Before or after overhaul, Dodge trucks equipped with the AS68RC may exhibit a complaint of diagnostic trouble codes related to pressure switches number 7, 1 and 2, which were replaced with new switches during overhaul (figure 1). From all the calls taken with this concern, the problem have occurred with 1/4 NPT switches only.
The cause seems to be that these new 1/4 NPT pressure switches are not functioning correctly out of the box (figure 3). We have had reports of new 1/4 NPT switches not functioning consistently until the switch is supplied with 150 pounds of compressed air. Afterwards, the switch performs correctly, consistently closing at its rated 65-70 psi.
It is suggested that when replacing these switches, apply compressed air prior to instillation to verify that the switch closes consistently at 65-70 psi with 1/4 NPT switches and 45-50 psi with 1/8 NPT (figure 4). If new pressure switches are needed, it is best to buy them through Isuzu. Many thanks to Nick Gulmezian in New York.
The part number for a new 1/8” NPT pressure switch (#3, 4, 5, 6 & 8) is 8-98179-072-0.
The part number for a new 1/4” NPT pressure switch (#1, 2 and 7) is 8-98179-073-0.
