Top 5 VMAC Hydraulic Air Compressor Control Box Features

November 18, 2018
hydraulic control box

Hydraulic Control Box

The control box in the VMAC hydraulic air compressor is the computer that tells the compressor what to do and when to do it. Control boxes also give a voice to air compressors and allow them to share important information via the display box that can help with system maintenance, operation, and diagnosing issues.

If your VMAC hydraulic air compressor doesn’t have a display box, it is an earlier model that utilized red and green indicator lights instead. These lights will display in patterns, similar to Morse code, to communicate. To learn more about these indicator lights and what their patterns mean, please visit the Hydraulic Air Compressor Error Codes guide in our Knowledge Base.

Top 5 Control Box Features

The VMAC hydraulic air compressor control box has numerous features, including:

5. Air Filter Reminders

The display box will remind you to check the air filter every 100 hours and it’s at your discretion whether the filter should then be replaced. The air filter reminder will go away on its own after 6 hours of operation.

4. Service Reminders

Every 500 hours, the display box will let you know that it’s time for servicing. Use the instructions in your VMAC service kit to complete this work, and then log the service work as complete. The hydraulic air compressor control box will maintain a record of the last ten system service times, for your record.

3. Temperature Warnings

The hydraulic air compressor also has a fail-safe mechanism that prevents the system from getting too hot by automatically shutting down. The display box will let you know whether it’s the air compressor or the hydraulic oil that is overheating, which will help diagnose and resolve the issue.

In addition, the display box will notify operators during start up if the hydraulic oil is too cold (below -13°F or -25°C) or in the process of warming up.

2. Errors & Service Diagnostics

The VMAC hydraulic air compressor will also display error messages on the display box. These error messages can help operators and service techs diagnose the issue and, as a result, implement the most efficient fix possible.

1. Modify System Parameters

One of the coolest features of the hydraulic air compressor control box is the ability to modify the system parameters from the default settings to the settings that make the most sense in your environment. You can modify the following parameters:

  • System Pressure
  • Temperature Sensor Overrides
  • System Restart Pressure
  • Standby Delay

You can also review the PSI and temperatures by pressing the ON button repeatedly until the data is displayed on the display box.

Change Your Hydraulic Air Compressor Defaults

Setting Description Default Adjustment Options
Standby Delay Delay time to standby 2 minutes 30 sec, 45 sec, 1, 2, 5, 10, 15, 30 minutes, Never
System Pressure Maximum operating system pressure 150 PSI 110 to 150 PSI
Restart Pressure PSI Air pressure set-point for pressure-based restart 120 PSI 80 to 120 PSI (limited to 30psi or more below the UNLOAD PRESSURE)
Temperature Probe Override (Temporary) Override temperature controls to perform emergency system maintenance Disabled Enabled

Hydraulic Air Compressor Display Box Messages

The following messages have been coded into the hydraulic control box and will be displayed on the display box:

Power ON, System Off

Message/Problem Possible Causes Corrective Action
No power to display box Fuse blown or bad connection Check components, replace fuse inside system

ON button pressed/initial start up

Message/Problem Possible Causes Corrective Action
SOFT START XXXPSI The system has started, but the compressor oil temperature is still cool. The system is in “Unload” Mode, until the compressor has come up to temperature
+122°F (50°C).
HYD OIL TOO COLD The hydraulic oil is below -13°F
The system is cautioning the operator to preheat the hydraulic oil before starting the PTO system. The Cold Climate Kit (A700146) can be installed to speed up the warming process once the hydraulic oil temperature has reached –13°F (-25°C).
The hydraulic oil is between -13°F(-25°C) and +5°F(-15°C).
Keep circulating hydraulic fluid until the system warms sufficiently to start. If installed, the Cold Climate Kit (A700146) will speed warm-up. The System won’t start until the hydraulic oil has warmed to +5°F (- 15°C).
System does not start when the ON button is pressed. 1. Inappropriate conditions for start-up.
2. Hydraulic solenoid failure.
3. Hydraulic motor or compressor seized.
1. Check display box for messages.
2. Check solenoid and connections.
3. Check motor and compressor will roll-over.


