DIY Network

HVAC: Fan Maintenance From "Trade School" episode DTRS-212

(Continued from page 1)

Figure A

On this day, Patrick's first order of business is to inspect and optimize one of the powerful supply fans used in this system (figure A). While the fan in a home unit primarily serves to only blow air in or out of the home, this large axial fan also works to control the volume and pressure of air throughout the entire building. Patrick relies on the expertise of journeyman Terry Monks and a workflow checklist to do the job correctly.

advertisement

	Figure B
	Figure C
	Figure D
	Figure E
	Figure F
	Figure G
	Figure H

Basic Tools:

open and adjustable wrenches
allen wrenches
dial indicator
cleaning solvent
heavy duty paper towels
scraper
grease pump

After disconnecting the power source for safety, Patrick checks the pitch of the fan blades. The fan is controlled by a computer system that adjusts the blade angle to regulate the pressure inside the building. Patrick traces the arc angle at the end of one blade by scraping into the surrounding dust (figure B). As he rotates the fan, he verifies that each subsequent blade lines up exactly to the trace mark.

Next, Patrick disconnects the diagonal pitch bar at both ends using wrenches. The pitch bar is the outer most component of the pitch assembly, which works to synchronize the opening and closing of the blades. Patrick also disconnects the grease line, through which oil regularly pumps to the mechanism.

Patrick marks the position of the dust cover with a marker for reference for later reassembly. He then unscrews the bolts and removes the dust cover.

Using an allen wrench, Patrick removes the nose of the pitch mechanism to expose the bearing assembly (figure C). He notes that the bearing seems a little dry, so while Terry rotates the fan, he pumps thick grease through a stem in the pitch disk. When enough grease has been pumped, he reconnects the nose.

Then, after marking the pitch disk for reassembly, he removes the entire pitch mechanism (figure D). To free the mechanism he must release each crank arm through a groove in the pitch disk. The crank arms serve to turn each blade in unison.

With the pitch mechanism removed, the crankshaft is now visible. Patrick takes this time to check the fan blades and rollers on the end of each crank arm to make sure they rotate freely (figure E). Then he reconnects the pitch arm to mount a dial indicator. After preloading the dial indicator, he checks for any variance in the rotation of the crankshaft (figure F).

After finding no problems with any of these components, he cleans the crankshaft using a cleaning solvent and paper towel. Then, he lubricates the crankshaft with heavy grease.

Patrick removes the pitch bar and reassembles the unit working in reverse order. Then he scrapes grime build-up off the leading edges of the fan blades with a scraper. He reattaches the grease line, pitch bar and safety screen (figure G).

For the final inspection of the axial fan, Patrick climbs on top of the unit to access the motor wiring case. After removing the cover, Patrick inspects each wire terminal to make sure nothing has become dislodged due to the constant vibration caused by the fan. After finding the wiring to be in working order, he uses a grease pump to lubricate the hidden motor bearings.

To complete this stage of the project, Patrick reconnects the electricity and turns the fan on to verify his work (figure H).

In the next segment, we follow Patrick as he performs an annual check on the building's centrifugal chiller.

1 | 2

RESOURCES :

Chiller System Services Inc.
1510 Swadley St.
Lakewood, CO 80215
Telephone: 1-303-275-6250