Air Conditioning blows warm air

[neutral]

Don't know what year MX-3 you have but figure it's a 92 or 93 if you're using R12 refrigerant. R12 systems operate under somewhat lower pressure than newer 134a. Don't know the engine rpm or A/C activation conditions you tested the high side for, but 46 psi still sounds too low - even for an R12 system. If so, Grants nailed it and your refrig. needs to be charged so the pressure switch can allow the compressor clutch to engage. Running A/C w/extremely low pressure can damage the expensive compressor. The pressure switch prevents such damage by refusing to engage the comp. clutch until refrig. pressure is restored to a safe operating level. If a refrig recharge doesn't last, ya gotta refrig leak somewhere.