Pressure Switch for Compressor

[firemediceric]

My wife, bless her heart, bought me some train horns for Christmas.

She went on line and went with a set up/vendor that looked good to her. I may have made another choice, but anyway...

I installed the horns per the instructions. They sounded great and worked well; for a couple of days. The pressure cut off switch that is suppossed to turn off the compressor failed. The compressor kept running driving the PSI up to 200+.

I paid extra and went with an upgraded compressor from the vendor and they sent me a new pressure switch. I installed it today, but once again, the switch failed to turn off the compressor. The first time I tested the set up, every thing worked fine and the compressor shut off at 130 PSI. After that, it didn't work again!

I contacted the vendor to ask if I could have gotten two bad pressure switches out of a bad lot.

His reply was:
"If you have had 2 failed pressure switches in a row then you are using the wrong size wire or something is not right. I suggest that you wire it up without a pressure switch and run it on a manual toggle. after you blast the horns toggle it on for 10-15 seconds then toggle it off. "

I shot back with:
"I am using the ground wire coming off of the compressor and have not supplied any wire of my own. All I have done is taken that wire and put it to the frame for ground with the pressure switch connected in the ground wire.

compressor--------> ground wire-------------> pressure switch------------> ground wire----> truck frame.

Although I follow your suggestion to not use the pressure switch, I would rather have the system working correctly as designed."

Here's the last from the vendor:
"Very very likely that the ground is not a quality ground and if the pump has to "pull" ground through the switch it creates a hot spot in the switch causing it to fail."

So for you experts, what's the verdict? I have the ground wire going to the same bolt on the frame that attaches the chasis ground strap. Have I done something wrong? Has anyone else had this problem?

Thank you

[angus]

Maybe the pressure switch isn't rated to handle the current that the pump motor draws. Get a 30 amp automotive relay and wire it so the pressure switch activates the relay, and the relay switches the pump motor.

[ford390gashog]

You may really want to just get a heavy duty switch. You can use a pressure switch from a standard air compressor. I like to use the Square D brand. You should look at www.grainger.com try part
5B419

[firemediceric]

Originally Posted by angus

Maybe the pressure switch isn't rated to handle the current that the pump motor draws. Get a 30 amp automotive relay and wire it so the pressure switch activates the relay, and the relay switches the pump motor.

I'm not much of an electrician. The addition of the relay means I will need to run another wire, right?

Right now I have a power wire from a switch in the cab going to the compressor. I have a second hot wire going from a switch in the cab to the horns. I have a ground wire from the horns to the chasis and a ground wire running from the compressor to the chasis. That last one is the one that the pressure switch is tied into.

I'll sit down with the relay. Maybe it will be clear to me as I look at it.

[firemediceric]

Originally Posted by ford390gashog

You may really want to just get a heavy duty switch. You can use a pressure switch from a standard air compressor. I like to use the Square D brand. You should look at www.grainger.com try part
5B419

I'll try to take a look at one today. I never thought of using it for a 12 volt application.