Im a part time assistant manager and a full time certified Ford tech. If the system blows hot air, it means either it has a leak which is very common, or a previous owner for some reason discharged the system and never recharged it. Not likely, but possible. In any case, you need to find the source of the leak which any garage can do. Most common way is a UV light to search for traces of dye. Every Ford car since 95 has a dye pellet in the AC system. If its been open to atmosphere for too long, the dye may be hard to find so like has been stated, it may need to be charged and injected with dye to find the source of the leak. On our cars, common leak points are the service fittings (most people replace them with a newer style), and Ive seen several cars with holes in the condenser. Back to my main point, having the background at the dealership has taught me to try and steer people away from using parts stores R134a, especially the ones that contain stop leak additives. The stop leak in these products is activated upon contact with moisture and then turns into a goop similar to RTV. The theory is that the AC system is free of moisture so if theres a leak in the system, the sealer will seal a bond at the source, IE the leak. The problem with this is a system that has a small leak will have a LOT of moisture in it since its been open to atmosphere for some time. So now youll have sealant spreading throughout the system, which usually clogs the service ports and more importantly, the fixed orifice tube. This is the small element inside the system that has tiny filter screens and is the seperation between the high and low sides of the system. If this gets clogged, which is fairly easy, youll be back to no AC only now youll have to pay a shop to flush your system, replace the orifice and possibly the service fittings, on top of whatever the original leak was. I steer people away from a lot of the R134a products at Advance. If the system worked for some time and then started blowing warm air theres a concern that needs to be addressed. Not all 134A products will have stop leak so if your convinced you just need to throw some freon in it without fixing the concern, be sure to get one without stop leak additives. And for people with new cars under warranty that may have decided to throw this junk in the system instead of bringing it into the dealer, most places now require the freon to be tested for unauthorized stop leak and signs of hydrocarbons (some places have filled systems with propane instead of refrigerant since its cheaper.. and yes, it will cool your car just as good as 134A.. until you get into an accident and some 500 PSI propane ignites)
