A/C system charge??

Anyone know the right way to charge a 99 Yukon dual control A/C system??

I'm confused on how to have the switches positioned...

I tried with both switches in the High position but it over charged the rear and didn't put enough charge into the front.

Thanks for your help....

btw.. have searched

There's only one system, with one compressor and one fill / test valve. Something else may be wrong, such as the doors in the front ducting may be malfunctioning and letting hot air mix with the cold.

Not sure if this may help, but on the dual A/C systems, they need more pressure in the system than the single systems. For instance, 1.8 lbs front only compared to 3.6 lbs. with front/rear a/c. These numbers are for the 2nd gen trucks though w/134. Not sure of the 1st gens.
Just a thought. Good luck.

Thanks for the reply....

Anyone else??