging it. It is charging by the process of trying to equalize pressures betweenthe can and your system. If you leave the truck off, the pressure inside the can will be the same as or close to the pressure inside the system and nothing will flow. With your compressor on, it is pushing refrigerant through your system, as the refrigerant hits the metering device a low pressure is created. Therefore, preuusre will flow naturally from the higher pressure in the can to the lower pressure inside the low side line. It will also speed the process if you heat the can up in hot water. The heat absorbed into the can raises the pressure even more inside the can so it will flow faster. This works for shaving cream cans and spray paint cans also to get the last bit out of them. But do not use an open source of heat such as a flame, this can cause the pressure to raise too high and explode the container.
I hope I was able to help a bit, If I can do anything more, do not hesitate to ask. Good luck in everything and thank you for the question