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Old 04-29-2014, 09:40 PM   #1
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Join Date: Dec 2012
Posts: 24
Viair 12v 400P-RV Air Compressor review

This is essentially the same review I posted on Amazon about a year ago for the Viair 400P-RV 12V air compressor, available from Amazon here for about $232.

Their website is here - VIAIR Corporation - 12-Volt & 24-Volt Air Compressors and Pneumatic Systems. They have a wide range of portable and built in compressors for various applications. If someone wanted to mount one of their off-road compressors in or under their RV, I think they'd be quite happy with it.

I understand that this compressor is quite expensive, but I wanted something smaller than a 120V compressor to save on basement storage and 12V so I can use it to reinflate my Jeep tires after a beach drive. Finally, I liked having the option of standing well away from the tire while filling them. Exploding tires may be really rare, but they make me nervous and it's worth some of my money to not be there. As they say, your mileage may vary.

The tires on my 29' Class A are 245/70R19.5 and need to be inflated to 100 to 110 PSI, depending on the load, so this is significantly more difficult than a normal 35 psi car tire. My RV does not have a spare tire, so proper inflation is extra important.

I also own a Bon-Aire BA121L 120V compressor with a claimed 2/3 HP I can run with the RV generator, but in testing it on an RV tire ( taking it from 40 to 100 PSI ) I had to quit after 25 minutes ( including 10 minutes of cool down time in the middle, per the manual - 10 minutes rest after every 15min ) at just 90 PSI when the compressor started to smoke.

I replaced it with the Viair 400P-RV. I looked at the 450P, liking the continuous duty, but the 400P puts out more CFM, so the higher fill rate of the 400P seemed like a good idea. Also, it comes with all the parts you need to remotely fill a high pressure, high volume tire which, if it explodes while you're squatting next to it, can easily kill you. If you doubt this, do a search on youtube for "tire explosion" and you'll be convinced.

First impression: It's solidly built and comes with a nice selection of accessories, including two extra air filters, toy and needle attachments, 60 feet of coiled hose in two 30 foot segments and a hand held valve so you can stand well away from the tire while filling. It has an air filler wand and a screw-on filler. All of the fittings look to be standard 1/4in, so connecting the compressor to other lines would be easy. The bag it comes in could be little more rugged, but it's not too bad.

It's also pretty big, with a bulge on the front of the bag for one of the coiled hoses and another on the back for the other hose. In the bag it's actually not that much smaller than some of the smallest 120V compressors that I've seen.

But this is smaller and lighter and runs on 12V, so I can use in my towed Jeep, too.

It has about a 8' long heavy-duty fused power cord with battery clamps. I appreciated this, since I've burned out a cigarette outlet running a lesser compressor in the past. No compressor with any power at all should be using cigarette outlet plugs. According to Viair, the 400P starts out at 2.54 CFM but drops to 1.27 CFM by 100 PSI, at which point it's drawing 26A, far more than you can pull out of a lighter socket.

The compressor has a pressure switch on the back by the on/off switch that turns the motor off when it gets to about 150PSI, so you can leave the compressor on without worrying about damaging it or the hoses by over-pressurizing them if it's not connected to a tire. Nice touch. Additionally, there is a motor protection circuit that will shut off the motor if it gets too hot. If this happens, disconnect the power and let the compressor cool. Once cool, it will operate again.

Viair suggests idling the motor of your vehicle while running the compressor, not only to prevent draining your battery, but to keep the voltage up, making the compressor operate more easily. I ran my tests on my fully charged house battery pack of four 6V batteries, with my RV plugged into shore power.

To test the Viair, I dropped the pressure in one tire from 100 PSI to 40 PSI and connected the compressor. The inline gauge read the same as my TPMS when it wasn't filling, but it read very high while the air is going in. Just pause the filling to get an accurate reading. The compressor seemed to be filling the tire pretty quickly which was good because you have to hold the "trigger" on the valve open to fill the tire. At least it's easy to hold open, so it's not too difficult.

I would release the "trigger" to check the pressure every couple of minutes and in the few seconds it would take for the pressure in the gauge to equalize with the tire, the pressure switch on the compressor would shut it off. It would kick right back on as soon as I continued to flow air into the tire. Nice feature.

About 7 minutes after I started ( probably about 6:30 in actual compressor run time, with several pressure checks on the tire ) the tire was at 100 PSI and I stopped the test. This is significantly less than the listed duty cycle, which means it could have run longer if it needed to.

I lost a little pressure taking the filler off the tire and putting my pressure sensor back on, but when I turned my tire pressure monitor system on it said the tire was at 98 PSI. That's pretty close to what the gauge read.

The cylinder head on the compressor and the air line were hot to the touch, but the motor exterior was just moderately warm. I had to let it sit for about 10 minutes before I was comfortable putting it in the bag.

I'm pleased that it can fill a large tire to a high pressure with some reserve capability left over. It's not cheap, but it's a good compressor and includes everything you need to fill an RV tire, or all 4 tires on your 4x4 if you use it in the sand. The Bon-Aire is going in the yard sale, this is going in the tool compartment on the RV.

Overall, I'm very pleased with my purchase and the quality of this unit. Since writing the above article, I've had a chance to use it to air up the tires in my Jeep after a sandy excursion in the Everglades and to add about 15 PSI to all 6 tires on an RV that had sat for several months. After the second task, the compressor was pretty warm, but it took it all in stride and did the job.
Eric - Big Pine Key, FL
2003 Holiday Rambler 29RBD/2006 Jeep Liberty CRD
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Old 05-09-2014, 09:20 PM   #2
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Join Date: Aug 2001
Location: North America somewhere
Posts: 28,532
Good 12V compressors. I bought a Harbor Freight knock-off 6 years ago and it's still working as new. It however, has something like a 40% duty-cycle. Viair has a 100% duty-cycle, and may be used with a 5G storage tank.
2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
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Old 05-10-2014, 10:40 PM   #3
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I have this compressor and have used it many times to air up my jeep tires. It is a good compressor. My only complaint is the cheap yellow coil air hose. It got a crimp in it and needs to be replaced.
2018 Ford F-150, 2019 Grand Design Reflection
From the Land of Enchantment, New Mexico
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