My 1991 Reatta has had it's air conditioning system serviced after the compressor clutch failed. The compressor, condenser, dryer, and orifice tube were replaced and the system was recharged with R-12. Since then, the air conditioner works very intermittently and usually at very light throttle or upon deceleration. The system pressures are correct and no warning lights are displayed. Is there a system pressure switch that could cause this problem or is there something else that should be checked? Thanks in advance for any ideas to help solve this problem.