Hi Jeff,
I can’t believe that the “repairman” said it was working because it was turning. Many problems could let it run but not move enough air. It sounds like the bigger problem is with the “repairman.” You need an HVAC technician. It could be a nasty and smelly job. Not all HVAC companies take them.
Assuming nothing on the system was changed before the problem started, here are some possibilities, that let could keep running but not working.
Off value capacitor
Low or high voltage
Bad belt
Bad bearings or bushings
Bad pole
Phase imbalance or reversal
Bad motor protector
Bad or out of adjustment pulley
Etc
If the ventilation system had been worked on before the problem;
Fan blade damaged, wrong size, reversed or wrong rotation
New motor too small or large (yeap, too large)
Housing reassembled improperly
Wrong capacitor
Controls improperly wired
Etc
The problem could be with the building or the make up air as others have said.
The majority of the problems I have seen require a simple inexpensive belt change. This is so common that I would buy an extra belt and leave it in the unit for the next time. The belt should be adjusted so that there is 1 inch of play in the belt.
If you try to fix it, make sure the power is turned off. Not just that the fan turned off. Breaking 1 line is enough to turn it off but you could still loose a finger. All the lines must be broken.
I would not recommend replacing the hood system only because of this problem. I can’t imagine a component failure that could make that worthwhile. It’s like replacing a car because of a bad radiator. But if you want a new car, go for it.
If you want a new hood system, I’d go for the high tech ones. The variable speed intelligent ones. A sensor determines when and how much ventilation is needed. The energy savings payback is suppose to be about 2 years. Make sure you get a technical manual for it, not just an owner’s manual. Then don’t let it out of your site. Techs like manuals.
I would recommend that you make sure the refrigeration condensers are clean. The high temps are tough on the ones with the condenser on top. When they over heat, the oil breaks down and eventually the compressors fail.
Hope this helped,
Kenneth
www.RefrigerationSecrets.com www.refrigeration-repair-tips.com