I have a 2007 dodge ram. If I turn the a/c on it blows hot. I figured the hot means low freon so I put a charge in it. Afterwards it blew cold but only at 1/2 volume and sounds like it should be blowing more air. I figure there's a vent stuck closed somewhere. I let the freon charge run its course and need a new charge again but would like it to blow harder like an a/c system should. Help

check for clutch slippage --and when charging system was it done at idle [which is incorrect ] or at raised rpms may be low on freon

A mechanic would check the system with a set of pressure gauges. If the compressor is running, the low side would read around 30psi and the high side would be around 250psi. That is how you know if the system is full of freon or not.
You may have to get a professional diagnosis to proceed. If you replace the compressor, the accumulator needs to be replaced and a vac pump is used to pull all of the air out before the freon is added.

bypass the pressure switch with a wire and see if the compressor kicks in. What are your pressures? Ambient temp? An over-charge should not lock up the compressor. It is a closed system so you definetly have a leak somewhere. use soapy water around joints looking for bubbles.

The problem could be it is low on freon. Have it checked out, you will probably need a freon boost.

you say it will blow cold and hot air for only a few minutes. You don't say but I assume you mean will blow cold a few min. when turned on AC max , blow hot only a few min. when turned to heater hot. Assuming thats the situation and you say AC charged and shows good on the low side -you should charge the AC to a full charge on the low side will cause problems with the AC air compressor kicking on and off. I suggest while the engine is running and turned to AC cold max watch the AC air compressor clutch to see if it does indeed kick on and off if so charge completely. As far as the heater make certain you coolant is all the way to the top and the best way to do this is when engine is completely cold remove radiator cap and fill completely and completely close cap then fill overflow container just to the cold level. That should fix your problem.

It sounds like a low charge. It could be a clogged expansion device also. It has a higher probability of being a low or contaminated charge.

Have you checked for freon leaks. It sounds like it's low and the pressure switch drops out. Try adding freon.

expansion valve looks like is not openning or the capilary tube is bad

More likely the recharge blew a o-ring and you have a leak. When your Cavalier was blowing hot air and a recharge fixed it that means it was low on freon which lets o-rings dry out, go back to the shop and have them leak test it. They use a pressurized dye to find the problem. If it's blowing it's not the cooling fan relay, they may have meant compressor relay but I'd have a leak test done first it's not expensive and easier that chasing unknown possibilities.

check for the freon charge level.if the freon is too much definitly your compressor will turn and off every 10 seconds