Hello: I have a dual R12/R134a a/c recovery/recharge unit. I'm trying to charge my 1990 300SE with virgin 134 after recovering what was in the system and then pulling a vacuum on it.

I cannot get the charge into the vehicle as the pressures are too high. I've found that the pressures are high in the hoses while they aren't even hooked up to the car's a/c system. I have had the a/c unit remove the pressure from the hoses and then I hooked them up to the vehicle. However, only approximately 7 ounces of refrigerant gets sucked into the system before the pressure builds again and inhibits more refrigerant from being drawn into the vehicle's a/c system.

Either I'm doing something wrong or there's something wrong with my recovery/recharge unit.

If someone with experience using auto a/c recovery/recharge units can walk me through this I would appreciate it. I would not mind paying for a phone consultation. I can send payment via PayPal.

Please send me a PM or post hereon if you are able to help.

Thank you.