Underhood Troubleshooting

UNDERHOOD VR70 and VR150 Air Compressor Troubleshooting

If you are experiencing any of the problems listed below, simply click on the item to view possible causes and the corrective action you can take.

Frequent Clutch Burnout.

Possible Cause
Turning on the compressor with pressure still in the system.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
If the green light isn’t flickering, check the clutch connection.Also, try powering the clutch right from the battery with the engine running. See if it still cuts in and out.
Follow Test Procedure 1

The green light on the control box may flicker.

Possible Cause
Loose connection at:

  • Clutch,
  • Interface cable,
  • Key-switched 12V,
  • Park Brake,
  • DDC,
  • Ground, or
  • the green connector between the Switching Box and Low-Profile Control Panel.

Corrective Action
If it does, check the resistance between clutch wire (unplugged) and the battery’s negative terminal. The resistance should be between 2.3 – 2.5 ohms. Try wiggling the clutch wire while testing to check for an intermittent contact. If it does not, work from the Key-Switched 12V source, checking each connection.
Repair any loose connections found. Probing connection points with an analog voltage meter should show any intermittent connections. Alternatively, a test light may flicker with an intermittent contact.

The clutch engages and disengages while VR system is running.

Possible Cause
Failed component in Control Box, Low-Profile Control Panel, Switching Box, or DDC. The engine may run “rough” when the system is on, due to the throttle power turning on and off with the clutch.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
Note: An Analog meter has a needle that moves with voltage, and will flicker as the voltage changes, whereas A modern digital meter samples the voltage many times per second and averages these values. This can result in intermittent contact problems being missed.

Compressor does not run.

Possible Cause
Failed component in Control Box, Low-Profile Control Panel, Switching Box, or DDC.

Oil temperature too high.

Loss of 12 Volt signal at the clutch, blown fuse, broken wires or a failed switch.

Corrective Action
Isolate the Park Brake connection: Disconnect the black interface cable wire connected to the Park Brake. Connect it directly to ground. Run the system. Proceed to next step if problem persists.

Isolate the DDC: If it is an automatic, remove the DDC from the system, and ground the black Interface Cable wire. Run the system. Proceed to next step if problem persists.

Isolate the Throttle: For electronic throttles, if possible, disconnect the red throttle wire to bypass the throttle. Run the system. Proceed to the next step if problem persists.

If none of the above corrects the problem, the problem should be isolated to the control box in the system. Try replacing the Control Box, or the Switching Box and Low-Profile Control Panel as a pair. Turn compressor off, allow to cool for 30 minutes and restart.
Follow Test Procedure 1

No power to the clutch.

Possible Cause
Fuse burned or wires damaged.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
Check power at the clutch, replace fuse if necessary, replace broken wires or failed switch.

Engine stalls when the compressor is activated.

Possible Cause
System is under pressure.
Corrective Action
Allow 10 seconds for blow–down.

Possible Cause
Blow down valve not working.
Corrective Action
Replace blow-down valve.

Possible Cause
RPM setting too low or throttle not set correctly.
Corrective Action
Readjust RPM and throttle settings for optimum operation.

Objectionable noise level.

Possible Cause
Excessive gear wear.
Corrective Action
Contact the nearest dealer to replace compressor/gearbox assembly.

Possible Cause
Maximum RPM setting higher than necessary to meet air demand requirements.
Corrective Action
Reduce maximum RPM settings.

Possible Cause
Operating with the hood open
Corrective Action
Close the hood.

Bad clutch ground

Possible Cause
Open clutch stator windings.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
With 12 V applied to the clutch check for voltage between the clutch stator housing and the engine. If voltage is present, ground the stator.
With compressor switch off and clutch wire disconnected, check resistance between the input wire and ground.
Resistance (less lead resistance) should be 2.5 ohms to 3.0 ohms. If outside this range, replace the stator.

The engine may run “rough” when the system is on, due to the throttle power turning on and off with the clutch.

Possible Cause
Loose connection at:
Clutch, Interface cable, Key-switched 12V, Park Brake, DDC, Ground, or the green connector between the Switching Box and Low-Profile Control Panel.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
With power off, disconnect the Interface Connector (white connector). Check to make sure all the pins and sockets are in the same position in the connectors, and that there is no dirt or signs of arcing on them.
Repair / replace as needed. For systems with theLow-Profile Control Panel and Switching Box, check the green connector between them as above. Recheck system. If condition persists, try to isolate the problem to one component (and replace it as needed):

Isolate Power Source issues: Disconnect the key-switched 12V wire and connect it directly to the battery. Run the system. Proceed to next step if problem persists.

Isolate Grounding issues: Measure the resistance from the green ground connection on the interface cable to the battery’s negative terminal. This should be less than 1ohm. Run the system. Proceed to the next step if problem persists.

Red lamp pushed part way out of control panel. This could result in the relay operating inconsistently or not operating at all.

Possible Cause
Factory assembly defect.

Corrective Action
Back cover could be removed and the tab on the red lamp that is touching the relay could be bent carefully so that the Tab no longer interferes with the relay.

