Can't get compressor to shut off

I bought what I believe was an S4 kit back in 2009-2010. This is the problem I am having - The compressor will continue to fill the tank with air until the emergency blow off valve goes off. I’ve changed the pressure switch already pretty recently. The other strange thing is when I turn my truck off, take the key out, and open the door (which cuts off all accessory power) The compressor continues to pump air. It did not do this before.

My question is this-should I replace the pressure switch and the relay to see if that works? Is there anything else that I should replace? Could something in the compressor have gone wrong that doesn’t allow it to shut off?

Any input would be great because for the past two years I’ve just had the fuse pulled out and I haven’t been able to use the horns and I dearly miss them.


What happens when the wires are removed from the pressure switch?

You know I haven’t tried that. I will try that out. Any other suggestions?

Do you have that all-in-one blue unit from Hornblasters (i.e. pressure switch & relay), or a single pressure switch and separate relay?
Sounds to me like it could be a faulty relay (i.e. one that is sticking in the ON position)

^^^^^^^^^^^ I am with DBO, check your Relay, 9 times out of 10 its your relay.

im with them^^^^ i had the same problem as you. new relay fixed it for me

Is there anything else that I should replace?

Welcome to the forum. If the compressor continues to run after the pressure switch and relay have been replaced or verified as good then it’s getting power elsewhere which is highly improbable.

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