OBA Pressure Switch Question

[tigger]

Finishing up mounting my Viair compressor under the hood. I got a pressure switch for it to control when the unit shuts off.

My question is where to wire it. Can I wire it inline on the power wire for the compressor, (much easier) or would I have to place it before the relay (much more difficult)?

I can't find any indication on how much current it will handle and the instructions are worthless.

Vixen Horns VXA7115 90-115 PSI Pressure Switch VX-Pressure Switches VXA 7115

https://www.hookedontronics.com/images/horns/manuals/VXA7115.pdf

 

[wfo9]

Sort of confused why it would be a problem in front of the relay...

You have a switch in the cab right? The pressure switch terminals should be on that line going to the relay. They can almost never handle the amp draw of the motor.

 

[tigger]

Sort of confused why it would be a problem in front of the relay...

You have a switch in the cab right? The pressure switch terminals should be on that line going to the relay. They can almost never handle the amp draw of the motor.

It's a wiring problem. The location of the pressure switch is along the path of the power wire. To get inline in front of the relay I have to run 2 more wires back into the cab and pull the dash apart again.

I have seen wiring diagrams both ways, but found one specifically from Viair and it shows going before the relay so I think I will go that route. Was just trying to save an extra hour of work vs. 5 min.

 

[rigtec]

Finishing up mounting my Viair compressor under the hood. I got a pressure switch for it to control when the unit shuts off.

My question is where to wire it. Can I wire it inline on the power wire for the compressor, (much easier) or would I have to place it before the relay (much more difficult)?

I can't find any indication on how much current it will handle and the instructions are worthless.

Hi tigger,

I just took a look at your air pres. switch and quite a few 100 to 120 psi air compressors to learn some conventional (UF) electrical parameters. Here's what you could do. The compressor (based on those I auditioned) will draw a max of 15A/12V @120 psi. You can verify that by connecting it directly to your battery, and use a DC (inductive) clamp meter to check this compressor's full load draw at 120 psi.

Next is the Pres control switch. It's made to cut-in @ 90 psi, and cut-out at 110 psi; for very tight parameter pres control. The pres switch should have an electrical rating of 12 (or 24) volts and a current capacity of 20 amperes. So... Just run a HOT 8-ga cable with a 30A in-line fuse from the 'POS' side of the battery to one terminal of the pres. switch (power in).

Then run another 8-ga line from the other pressure switch terminal (power out) to the POS of the compressor. Now run a short 8-ga cable from the NEG terminal of the compressor to a good ground source under the hood; it doesn't have to go directly to the neg post on the battery, it's best to keep that GND line as short as possible... that's it! Just give it a test before you do your install to make sure that it all works out because some of the data was sourced from different websites!

rig

 

[rigtec]

If you prefer using a relay to trigger the ON/OFF operation of the compressor feel free to do so. The pres. switch can trigger the relay coil; which in turn will energize the compressor, it doesn't really matter. ...Be nice to have of the entire compressor kit just some visual support, but if what I posted earlier works out than that's no longer necessary!

 

[tigger]

Hi tigger,

I just took a look at your air pres. switch and quite a few 100 to 120 psi air compressors to learn some conventional (UF) electrical parameters. Here's what you could do. The compressor (based on those I auditioned) will draw a max of 15A/12V @120 psi. You can verify that by connecting it directly to your battery, and use a DC (inductive) clamp meter to check this compressor's full load draw at 120 psi.

Next is the Pres control switch. It's made to cut-in @ 90 psi, and cut-out at 110 psi; for very tight parameter pres control. The pres switch should have an electrical rating of 12 (or 24) volts and a current capacity of 20 amperes. So... Just run a HOT 8-ga cable with a 30A in-line fuse from the 'POS' side of the battery to one terminal of the pres. switch (power in).

Then run another 8-ga line from the other pressure switch terminal (power out) to the POS of the compressor. Now run a short 8-ga cable from the NEG terminal of the compressor to a good ground source under the hood; it doesn't have to go directly to the neg post on the battery, it's best to keep that GND line as short as possible... that's it! Just give it a test before you do your install to make sure that it all works out because some of the data was sourced from different websites!

rig

That's what I was thinking of doing. It's a Viar portable kit that I am adapting to a permanent mount.
VIAIR Corporation - 400P Compressor (P/N 40043)

It does have a max 30 amp draw and a 40 amp inline fuse. I was just going to use the wiring it came with, clip off the battery clamps, clip the ground wire near the compressor to ground it and splice the pressure switch inline on the positive side. But if you feel the switch is rated at 20 amp, then I need to take it to the relay as Viair suggests.

- 12-Volt / 24-Volt
- Permanent Magnetic Motor
- Duty Cycle: 33% @ 100 PSI
- Max. Working Pressure: 150 PSI
- Max. 12V Amp Draw: 30 Amps
- Max. 24V Amp Draw: 15 Amps
- Ingress Protection Rating: IP54
- Dimensions: 11.5"L x 6.0"W x 7.5"H
- Net Weight: 10.40 lbs.
- Power Cord Length: 8 ft.

 

[96r50]

The ARB wiring harness that ships with their compressors has the pressure switch on the low amp side of the relay, not in line with the compressor motor. Those switches likely aren't related for many amps.

 

[tigger]

I went ahead and wired it on the front end of the relay as it really should be. Works perfectly.