We will make the basic assumption that the driver (motor, engine etc.) is operational and you have confirmed that it is the blower.

De-energize the system and lock out the power supply.
You must have access to the inlet or discharge of the unit so remove any filters, silencers or fittings that may interfere with your ability to take a look inside the unit. It is best if you have access to both inlet and discharge.
Remove any belt or coupling guard that may prohibit you from turning the shaft of the unit.
Inspect inside the unit and determine if there is any foreign material inside the unit (i.e.. plastic, cement, flyash, debris, rust etc..)
- If you do find an obstruction, remove it as best you can. Sometimes this may be next to impossible if the material has formed a hard coating on the internal components…but give it a try.
Rotate the shaft back and forth to determine if there is any motion. If you can partially rotate the unit, rotate the shaft back and forth to see if you can achieve a full rotation. DO NOT PUT A PIPE WRENCH ON THE SHAFT!! The lever arm available from a pipe wrench with strong operator could be enough to bend the shaft. This could be very costly to repair. We sometimes council people to use a pipe wrench on a sheave with some rags placed between the pipe wrench jaws and the sheave, but this must be done with great caution. You may also consider using a strap wrench.
If you can’t break it free or you can’t get a full rotation, you’ll probably want to remove the unit from the system and take it back to the shop for further investigation. If you have debris or material in the unit, it may need to be torn down and the effected components will need to be either solvent cleaned or sand (bead) blasted.
If the unit does not have debris in it and just appears to be rusty, there is hope! We use a product called PB Blaster (officially known as PB Penetrating Catalyst) which is a very effective penetrating oil. PB Blaster is typically available at your local auto parts store. Spray a liberal amount over the internal surfaces of the machine (headplates and impellers) and allow it to sit for a few minutes to a few hours based on how much rust you have. After allowing PB Blaster to work for a while, go back to step 5 and begin rotating the unit back and forth. Our preferred method on ROOTS units that utilize a locknut on the timing gears (Universal RAI®, ROOTS™ RAM™, ROOTS™ RAM™ WHISPAIR™, ROOTS-FLO® ) is to drain the oil out of the gearbox housing and remove the gearbox housing cover. We then use a socket and (most likely a 3/4″ or 1″ drive) ratchet on the drive rotor timing gear nut to rock the unit back and forth. Apply the greatest force in a clockwise direction. With a little to a lot of effort, the unit will usually free up. You must be carefull not to loosen the lock nut when you use this procedure. You must then continue to rotate the unit until it turns freely.
Put the gearbox cover back on, fill the unit with the proper type and amount of oil per the owners manual and you should be ready to reassemble your drive (v-belts or coupling). Put your piping back in place and you should be ready to energize your unit. We suggest that you “bump” the unit for a couple of seconds the first time you energize it and listen for knocking or other problems. If all appears well, go ahead and energize the unit and operate at minimum load for five minutes to make sure that it turns and performs properly. Assuming that everything “sounded” right (no knocking or dragging), you should be ready to put the unit back under load.

Sometimes units are too rusty to be broken free with this method and they must be torn down, cleaned (usually via sand blasting) and reassembled. If you have to go through the process of tearing down the unit, we recommend that all bearings, seals and gaskets be replaced.