The air compressor in our car feeds into an air tank which has the usual pressure cut off switch & a pressure relief valve (PRV).

Recently I noticed that the compressor was continuing to run after it reached the cut off switch's upper limit, & would continue to run eventually causing the PRV to vent.

I assumed that a new cut off switch was needed, bought one & today I fitted it.

BUT it has made zero difference. The compressor still doesn't cut out when it reaches the switch's pre set pressure.

I''m wondering of I have a faulty new pressure switch but also whether there might be some other cause. Can't think of anything else though. The hole the switch screws into isn't blocked.

Any ideas?