The pressure switch is responsible for turning on your compressor when your air pressure is too low and turning your compressor off when your air tank has reached the designated pressure. Naturally, when the pressure switch fails it will either not turn your compressor on or not turn your compressor off.  

If your compressor won’t turn on, check your wiring first. You could have just blown a fuse or have a weak/poor ground. If you have recently installed your kit, it's more than likely something simple with the install, so ensure you double-check the wiring using our instructions and wiring diagram to make sure all of your connections are good. This includes checking your in-line fuse to make sure that it didn’t blow. If all of your wiring is correct, the next step is to verify that the compressor turns on with direct power.

We can do this by taking the compressor directly to our car battery (or another 12v battery) to test with or by connecting 12-volts directly to it. Take the compressor to your battery or 12-volt source and touch the red wire to the positive terminal. With that connected, ground the black wire to the negative terminal on the battery or the vehicles frame. Upon making this connection, the compressor should begin to run immediately. If it does not, the compressor has likely failed and will need repairs in order to function again.

If your compressor will not shut off and your pressure gets high enough to activate your safety blow-off, the very first thing you want to do is disconnect the compressor from power. You can remove the fuse from the fuse holder to stop the compressor from running. Your compressor not turning off is much worse than not turning on, because if left running you could blow your fuse or even permanently damage your compressor because it is being forced to work much harder than it was designed to, therefore pulling more power from your battery. Fortunately, replacing your pressure switch is easy and doesn’t cost very much if out of the warranty period. Below are some of the common pressure switches that are direct replacements for the ones we use in our horn kits and onboard air systems.  

• The sealed pressure switch w/ leads is the ideal replacement for any 127H or 228H system.
• HornBlasters Weatherproof pressure switches are the best option for kits mounted underneath your vehicle, where it will be exposed to the elements.

Should you find that the compressor or pressure switch has failed, each component does carry a 1-year warranty through the respective manufacturer. For instance, Viair offers a 1-year manufacturer's defect warranty for all of their compressors. If you have a Viair compressor that was purchased less than 1-year ago, you can get the warranty process started by reaching out to HornBlasters. Hornblasters requires proof of purchase to authorize a warranty claim on your compressor. Please reach out to us by email at Sales@hornblasters.com for more information, or to get the warranty process started.

This guide explains why a compressor may be blowing fuses, covering common causes such as worn check valves, exposed wires, poor connections, or faulty carbon brushes, and how to troubleshoot them safely.