Chevrolet 1999 Express Van Owner's Manual page 306

Air Conditioning Refrigerants
Not all air conditioning refrigerants are the same.
If the air conditioning system in your vehicle needs
refrigerant, be sure the proper refrigerant is used.
If you're not sure, ask your dealer.
6-70
Air Conditioning Refrigerant Capacity
NOTICE:
-
R 134a refrigerant is not compatible with R
refrigerant in an air conditioning system. R
-
an R 134a system will cause compressor failure,
refrigerant oil sludge, or poor air conditioning
system performance.
TYPE QTY Front Only
Refrigerant 3.00 lbs. (1.36 kg)
-
R 134a
yellowblue
-
12
-
12 in
QTY Front
and Rear
4.5 lbs. (2.04 kg)