Code 61, A/C System Performance: Notes

A/C refrigerant charge is calculated by inputs from the A/C refrigerant pressure and A/C evaporator temperature sensors. PCM will calculate system charge when the A/C is turned on. A/C evaporator temperature, A/C refrigerant temperature and vehicle speed are factored together to yield a minimum charge allowable for the A/C system to operate.

If system charge falls below a given value for the temperature and vehicle speed variables, Code 61 will set. As ambient temperature falls, so does static (A/C off) refrigerant pressure. This produces a sliding scale which requires temperature, pressure and vehicle speed inputs to calculate a reliable system charge value that indicates when A/C refrigerant charge is too low to safely allow compressor to operate.

1. This test determines if code is intermittent and will also check A/C system for other failures. Repair all other codes before proceeding. Use appropriate A/C service manual to verify proper gauge readings. Pressures vary with temperature and humidity.
2. This test is to evaluate the A/C refrigerant pressure sensor for accuracy. A reliable gauge set should be used and no more than 20 psi difference in pressure between gauges and scan tester is allowable.