VMAC - Vehicle Mounted Air Compressors
VMAC Technical Support: 888-241-2289
VMAC Knowledge Base: kb.vmacair.com
78
Throttle Control Testing
Read the “Maintenance and Repair Safety” section prior to
performing any work on the system (beginning on page 47).
Wear appropriate Personal Protective Equipment and follow all
industry standard safety practices.
The air pressure (inlet valve) and engine rpm (throttle actuator) are controlled by
the unloader valve. As air pressure from the unloader valve increases, it forces the
throttle actuator to reduce engine rpm. Once the system has built to full system
pressure (140 psi) the force from the unloader valve will move the throttle to base
idle.
While the system is building air pressure, the PTFE test tool gauge will indicate 0
psi and the throttle will be wide open. Once downstream pressure reaches 140 psi
it will actuate the unloader valve, which opens the discharge valve. The PTFE test
tool gauge will indicate 140 psi and air pressure from the discharge valve will force
the throttle closed. When downstream pressure drops below 120 psi the discharge
valve will close (the PTFE test tool gauge will indicate 0 psi) and allow the throttle
to return to its neutral state of wide open.
The following testing is for systems set at factory pressure (140 psi).
With the system off and depressurized:
☐
Install the VMAC Air Test Tool (P/N: A700052) on the system outlet (Figure 52).
☐
Install the PTFE test tool (Figure 40 and Table 6 on page 69) on the 1/4 in
throttle tube (Figure 52).
Figure 52 — Test equipment installed
(Scavenge tube not shown)
Unloader
valve
VMAC Air Test
Tool (A700052)
Throttle
actuator
3/16 in pressure
control tube
1/4 in pressure
control tube
Discharge
valve
PTFE Test
Tool
