Jeff wrote in an said “The compressor appears to compress the air but there no air at the hose.This is a Craftsman model 921.166460 with a 5 gallon tank on a nice little cart. I have replaced the gaskets, sprayed the unit with soapy water and verified that there are no leaks. I checked before and after the check valve and have compressed air. Both gauges do not show any pressure and there is none when I connect the hose. — Where is all that the compressed air going to? Again, the soap test show no leaks anywhere.


Meanwhile, I recently purchased a similar small Campbell Hausfeld at a yard sale with an 8 gallon tank.. There was no air at the hose port (no quick connection or hose either, but I replaced those). I assumed it was the gaskets and replaced them but still had no air at the hose — but there was air blowing out of the check valve and a “black worm” hanging out of the valve, as well. I replaced the “o” ring (the black worm) in the check valve and the unit is now running like a top.

What have I overlooked in the Craftsman?


Jeff, a photo of the Craftsman 921.166460 compressor would help all of figure out what’s going on. I couldn’t find a photo of this one anywhere.

Anyway, let’s work on this.  You say “Both gauges do not show any pressure”. That strongly suggests there’s no air in the tank. That is, unless the feed tube that leads to the tank gauge, the regulator and regulator gauge and the coupler into which you push the air hose connect is blocked, and that I’ve never heard of happening.

Or, the the gauges are  broken and there is air in the tank. Let’s check.

If the gauges work, and there is no blockage, after the compressor has been running for a few minutes, crack open the tank drain. What happens? Does any air bleed out? If so, let it all bleed out for now as there may have been residual air in there from before the failure. Close the drain, run the compressor for 3-4 minutes, and open the drain again. Any air bleeding out?

If not, then that compressor cannot be building pressure, else it would show on the tank gauge.

Does this model have lubrication? Is there an oil fill port under the dipstick? While the compressor is running, is air blowing out the dipstick cover? Enough for you to feel? If so, this compressor may have a significant piston seal leak, and all the air that’s being built is blowing out the oil fill vent hole and not going into the tank.


Thanks, Bill — but what’s the fix, says Jeff?

I have dis-assembled and re-assemble portions of tracking the air.. It is blowing compressed out of the head cylinder and beyond the check valve and beyond the safety valve but, apparently, its is losing it somewhere between there and the gauges and tank.

The compressor is lubricated by oil but it has no dipstick. Rather, it has a sort of 2 inch black “top hat” cap on top and a visible glass port on the side where you are to keep the oil just above its red dot. It is not blowing air out the “top hat”.

I will admit that I did, at one point, over-filed it with oil but now we are just above the red dot. If you overfill it (and I did), it will blow oil out of the “top hat”.

Whaddya think the problem/fix is?


Just FYI Jeff, filling the oil level to the middle or the center of the dot in the sight glass shows the correct “full” reading for that compressor.

If both gauges are not showing pressure, and assuming they work, then the compressor is NOT building pressure, simply moving a small amount air that may feel like pressure buildup, but isn’t really.

When you say “It is blowing compressed out of the head cylinder” can you explain further how you know that? If it is true, it suggests that there is a gasket failure, and the pressure that’s being built by the cycling of the piston is cycling from a slightly higher pressure level to lower through a gasket. That’s going to require a gasket replacements if that’s happening, and that means opening up the pump.

If no air is blowing oil out of the “top hat” that suggests that the piston seal is OK. This is probably a splash lubed compressor and I guess oil could splash up the fill tube and out yet there should be virtually no air in the sump to blow it out.

Once again, the absence of any photo of the compressor, compressor pump, and areas you are referring to is making this quite difficult to resolve.

Once again, if the pump is cycling with the motor running, and both gauges are not registering pressure build up in the tank and both gauges are fine,  then the pump is not compressing air.

The logical reasons are damaged seals in the cylinder, the valves are broken or jammed, or any pump head gaskets have breached, that pretty much sums up what should have to be at fault for no air build.

Open the pump and find the fault in those and fix it and if the motor runs properly the compressor will then generate pressure. Good luck.


Jeff, can you double-check that model number? I’m not finding it.
And if you open the tank drain valve, do you get air for a few seconds? Doug from


Thanks, Doug

You are right the correct model number is 921.166360. (not 921.166460).

As you suggested, I opened the tank’s drain valve; there is no air in the tank.

As I said, it appears there is compressed air coming out of the cylinder head, out of the check valve, through the pressure tube assembly — but:

there is no air at the safety valve and beyond OR in the tank. All the gauges are not moving at all. I can not figure out where all the air is going.

I am open to all suggestions.— thanks again.


Doug says,

I presume you’ve found the parts diagram and list for this. I’d suspect either of these, from what you’ve said:


00049 PRESSURE RELIEF TUBE ASSY. 16636 $3.18

Additionally, if both of those are unbroken and connected properly, that would leave the unloader valve in the pressure switch connected by 00049. It’s $44, but you can probably get something off the shelf for much less, if that’s the trouble.

Good luck.