# Compressor won't shut off. Bad relay?



## reynolds9000 (Oct 16, 2003)

I'm having an issue where my compressor won't shut off, however my tank is filling. I have a leak that drains the tank over a 24 hour period so the compressor always turns on when I start the car in the morning, and used to always takes 5 minutes to fill from 0psi to 145psi. Now it takes 10-15 minutes. At first I thought I might have a sticking check valve but when I went out for a drive last night, I emptied the tank to 110psi, the pressure switch triggered the compressor to turn on but never shut off. It ran for 20 minutes before I was finally able to pull over and disconnect the power to the pressure switch. 

Im running a Viair 110-145 pressure switch, a 400c Viair compressor and a 40amp Viair relay. I have an SMC NK2000 check valve. 

I'm on the way to run some errands and won't be home to do some troubleshooting until later. I was hoping to get some suggestions on what it might be in the meantime.


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## reynolds9000 (Oct 16, 2003)

My first plan is to remove and take apart the check valve to clean it. 

How can you test to see if the relay is bad? Is there a way to check for a faulty pressure switch?


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## MechEngg (Jan 13, 2009)

Do you have a pressure gauge on your tank to visually watch that it exceeds 145psi? Or is it not filling to 145psi? Big difference there. 

If your compressor is taking longer to fill but fills then you very well might have a piston ring issue. If it never reaches 145psi that is an even bigger indicator of piston ring issues 
If your compressor is exceeding 145psi then you probably have a relay sticking (just remove it and test the 85&86 leads across a battery to hear if it clicks open and closed as you add and remove power from across it) or your pressure switch isn't functioning properly.


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## reynolds9000 (Oct 16, 2003)

I don't have a gauge on the tank, but that would be very helpful right now. I'll definitely be adding one in the future. As far as the compressor goes, it's not making any abnormal sounds but then again I don't know if it would should the ring go bad on the piston. 

The 400c has a max pressure of 150psi and the tank is definitely filling and pressurized enough to lift the car at the normal speed it always has. I just don't know if it's actually hitting 145psi or not.


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## MechEngg (Jan 13, 2009)

First thing i would do is run out and grab a gauge and determine what pressures it is able to achieve. Without that we don't know if it is actually hitting the 145psi pressure switch or not. It is possible that you are only getting 100psi or so and you can still raise the car like that, may be a bit slower if you are running 3/8" lines.


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## rgarjr (May 19, 2012)

U need to take care of that huge leak you have which is putting more wear on your comp.


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## reynolds9000 (Oct 16, 2003)

The leak only started happening a few weeks ago. As its not my daily driver I really don't know exactly how long it takes to drain from full pressure to 0psi but I assume that it's about 25 hours. I suspect it's the check valve as research has shown that the SMC AK2000 valves can leak between the head and the body. I just took it apart completely and cleaned it with q-tips and rubbing alcohol. It's all good to go now. However, MechEngg was right, my piston ring totally crapped out and ruined the piston wall. The piston itself is pretty chewed up as well. I know I can buy rebuild parts for it but I went ahead and bought a new compressor since I was able to find out semi locally and I need it fixed ASAP. 


Here is the carnage. The entire circumference of the piston wall looks like this. 










You can see the right side of the piston has no ring left on it. 










I really hope that this isn't a common thing for ViAir compressors. I was always under the impression it was a high quality brand. I've had this compressor for 2 years but I don't daily drive the car so it's not like it runs multiple times a day, everyday.


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## MechEngg (Jan 13, 2009)

Ask me how i knew what your problem was  

I have heard of this happening on viairs that have had their check valves fail before. When the check valve fails shut the air in the cylinder has nowhere to go and gets over pressurized and heats up to very high heat and can then destroy the rings under the high heat and pressure. I'm not sure what happened to mine though because my compressors always run very very cold (hold it in your hand while it is running) and my check valves have always been good. Maybe just luck of the draw


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## reynolds9000 (Oct 16, 2003)

I saw your thread when that happened to your compressor. That really sucks...especially since its an AZ. Those are bad ass comps and not cheap!

I did have a faulty check valve (viair) that I replaced with an SMC so that definitely could have been a contributing factor.


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## Niagara_V_Dub (Sep 25, 2007)

Holy compressor carnage! This is why the viair check valve never saw my car, immediately swapped it with a SMC before I ever installed anything. 

The reason is cause of this awesome forum. 

Also do you have a shrader valve for manual tank inflation? If you do you could always use a digital pressure tester. If you don't have one, I would install one for sure.


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## reynolds9000 (Oct 16, 2003)

I have a 4 port tank but I have one in my tool box that I can swap in at a gas station should I ever need to do that. I'm going to rebuild this compressor and keep it as a spare. It just need a new reed valve on the head, new cylinder wall and a new piston assembly. About $100 in parts.


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## MechEngg (Jan 13, 2009)

I got my whole head assembly replaced under warranty from AZ, they have 2 year warranty's. How old is your viair?


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## reynolds9000 (Oct 16, 2003)

It was 2 years old, but ViAir only has a 1 year warranty. If the check valve had never gone bad, i might have gotten a lot more life out of this comp. I've read on a lot of mini truck forums that guys have been getting 4-5 years out of ViAir compressors and they tend to run much larger tanks than us VW guys. 

A 2 year warranty is a big upside to the AZ comps. If I continue to have issues with ViAir i might make the switch to an OB2. In the meantime, i'm going to rebuild the broken compressor and keep my fingers crossed that the same thing doesn't happen to my new one.


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