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Anybody who read my thread about the speed of the 400H and 400C compressors knows that I had a little torture testing that I've been wanting to do. Finally had some warmer weather today and I've completed the torture test.

Some back story, and why am I doing this? The 400H and 400C are the same compressor, other than the fact that the 400H has an integrated on off switch. These two compressors are very interesting for two reasons. First off they are among the fastest compressors that Viair offers, putting up to 2.56 CFM. The are also among the lease expensive compressors that Viair offers. Their size makes them a natural to install in the JK engine compartment. 

Viair Compressor Speed Comparison Data:

Viair 400c Compressor


For the price and size the 400C and 400H stand out as the speed leaders, in a big way.

The big question for these compressors is duty cylce. Rated at 33% duty cycle at 100 PSI, how would they do filling tires?

My first test was filling 8 tires, connected through an air manifold to 4 tires at a time. The first set of tires were 37's on 17" rims and they were followed by 35's on 15"rims. The fill time for all eight tires was 50 minutes. So with no more than a very short break the compressor did not overheat with a 50 minute run time. Of course, I wanted to know more so... I decided to torture this little compressor and here's what I did.

My goal was to see how long the compressor would run. These compressors are are equiped with thermo-protection and automatically shut down when they get too hot. I gathered up a 20 gallon air tank, 50 foot air hose, a high quality liquid filled Wika pressure gauge, infrared thermometer and a stop watch (later on, I had to find a 5 gallon water bucket - more on that later). I installed the pressure gauge on the air tank hooked one end of the air hose to the compressor and the other end to the air tank. I turned the compressor on and let it run, until the tank reached 30 PSI. I then opened the air tank drain valve and adjusted it, to where the pressure even. I didn't have a way to keep the pressure at a prefect 30 PSI, but it never dropped below 26 psi and never went above 34 PSI. Now these things get hot. REALLY HOT. After the compressor ran for a few minutes, I noticed that the air hose wasn't looking very good. The air coming out of the compressor was heating it and it looked like it was going to fail so I gathered up 5 gallon bucket of water. I emersed the quick connect fitting and a couple feet of hose to keep the air hose cool. This wouldn't effect the testing of the compressor in any way. Every ten minutes, from the 50 minute mark on, I checked the temp of the compressor head and outside cylindar wall. 

Here is the data:

jeep wrangler onboard air


The graph:

viair compressor comparison

Results and Conclusion:

After the compressor filled the 20 Gallon tank, it ran for 2 hours 32 minutes, then shut down. After about 20 minutes if fired back up again. 

On the tire fill testing the compressor filled four 37" tires from 9 PSI to 27 PSI in 16 minutes.

What have we learned from all this? First of all, we know that this is only a 33% duty cycle compressor. But two and a half hours at 30 PSI, that's friggin great. For filling tires, the 400C and 400H represent what I believe is by far the best value for compressor based onboard air systems.

5/16 update: Torture test part Two.

This one was a different and done for the guys who have been concerned about how the 400 series compressors will run after being in a hot engine compartment. For this test I really turned up the heat. Here's the test.

After a 2 hour drive from the desert.

I set out to repeat the following steps over and over again until the thermal protection kicked in on the compressor. Fill the 2 gallon tank to 145 PSI, drain the tank to zero and repeat. I figure this is the compressor running at an average of about 110 PSI, which should really kick it's butt. I defined success for this test if it would run continuously for 20 minutes in this manner. This given I was pleasantly surprised that it ran for a total of 54 minutes. Again, the 400 series compressor kicked ass. This is the same 400H that I've used for all of my testing.

As far as tires fills are concerned, I did gather one piece of data today. If I fill the tank to 145 PSI and turn the compressor off, the tank will fill one tire from 9 PSI to 18 PSI.

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