Power fuse blows.

Possible Cause
Short to ground in the control circuit.
Corrective Action
Locate and correct short or replace control panel.

Possible Cause
Incorrect fuse.
Corrective Action
Install correct OEM fuse.

Possible Cause
Incorrect wiring.
Corrective Action
Repair wiring according to wiring diagram.

Oil level is too low.

Possible Cause
Excessive oil carry-over
Corrective Action
Inlet valve.

Possible Cause
Parked on uneven ground
Corrective Action
Park on level ground and check level again. Add oil as necessary. Check level at the sight glass and add as necessary

Frequent compressor over-temperature shutdowns.

Possible Cause
Discharge temperature probe failure.
Corrective Action
Replace probe if defective.
Follow Test Procedure 2

Possible Cause
High ambient temperatures.
Corrective Action
Reduce duty cycle.

Possible Cause
Low oil level.
Corrective Action
Check oil on level ground, add as required.

Possible Cause
Restriction in the compressor oil lines.
Corrective Action
Check for kinked or pinched oil lines.

Possible Cause
Compressor oil filter plugged
Corrective Action
Replace oil filter.

Possible Cause
Heat exchanger not functioning or is fouled with deposits.
Corrective Action
Remove and clean or replace heat exchanger.

Possible Cause
Engine cooling system failure (engine temperature will be high).
Corrective Action
Correct engine cooling problems.

Possible Cause
Engine fan clutch slipping.
Corrective Action
Replace if defective

Possible Cause
Oil temperature probe failure.
Corrective Action
????

Drive belt is broken or missing.

Possible Cause
Alignment problems
Corrective Action
Install new compressor belt

Belt squeals when compressor switch is activated.

Possible Cause
Worn Belts
Corrective Action
Check alignment of pulleys.

Possible Cause
System is under pressure.
Corrective Action
Allow 10 seconds for blow-down.

Possible Cause
Blow-down valve not working.
Corrective Action
Replace blow-down valve.

Possible Cause
Improper belt tension.
Corrective Action
Check belt tensioner.

Possible Cause
Belt is glazed.
Corrective Action
Replace belt.

Low air pressure.

Possible Cause
Air flow is too high.
Corrective Action
Reduce consumption.

Possible Cause
Throttle control set too low
Corrective Action
Increase maximum RPM settings

Possible Cause
Pressure regulator valve set too low.
Corrective Action
Increase pressure by adjusting pressure regulator valve.

Excessive air pressure.

Possible Cause
Pressure regulating valve set too high.

Corrective Action
Reduce system pressure by adjusting pressure regulating valve.

Oil blows out of compressor air filter on compressor shutdown

Possible Cause
Shutting the engine off while running at high speed.

Corrective Action
Allow engine to idle-down before shutting down the compressor. Turn off any air tools before shutting down compressor.

Oil drips from clutch after shutdown.

Possible Cause
Seal leaking.
Also visit Ogura for additional clutch troubleshooting.

Corrective Action
Contact the nearest dealer to replace gearbox input shaft seal.

Excessive oil in the air.

Possible Cause
Failed coalescing separator element.
Corrective Action
Replace element.

Possible Cause
Clogged scavenge line screen.
Corrective Action
Clean or replace parts as required.

Possible Cause
High oil level Poor fit between coalescing filter and tank – lack of seal at O-rings
Corrective Action
???

Engine RPM excessive on initial startup and during operation.

Possible Cause
Maximum RPM setting is too high.
Corrective Action
Reduce maximum RPM setting of throttle control or reset cable nipple.

Possible Cause
Idle-down pressure is too high.
Corrective Action
Reduce idle-down setting of the throttle control.

Engine RPM stays at base idle when compressor runs.

Possible Cause
Maximum RPM setting too low.
Corrective Action
Test and correct connections

Possible Cause
Idle-down pressure too low.
Corrective Action
Adjust throttle controls.
Test and correct connections.
Replace throttle control.

Engine RPM over-revs when compressor is activated.

Possible Cause
Throttle controls not connected properly.
Corrective Action
Increase maximum RPM setting of the throttle control or reset the cable nipple.

Possible Cause
Throttle control not setup properly.
Corrective Action
Increase idle-down setting of the throttle control.
Check and correct connections.
Adjust high idle screw.

Engine RPM does not return to base idle.

Possible Cause
Wiring fault.
Corrective Action
Check and correct wiring according to wiring diagram.

Possible Cause
Throttle not properly adjusted
Corrective Action
Adjust idle down screw.

Engine RPM stays at maximum whenever the compressor is running

Possible Cause
Idle-down setting is too high.
Corrective Action
Reset idle-down pressure.

System is very noisy during operation

Possible Cause
Defective idler or tensioner bearings.
Corrective Action
Locate the source of the noise and replace the appropriate part.

Possible Cause
Locate the source of the noise and replace the appropriate part.
Corrective Action
If the noise is coming from the compressor, replace the unit.

Possible Cause
Vehicle hood is open.
Corrective Action
Noise levels can be reduced by closing the hood while operating the compressor.