Message/Problem Possible Causes Corrective Action
STANDBY XXXPSI The air pressure stayed above the restart pressure for the duration of the standby delay time. The hydraulic solenoid is off, and the system is monitoring air pressure and compressor and hydraulic oil temperatures. If the air pressure drops below the restart pressure, or the
compressor oil temperature drops below its minimum, it will restart and rebuild air.

Air pressure won’t build past approx. 40psi.
1. The system is in SOFT START.
2. Unload solenoid on inlet valve has failed or problem with wiring connections.
3. Pressure sensor has failed or
problem with wiring
1. Wait for the compressor to warm up.
2. Check solenoid and wiring.
3. Check pressure sensor and wiring.
Low system air
1. Air reservoir drain open.
2. Air leak.
3. System demands
exceed compressor delivery.
4. Blowdown system stuck.
1. Close valve.
2. Check all fittings. Check air lines for wear/damage.
3. Reduce air demand. Check for correct amount of hydraulic flow for the desired CFM.
4. Check for air venting from blowdown cap while running.
Compressor stalling/not building air. 1. Hydraulic relief valve lifting.
2. Hydraulic flow too low.
3. Unload Solenoid Failure
1. Check hydraulic pressure while running. Check for other relief valves in system set too low.
2. Check for correct amount of hydraulic flow for the desired CFM. Ensure that engine rpm is being maintained when load is applied.
3. Check solenoid and wiring.


Message/Problem Possible Causes Corrective Action
Hydraulic oil is getting too hot and the compressor is shutting down.
1. Insufficient air-flow or ventilation.
2. Fan not operating.
3. Failed temperature probe or bad wiring connections.
1. Make sure the cooler is not blocked. Open door if installed in a cabinet. Improve ventilation.
2. Check connections. Check fan and relay.
3. Check the temperature probe and wiring connections in the hydraulic manifold.
HYD PROBE OPEN HYD PROBE SHORT Failed hydraulic temperature probe or bad
wiring connection.
Check the temperature probe and wiring connections in the hydraulic manifold.
temperature probe or bad wiring connection.
Check the temperature probe and wiring connections.
PRESSURE SENSOR? Failed pressure sensor or bad wiring connection. Check the pressure sensor and wiring connections.
CONNECTION ERR Failed control box, display box, or bad wiring connection. Failed control box, display box, or bad wiring connection.
System runs then shuts down, and display resets, but doesn’t restart
1. Wires connecting to battery positive and ground too
2. Low battery voltage.
1. Check wire size requirements in the installation manual and install the correct
gauge wires.
2. Check wiring connections. Measure voltage at the input to the air compressor when it is running with the fan on to
ensure full voltage. Check charging system.
High oil consumption 1. Compressor, hose, fitting, or cooler oil leak.
2. Compressor shaft seal leaking.
1. Check system for leaks.
2. Pull off hydraulic motor and check for oil inside coupling.
Excessive oil in air line 1. Excessive oil level.
2. Coalescer filter plugged.
3. Scavenge line plugged.
1. Check oil level and adjust as needed.
2. Check and replace as needed.
3. Check scavenge line and fittings.
Water in air system 1. FRL
(Filter/Regulator/Lubricator) failure.
2. Air reservoir not drained regularly.
3. Excessive water in compressor oil.
1. Check drain on filter.
2. Drain reservoir.
3. Allow system to completely cool, and drain water from tank until oil comes out. Top up oil as per manual.
Air pressure relief valve opens. Compressor system pressure exceeding
Check pressure sensor.

For further assistance with VMAC’s hydraulic air compressor, please call our technical support team at
1-888-241-2289 or visit the VMAC Knowledge Base.

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