What the pressure reading should be when recharging AC on a 1999 GMC Suburban?

There isn't a single pressure reading for recharging the AC on a 1999 GMC Suburban. The correct pressure depends on several factors, most importantly the ambient temperature. You need to consult your Suburban's owner's manual or a reliable AC repair manual specific to that year and model. These manuals will provide pressure charts showing the low-side and high-side pressure ranges for different ambient temperatures.

Attempting to recharge your AC system without this information is risky. Overcharging can severely damage the compressor, and undercharging will result in poor cooling.

Instead of trying to find the pressure yourself, consider these options:

* Consult your owner's manual: This is the best place to start. Look for a section on the air conditioning system.

* Find a repair manual specific to your vehicle: Repair manuals often include detailed AC system diagrams and charts.

* Take it to a professional: An automotive technician with AC service equipment will have the proper gauges and knowledge to accurately diagnose and recharge your system. This is the safest and most reliable method. They can also identify other potential issues (leaks, etc.) that a simple recharge might not address.

Do not rely on generic pressure readings found online. These can be inaccurate and lead to damage to your AC system.