2007 F250, 6.0 I just replaced the evaporator and accumlator. I vacuumed the system and refilled the system with refrigerant. The ac works great, I'm getting a duct temp of 35 degrees. I Decided to check the pressures with my manifold gauge set. Ambient temp is 70 degrees. After hooking them up I turn on the low side and get 38 on the low side and 150 on the high side. I'm getting this reading with only the low side open, the high is closed. When I open the high side the low side will spike to 120psi! When I turn the high side off it goes back down to 38 and 150. Should I be getting a reading on the high side gauge even when the gauge is closed? Are my gauges defective or do I have another problem? I don't think I overcharged it, the sticker under the hood calls for 2.82lbs, I used the 12oz cans so I put in 3 cans and using a refrigerant scale 9oz out of the last can for a total of 45oz. Any help would be appreciated!