Engine stalls on activation of the system

Possible Cause
The compressor or clutch is damaged.
Corrective Action
Make sure that the system has no residual pressure by venting the tank. Remove the drive belt and spin the outer part of the compressor clutch. It should spin freely. Using a socket and ratchet on the center bolt on the compressor clutch, turn the compressor clockwise. If the compressor will not turn, it has internal damage.

Engine stays at base idle

Possible Cause
The throttle control is not increasing engine speed
Corrective Action
Electronic throttle controls, Follow Test Procedure 3
Pneumatic throttle controls, Follow Test Procedure 4

Belt squeals on startup

Possible Cause
There is residual air pressure in the system
Corrective Action
Residual air pressure in the system will cause the compressor to stall. Vent air pressure and test again.

Possible Cause
There is insufficient belt tension
Corrective Action
The belt tensioner may be damaged and is not applying sufficient tension to the belt. Compare the tension of the VR7000 belt with the OEM belt or test the tension with an approved tension gauge. If the belt seems too loose, replace the tensioner.

Possible Cause
The drive belt is damaged
Corrective Action
If the belt is cracked, glazed or is missing pieces, replace the belt.

Clutch slips and is damaged

Possible Cause
Insufficient voltage to the clutch
Also visit Ogura for additional clutch troubleshooting.
Corrective Action
If the clutch does not receive battery voltage, there will be insufficient magnetism developed and the clutch will not engage correctly. This will cause instant destruction of the matching surfaces, as they are not lubricated and cannot withstand the friction.
Follow Test Procedure 5

Engine speed is too high

Possible Cause
Incorrect adjustment of the throttle control
Corrective Action
The cable nipple is not positioned correctly or the electronic control is not adjusted correctly.
Follow the procedures in your Owners Manual

Engine speed is too low

Possible Cause
Incorrect adjustment of the throttle control
Corrective Action
The cable nipple is not positioned correctly or The electronic control is not adjusted correctly.
Follow the procedures in your Owners Manual

Engine stays at base idle

Possible Cause
The throttle control is not increasing engine speed
Corrective Action
Electronic throttle controls, follow Test Procedure 3
Pneumatic throttle controls, follow Test Procedure 4

Engine will not return to base idle

Possible Cause
Throttle operation has interference
Corrective Action
On pneumatic throttle controls, check the operation of the throttle

Air pressure is too high

Possible Cause
Incorrect regulator settings
Corrective Action
Follow the procedures in your Owners Manual

Possible Cause
Defective regulator
Corrective Action
If adjusting the regulator does not have any affect on pressure and engine speed is correct, replace the regulator.

Excessive oil in the air

Possible Cause
Operating angle of the vehicle is excessive.
Corrective Action
Maintain a level operating position no greater than 10 degrees from the horizontal

Possible Cause
Oil level is too high
Corrective Action
Check the oil level at the tank and drain sufficient oil to correct the level.

Possible Cause
Coalescing element is defective
Corrective Action
Follow the repair procedures to replace the coalescing element.

Possible Cause
Scavenge line is plugged
Corrective Action
Clear or replace the line. Check the scavenge line filter for contamination.

Oil blows out of the air filter on shut-down or the air filter is always wet with oil

Possible Cause
Shutting down the engine before returning to idle.
Corrective Action
Turn the compressor off FIRST and allow the engine to return to idle.

Air pressure is too low

Possible Cause
Insufficient air flow or incorrect regulator settings
Corrective Action
Follow the procedures in your Owners Manual

Possible Cause
Defective regulator
Corrective Action
If engine speed settings are correct and adjusting the regulator has no effect on pressure, replace the regulator.

Frequent relief valve operation

Possible Cause
Air pressure is too high
Corrective Action
Follow the procedures in your Owners Manual

Possible Cause
Defective relief valve
Corrective Action
If pressure settings do not exceed 200 psi, replace the relief valve.

Fuse always blows

Possible Cause
Short to ground in the control circuit.
Corrective Action
Recommended fuse is 20 Amps. Check the blown fuse to make sure that it was a 20 Amp fuse. If a 20 Amp fuse blows repeatedly DO NOT replace it with a larger fuse.

Possible Cause
Incorrect fuse
Corrective Action
Locate and correct short or replace control panel.

Possible Cause
Incorrect wiring.
Corrective Action
Repair wiring according to wiring diagram.

Possible Cause
System electrical problems
Corrective Action
????

Red lamp pushed part way out of control panel. This could result in the relay operating inconsistently or not operating at all.

Possible Cause
Factory assembly defect.
Corrective Action
Back cover could be removed and the tab on the red lamp that is touching the relay could be bent carefully so that the Tab no longer interferes with the relay.

Intermittent operation

Possible Cause
Poor wiring connections
Corrective Action
Faulty control unit or throttle control
Defective temperature probe
Defective pressure transducer

No response from the vehicle throttle

Possible Cause
Faulty connections between the electronic throttle controller and the foot pedal
Corrective Action
Remove all of the connectors.
Visually check the condition of the pins and sockets.
Insert the connectors firmly, making sure that the latches on the connectors close.