05 Express a/c charge question

Hi All, I recently had the engine changed in my 05 Express. It is a passenger van and has the front and rear a/c units. During the engine change the a/c charge was lost. I am in the process of charging the system back up with R134a and wish to know when the charge is correct. I have looked up other Chevrolet models and they have suggested counting the cycle seconds of the compressor clutch. I have an infared thermometer that I have used to determine the coldest air coming out of the vents at different charges. Is there a different way other than these? Thanks.

Hi All, I recently had the engine changed in my 05 Express. It is a passenger van and has the front and rear a/c units. During the engine change the a/c charge was lost. I am in the process of charging the system back up with R134a and wish to know when the charge is correct. I have looked up other Chevrolet models and they have suggested counting the cycle seconds of the compressor clutch. I have an infared thermometer that I have used to determine the coldest air coming out of the vents at different charges. Is there a different way other than these? Thanks.

If the engine change place took it out they should have saved it and put it back in it.
Days of just throwing in R-134a is over.
To recharge you will need the proper tools.
And do not even think about one of the one hose one gauge any oil wlamart death kits.
http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=DIY
http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=RefrigerantGaugeSets

The correct R-134a charge sould be on ac sticker under hood or on reciever dryer.
Also the correct ac oil charge.