| A few years ago I purchased a VIAIR 78P 12V compressor to replace my depleted OEM air canister. The compressor worked fine for topping off my tire pressure the last 2 years, but it failed to inflate the spare when I recently needed it. For reference my spare is a yellow-painted model from 1996. The spare was mounted and the compressor hooked up but after several minutes of no change in the pressure I found the air was leaking out between the tire edge and the wheel rim. I tried pulling/pushing the tire a bit but it didn't affect the leak. I took the spare to a nearby repair shop, with the wheel laid flat on the ground they tried with their normal air hose and the tire pumped right up and held the pressure fine for weeks. When I eventually removed the spare I thought I'd try the compressor again as I realized I didn't originally have the spare oriented with the valve at the 6 o'clock position called out in the owner's manual. I fully deflated it, leaned it against my rear wheel with the valve correctly oriented and unfortunately got the same result. Rotating the wheel didn't seem to affect the leak. I also tried laying it flat on the ground but that didn't work either. My best guess is that the CFM of the compressor is too low to both leak some air and inflate/push the tire out against the rim to make an air-tight seal. The spec for the VIAIR 78P is 1.06 CFM. I called VIAIR and spoke to one of their techs, and while he tried to help he never seemed to really understand the problem. One thing he mentioned when discussing the higher-CFM models they offer, was that my model may not be operating at full performance if the Z's 12V power port isn't providing the full 15 Amps of power the compressor is designed for. Has anyone successfully used a 12V compressor to inflate the space saver spare? If so can you share the make/model or the specs? Is my problem a CFM issue? Is the Z providing 15 Amps of accessory power? Do I have to go with a battery clamp model? Thanks in advance. Sorry for the long post.
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