What should I expect?

Hey everyone, it’s been a while since I’ve been on here, and I kinda wish that I wasn’t returning on this part of the forum, but oh well. Back in November, after over four beautifully loud years with my horn setup, my compressor started to take longer and longer to finish it’s job and I don’t think I was getting long enough into a honk before it switched back on. One night, after a semifinal win (I’m a high school football coach), I wanted to celebrate by giving the world a wake up call. I pushed the button and what came out of the horns can only be described as a baby ferry horn. It was like Morgan Freeman letting out a long sigh, only not as interesting. I pulled over and popped my trunk to pull my release valve, thinking that if I manually brought it to below the compressor’s activation point, it would fix itself (sounds stupid, but hindsight is 20/20). After letting out a very weak burst of air, nothing happened. It’s been like that to this day, but I just called HB and they sold me a replacement pressure switch, which should be arriving sometime next week. I’m pretty sure that it’s the switch that’s giving me grief, but I wanted to ask you guys if you’ve ever heard of or experienced anything similar to my situation, what you did to solve the problem, and if a moron who thinks that an air compressor can fix itself can repair the issue without losing too much of my blood supply. Thanks everyone!

I would use a voltmeter to see if the compressor is getting power with no air in the tank.
If not, the pressure switch isn’t doing its job.
If the compressor is getting power and not running, you have yourself a different problem.

I used one and it showed that power was going into the relay, but wasn’t making it back out. Was ordering a new switch the right move?


Also, check the ground to the relay. Corrosion can creep up and bad ground would cause it not to work.

Make sure the trigger wire actually has power too.

The fact that the compressor is running longer and longer sounds more like a classic broken check valve (i.e. leaking) which means your air pressure will take longer to build and will eventually drain back out again. If that’s the case though, you should hear the compressor start up all the time.

When’s the last time you’ve checked for fluid in the tank and lines? It could be that you’ve got more than one issue. Perhaps a broken pressure switch and a broken check valve. Both would wear out if they’re exposed to water and perhaps freezing conditions as well.

I have not checked for fluid in the tank/lines. Not sure how I’d go about doing that. Also, I did notice that on particularly cold mornings, the compressor would start up when I turned the car on, but I don’t know if that’s normal or not. I wasn’t the one who installed it (trust me, we’re ALL a lot safer because of it!), so I have no idea how to swap out a new pressure switch. I was told to just unscrew it and reconnect the wires, which sounds a little to good to be true. Do I need to disconnect the battery, need any specific tools, etc? I’d really like to learn more about how my car and train horn work, but from what I’ve gathered, that requires a good amount of trial and error, which I can’t really afford right now. Thanks for the continued help!

Compressor starting when it’s cold is normal. It’s because as the air cools, it is more dense and has less pressure.

Now for the fluid, it will accumulate generally in the lowest part of the tank. That’s why you should always have a tank drain valve at the base of the tank so you can periodically empty it. It’s also the main reason why you don’t want your compressor inlet line or the pressure switch on the bottom, because that means they’re exposed to that water.

Water will collect inside the lines as well, but generally in very small amounts, plus it will tend to blow out when you run the compressor or the horns. When water collects in the check valve it can cause damage to the internal parts such as the seals, especially when it freezes (since water expands as it freezes)

To check your tank, simply open the lowest port. That will drain it. You won’t need to check your lines. Just run some air through them.

To replace a check valve, you’ll need to simply swap it out. Make sure you use a thread sealant or a teflon tape when you put in a new one. Obviously the valve only flows one way, so make sure you have it pointing the right way. See here if you want to find out more on how the check valve and compressor work together:

On the electrics side, the pressure switch is nothing special. It’s basically the same as any other ON/OFF switch. The switch will be in the ON position when the air pressure is lower than the rated pressure of the switch. When the switch reaches its rated pressure, the switch will go to the OFF position. The wires that are connected to your pressure switch basically carry a 12V current through to another switch called a solenoid. It controls the on/off function for the compressor.

If you bought a Hornblaster kit (e.g. the Shockers), you will probably have one of these:

It’s basically a combination of a pressure switch and the compressor relay all in the one housing. It’s a little more confusing since you have the wires for the compressor, the earth and the pressure switch all coming out of it.

