The following procedure can be used to
evaluate the adequacy of the charge level in a vehicle air conditioning
system:
1. Operate vehicle at Fast Idle with the A/C on High for 10 minutes;
2. Measure the ambient air temperature: Tamb = _________ºF;
3. Add 33 Fº to Tamb: 33 + Tamb = _________ ºF = Condenser
Temperature Index
4. Using the (HFC-134a) refrigerant tables, find the closest pressure
corresponding to the Condenser Temperature Index from step 3: Condenser
Pressure Index = _______ psig
5. Measure the condenser pressure, psig: Pcon = ________ psig
6. If the Condenser Pressure Index found in Step 4 is within plus or
minus 10 psig of the condenser pressure found in step 5 (Pcon), the
refrigerant charge level is adequate and no charge need be added or
deleted;
7. If the Condenser Pressure Index is more than 10 psig lower than
Pcon, the refrigerant charge is too low. Increase the charge by four
ounces and repeat Steps 1 through 6 until the Condenser Pressure Index
is within plus or minus 10 psig of Pcon;
8. If the Condenser Pressure Index is more than 10 psig higher than
Pcon, the refrigerant charge is too high. Decrease the charge by four
ounces and repeat Steps 1 through 6 until the Condenser Pressure Index
is within plus or minus 10 psig of Pcon.
