By 'front a/c system' I guess you're referring to the dashboard air, not the front rooftop unit? The dash air could be not working for a number of reasons.
Often the heater control valve isn't shutting off completely and hot water is still flowing into the heater core, negating the cooling power of the A/C. Remedy, check what type of control valve you have, mechanical, vacuum, or electrical and adjust or install a ball valve to stop coolant flow.
The R-134a coolant used in most modern automotive A/C systems isn't technically Freon, which is a registered product by Dupont R-12 coolant. The system usually has a sticker identifying the type of coolant and the amount needed for a full system. The sticker on a DP could be up front, 'under the hood,' on or near the HVAC plenum. In addition, it could be near the engine and A/C compressor. On a gas unit, it could be on the radiator support or near the HVAC plenum. Problem is, if you just add coolant without finding the leak or how much oil is in the system, it will just continue to leak down.
Also, just adding coolant with the kind of can and hose, perhaps with a low pressure gauge found in Walmart and auto parts stores, doesn't give the true charge level of the system. It's better to use an A/C manifold system that monitors high and low pressures. The pressures are dependent on temperature and shouldn't be ignored. The manifold costs about $60-$120. If you go to an auto A/C shop, not only do they have the manifold but also a 'sniffer' that can find the leak and won't cost as much as the gauge set needed to do it properly.
I think it's worth the money to have it done right, and this is a person that tries to DIY on most every project.
By the way, the amount of R-134a needed to fill an RV unit is little more than usually found in an automotive unit. Despite the size of the vehicle, it's not a huge difference, perhaps a few ounces more than a car or pick-up. If you identify the manufacturer of the HVAC system, it might be found at their website.
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