So I’ve had my horns for over six months now and haven’t had any problems until this summer. A couple weeks ago, I found my compressor fuse (35A) melted. I assumed it was due to overheating as I just came back from a long vacation and my tank was empty, requiring a long run to refill. I replaced my fuse with the only one I had available (30A) and it ran fine for a few weeks. Just the other day, I realized my horns weren’t blasting loud from low pressure and my compressor wasn’t turning on, checked the fuse and it was melted again. This time, melting the fuse holder as well.
I picked up a couple 30A fuses and a new holder from Auto Zone and wired everything up. The compressor did not start and the pressure switch/ relay was making a buzzing noise. I figured the switch for dead and ordered a viair replacement instead of ordering another HB blue one.
Today I pulled out my meter and started troubleshooting. It seems I am getting good voltage right before the switch on the fused line and shut off line from the toggle, so long as nothing is connected to the pressure switch. Once the pressure switch is connected and the truck is running with toggle switch closed in, my voltage drops to 9 volts on both the fused line and the toggle switch line, and when the switch picks up low pressure on the tank, I get the 9 volts at the power to the compressor line also. My question is, is there somehow a short circuit inside my pressure switch that still allows it to function, but is stealing voltage to the compressor?
My compressor is dead, totally seized. I ran a line straight off the battery to the compressor, and it did not run, it felt like the motor wanted to turn but the compressor wasn’t letting it. The compressor has a good ground, I verified all my grounds too.
Is it normal for a pressure switch to drop voltage on the entire system? Would I be able to warranty claim on the compressor if it failed due to a faulty pressure switch?
Not sure what compressor you’ve got running, but to continuously blow a 30A fuse points to something pretty serious (i.e. generally a short of some kind, and I doubt it was in the pressure switch). I bet the short was internal to the compressor motor since it sounds like that’s burned out.
That drop in voltage isn’t significant if you have a tired battery, but generally isn’t right either. The switches are cheap to replace so if you have doubts, I’d swap that out at the time of installing a new compressor as well.
I have a viair 400C compressor with the hornblasters 110/150 pressure switch. My horn kit is the shocker 540. My truck is gonna be one year old next month and only 13k mileage, it’s definitely not a bad battery, and I checked and had good voltage at my connection to the switch without the switch actually connected. Once connected to the switch, everything dropped to 9volts. It’s definitely the switch.
Lucky for me, I work in a power plant with some people who know a heck of a lot more about electricity than me. I explained the situation to one of our technicians and he said, the switch must have a partial short between some of the internal contacts. He explained that the high resistance I was seeing across the switch with my meter (about 95ohms) is all the proof I need, that if the switch wasn’t faulty, there would be no resistance across it.
The lower output voltage caused by the faulty switch is what killed my compressor. He explained to me that the lower voltage will cause a higher current draw, melting my fuses. He said if it were simply a short circuit, the fuse would not have melted, it would have popped. He also said the higher current draw would have overheated the compressor and eventually seized it. He told me if the compressor had a short to ground, there would be no resistance, and when I checked, there was some resistance across the compressor.
So, yeah, I ordered a new switch, this time I ordered the viair one as I have little faith in the other type now. I also ordered a new compressor. When I ordered the viair pressure switch, I noticed at the bottom of the page it says that this switch is required for warranty claims. I was using the hornblasters blue switch because this is what came with my kit (when the description of the kit states the included switch is the viair one). It will be a shame if I get denied a warranty for using the wrong switch simply because this is what came with my kit.
Thanks for the advice and quick response DBO!
Welcome to the forum.
Make sure the power cable connections are clean. Check the positive power cable for worn or bare insulation, especially where it is near or passes through metal.
Is the compressor ground wire connected to the chassis or directly to the battery?
The connections are clean, and I walked down the positive line as best I could without finding any damage. The compressor is grounded to the chassis, which I considered as a possible problem, but I seem to have good voltage from the positive wire (where it would connect to the pressure switch) when I touch the black lead to my wire going to ground, so long as the pressure switch is not connected to either one of those lines. If the switch is connected, those same two points drop to 9volts.
I spoke to someone at HB yesterday, and I will be sending both the compressor and switch to them as soon as I get the new ones I ordered. They are still within the warranty time, so hopefully they will find that the pressure switch killed the compressor. I wonder though, if they can’t prove that the switch led to compressor failure, would I then have the option to have it rebuilt and returned? I wouldn’t mind having a spare so I don’t ever go this long without my horns again! 
I did take advantage of the down-time though, and I reworked my trigger switch for the solenoid. I had been using a tiny red button, which started to become intermittent, and I was missing some good horning opportunities. So, I pulled the button out (finding a loose, almost broken connection on the back) and replaced it with a light up toggle and the bosch relay so I can switch between stock and shockers. Now, I am anxiously waiting for new compressor and switch to try out my new set-up!!
How Big of gauge of wire are you running? If your fuse is melting that might also mean that your wire is needing to be replaced, do this test, Since you say your compressor is grounded to your chassis I would run a long heavy gauge wire from the Compressor’s Positive Connection (+) and touch the wire real quick to the Positive terminal on your battery directly, (bypassing all of your existing wire) If the compressor fires up and goes “rrrrrrrr”, then the wire you are currently using is not a heavy enough gauge of wire to use on your compressor, there fore you would be required to upgrade your wiring. Just hold the wire onto the battery long enough to see if your compressor is still alive.
I’m rather embarrassed to admit it, but it turns out that the problem was just a bad ground. Having installed many stereo systems on previous cars I owned, I kinda thought this from the start. But once I pulled out my meter, which I have absolutely no experience with, I started chasing a ghost thinking I knew what was wrong and couldn’t be convinced it was anything but. Once I installed the new compressor and pressure switch that I ordered and had the same problem, I knew it had to be the ground. Which explains why the compressor didn’t run when I ran a hard wire from battery positive to the compressor, what I should’ve done was left the positive hooked up the way it was and ran a hard wire to the battery negative to verify good ground. Needless to say, my old compressor is not seized, when I hooked it up directly to the battery after removing it from the truck, it kicked on just fine. I’m going to assume my pressure switch is fine too, but I didn’t bother testing it, just went ahead and installed the new viair one. This is also my first truck and I didn’t realize that the bottom of the bed is not a good ground since the bed floats on rubber grommets, I just wonder how it ran fine since January? Anyway, as hard as it is to admit, this is an obvious case of overthinking, and lack of experience!
Congrats, now you can run both compressors and reduce the fill time.
I’m definitely thinking about it. I looked at the diagrams on HB site for setting up 2 compressors and noticed the larger 60 amp fuse required, would it also require heavier gauge hot and ground wires? I am currently using the 10 gauge that came with my kit.
Might be easier / cheaper to just run another 10ga w/ 30amp fuse.
Just finished my dual compressor install yesterday! I ended up running a 4ga wire with 60a fuse to the bed where it splits to 2 10g wires through the relays and to the compressors with the one switch to run them both. The compressors are also individually fused with 30a fuses. They sound great together, although noticeably louder when they are running, but also noticeably faster to fill!!
I still have yet to wrap the wires and find a better hiding place for the relays, which are currently zip-tied to my cargo rails…lol. But I’m pretty happy with the new look otherwise. Attaching a pic…
Awesomeness.
Soooooo important to re-fuse when stepping down in wire size. Glad to hear you did it right.