Pool Spa Blower Problem

My pool was installed about 13 years ago and I have been very happy with it. I have two pumps, one for the pool/spa circulation and one for the spa jets. I also have an air blower that pushes air into the spa via about twenty small holes in the bottom of the spa. The spa jet pump motor burned out about two years ago and I just got around to having it fixed yesterday. They installed an intelligent circulation pump and a fixed speed replacement pump for the spa jets. They also installed a new intelligent controller with a remote control. Everything works perfectly except when the air blower comes on no bubbles come out of the holes in the bottom of the spa. This used to work very well with strong bubbles coming out. They did not replace the air blower and the installers did not feel responsible for this problem (and I agree). I turned on the air blower and checked below the check valve and strong air is coming out. The air blower will run for about three minutes and then shut off (probably due to overheating). It will start again after cooling down. I drained the spa down to pool water level and used a metal coat hanger to check the holes in the bottom of the spa. None seemed to be blocked. I hoped the lower water level in the spa would allow the air blower to push through, but no such luck. There must be some sort of blockage somewhere but it's a completely sealed system and there is no way a small animal could have gotten into it. I don't know what to try next and any advice is very welcome. Thanks.
 
With the spa empty, you could try a strong wet vac on the air pipe (remove blower) to see if you can suck anything back out.

Was the air pipe left open while the spa blower was inoperative?
 
I put together an adapter to connect my water hose to the pvc air pipe and run water through the system. The water initially pushed air out of the holes in the bottom of the spa and after the air was out of the system just water came out of the holes. So, I guess I don't have a blockage. The blower still comes on and I can feel air coming out of it when I lift it off of the pvc pipe base. I guess it is no longer powerful enough to push through the system, although if it is putting out air it seems some would come through to the spa even if it was weak. The air pipe system has never been exposed so there is no way anything could get into the closed system. The next step is to replace the blower and see what happens. Thanks for the suggestions.
 
The blower must be powerful enough to overcome the weight of the water. So if the water is 3' deep, the blower must produce a little over 1 psi to get the water out of the way. But blowers don't become weaker unless the fan blade is broken but you should be able to see that. Is there an air bypass that is allowing air to escape. Another possibility is something got in the air pipe that is adding restriction but not preventing all the air flow.
 
An induction motor on a fan or pump will not run very long if wired incorrectly. It will either trip the breaker, trip the thermal limiter switch or burn up the motor. All of which are pretty apparent.
 
I haven't replace the blower yet, so it's still the original and it seems to blow pretty strongly. I have decided I must have a blockage. I was able to force water through the system but I can tell there is a lot of resistance. My next step is to cut the pvc pipe at the Hartford loop and narrow down where the obstruction might be located. If I get air from the blower to the Hartford loop then I know the blockage it between there and the spa.
 
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