It seems like the air compressor has been running for far too long. You watch it for awhile, then realize that something is wrong. The air compressor will not shut off!
Is this a problem with your air compressor? Read on… the reasons why an air compressor will not shut off and remedies for that problem follow.
There are a number of scenarios that come to mind that might cause this compressor problem and they are explained fully below.
One of the issues when the air compressor will not shut off is that the tank pressure (displayed on the tank pressure gauge) never reaches the cut out setting to allow the pressure switch to trip to off which normally results in the pressure switch cutting power to the compressor motor and the air compressor shuts off.
On other compressors the tank pressure might reach a certain pressure level – also displayed on the tank gauge – and then the pressure in the tank stops building. The result? Again, the tank pressure never reaches the air compressor cut out pressure setting and the compressor cannot shut off.
A third scenario is when the compressor runs, the tank pressure rises, then passes the normal cut out setting, and the compressor continues to run until the pressure relief valve cracks open to vent the pressure.
Here’s what’s involved with all these scenarios about why an air compressor will not shut off.
The first thing to do is watch the tank pressure gauge as the compressor is running. It should rise steadily to the normal cut out pressure setting of the particular compressor.
Air Compressor Will Not Shut Off – Is Gauge Broken?
If the tank gauge does not rise at all, that may be a symptom of a failed gauge, though this is unlikely. Still, if the regulator gauge works, swap it with the tank gauge, with the tank empty and the power off to the compressor.
After swapping, start the compressor again. If once again the tank gauge doesn’t move at all, then it’s likely not the gauge that is the problem, it is that the pump is not delivering air to the tank, and the tank pressure level cannot increase to cut out as a result.
Next, Check To See If Compressor Pump Is Actually Pumping
If the tank gauge is not moving at all, and the compressor motor is running, can you tell if the pump is pumping?
If the compressor hasn’t been running long enough for the pump to get too hot, or if it has, turn the compressor off and wait for it to cool, and then, resting a hand lightly on the top of the pump while the compressor motor is running should indicate if the pump is running and it’s not just the compressor motor running ineffectively.
If the pump isn’t running, then check any belts that connect the motor to the pump, or, if the compressor is direct drive, ensure that the coupling to the pump drive is still secure. If not, tighten it or tighten the belt if belt driven. Test again. If the pump still will not run it is likely that it has undergone a serious mechanical failure, and it’s time to take it apart to see what’s what. More on this farther along.
Tank Pressure Rises And Stops Before Cut Out Pressure Level
If the tank pressure rises and stops before it reaches the normal cut out pressure setting, yet the compressor motor and pump keeps running, that is a strong indicator that the pump itself may have a problem.
Pull the pump air intake filter and be sure that air is being pulled into the intake, and that air is not blowing back out. If air is escaping there, you’ll need to open the pump up and replace the intake valve.
Pull the line that runs from the pump to the tank and try, with a gloved finger, to try and stop the air flow out of the pump while it is running. If you can do this, odds are good that it’s the high-pressure valve that has a problem. Again, it will be necessary to take the pump apart to check.
If the compressor is oil lubed, and a lot of air is blowing out of the oil fill tube, that points to badly worn piston seals, and yes, you will need to disassemble the pump to effect repairs.
Compressor Does Not Stop And PRV Opens
If the pressure in the tank reaches the normal cut out setting and the compressor motor does not stop, then the pressure in the tank will continue to rise until the pressure relief valve lets go, venting the over pressure, and defusing a dangerous situation.
If this is happening with your air compressor, you should not use it again until the problem is corrected.
The fix is, typically, a replacement pressure switch. The pressure switch is supposed to cut power to the compressor motor when the cut out pressure setting is reached. That the air compressor will not shut off then, yet continues to run and the pressure in the tank continues to rise, indicates that the pressure switch has not tripped to off.
There is a diaphragm in the switch that may have failed, or, perhaps the points in the switch have fused, the latter often being caused by a short in the compressor wiring.
Regardless, if the compressor reaches a pressure level that blows the PRV, get the pressure switch looked at, fast. Preferably before you use the compressor again.
These are the main scenarios why air compressors will not shut off. If these don’t help, feel free to leave a question below.