engine pinging when a/c is on

[Touchdown038]

So I just finished flushing and recharging the A/C on my S13(R134a conversion) and it runs fine until the engine gets warm, where anything above half throttle going uphill will make the engine ping like crazy. It doesn't do it with the A/C off, though. Timing is set at 15º so I'm thinking the intake temperature has something to do with it? Possibly my cone filter sucking in warm air because it's right next to the exhaust manifold?

I really would like to get this fixed soon, because I need to go back to school and would like to have the A/C working in 90's weather. Any ideas?