To replace it, you’re best to disconnect your negative terminal on your battery first, because there is a power wire going into this unit and you won’t want to risk shorting that out while you do your work.

Basically, just unscrew the unit by turning the whole assembly. Watch closely where the casing joins the brass stem. You can do this by hand, but if you notice you’re turning just the case and not the stem, then undo the switch using a spanner at the base of the brass stem.

Once it’s out, just simply thread in the replacement unit. B careful not to over tighten it (just hand tighten; you can check for leaks later).

Disconnect the wires from the old switch and connect them to the new one. Do these one by one so you don’t get them mixed up. Reconnect your battery lead and turn on the system. The compressor should fire up and charge the tank.

To check for leaks, just grab a spray bottle with some strong detergent & water mix and spray that on the fitting once the tank is charged up. Any air leaks will show up as bubbles, meaning you’ll have to tighten the switch a little more.

If you have a small pressure switch such as this:

then you will just have two wires going into it. One side is 12V positive and the other goes to the compressor relay (on the trigger pin). Again, just a simple matter of swapping it out and reconnecting the wires (won’t matter which way round you connect the wires).

If anything seems unclear, let us know.

I’m really sorry, but when it comes to this sort of thing, I’m REALLY pathetic. I didn’t install the horn kit myself, but I want to do this on my own. The new PS just arrived and I’m already completely lost. I think I already asked this, but I want to be double-sure. Do I absolutely need to disconnect the battery while switching out the new PS? I only ask because I’ve developed an uncanny ability to shock myself, over and over and over. I’ve attached a couple pictures of my setup (which somehow uploaded at a weird angle), hoping that you’ll be able to give me a little more help. I don’t know how to reconnect wires yet, so if someone can give me a one or two sentence tutorial, that would be awesome. Thanks again for the help!

P.S. If we ever cross paths, I’ll buy the first round :smiley:

Also, here is the switch that just came in the mail.

^^Haha my original post… Now that I see your pics - you don’t have a relay or trigger wire.

First thing I would do is check the ground on the compressor. Take it off & make sure it has bare shiney metal to bare shiney metal. Use sand paper if necessary.

When you put it back on if it still doesn’t work, proceed with changing out the pressure switch. It never hurts to disconnect the battery. Your wire wouldn’t directly shock you, but it could arc to any bare metal (ground) if it touches it.

Now I see what you’ve done. No relay - just a pressure switch. Power going in and no power going out means the switch is off , or an incomplete (broken) circuit, … or bust.

It sounds like you have permanent power on your switch line, so YES, disconnect your battery terminal to be on the safe side before you do your swap.

The switch you bought should be OK. You just hook those two wires coming out of it into the red power line. So basically if you follow the wire it should run like this:
POWER (Red wire coming from battery) -> into the PR.SW. -> then back out to the COMPRESSOR (on the Red Power Wire) -> and out of the compressor to EARTH (Black Wire).

If you need a wiring diagram let me know.

BTW… if you have a multimeter, do a continuity check on the switch (i.e. hold the probes against the switch contacts). Here’s a pic of a standard multimeter:

If you have continuity (i.e. electrical flow) then the switch isn’t your problem.

Also,… can you just confirm what model compressor you have there.

I’ll see if I can find the exact model number tomorrow. I only have the kit number (HK-S4-V228).

OK, that’ll be a Viar 280 then. I generally don’t think it’s a good idea to just use a pressure switch in line with a compressor without a relay, but on that model you should get away with it.

See if you can do the checks That ear2ear and I suggested, then let us know what the outcome is.

Wait, ear2ear wants me to remove/unbolt my compressor from my trunk?

Nah… what he’s saying is to check your ground/earth wire to make sure it’s not stopping the current from flowing. Did you have a multimeter?

I don’t, but the place that installed it (which is where I went a few days ago) did have one. He was the one who told me that one of the wires was inactive.

Oh well… not to worry. Just swap out the switch and give it a test. If you’re not sure about your wiring, post a pic of what you’ve done before you fire it up.

You, sir, are a gentleman and a scholar. I’ll let you know how it goes! We start work at dawn…after coming down off of my Valium and Nitrous from the dentist lol.

^^I forgot about this part…

If there was power on one side of the pressure switch and not on the other - and there was little to no air in the tank - it’s the pressure switch.

So probably no need to check the compressor ground.