You will weight the can of refrigerant and as you charge the system you will continue to weight the can of refrigerant until 1 lb. has been removed. Most shops don't use the small cans of refrigerant but buy them in bulk size so they just put the container on a digital scale and watch the scale until 1 lb of gas is removed from the container.

Before adding refrigerant to the system you should determine if the system is low to begin with. What are the high side and low side readings? What is the static pressure if the compressor is not engaging. Does the compressor engage?

I had a bad condenser fan which the DME was able to log a fault code and if the aux fan is bad, I don't think the DME will enable the compressor to engage. Replaced the aux fan and my ac is working fine, whereas before the compressor wouldn't engage.

Before blaming low refrigerant, get the truck scan to determine it's not something else that causing the ac not to cool. Pressing the shraeder valve on the low side is not a valid test for determing the amount of refrigerant in the system.

__________________
2006 Infiniti G35
2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD
Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD