31
TROUBLESHOOTING
General
If system design parameters have been met, such as ductwork
size, airflow rate, etc., improper operation can often be traced
to leaks or obstructions. The following paragraphs describe
the general procedure for checking for leaks or obstructions.
Before performing any check, be sure that plenum pressure is
a minimum of 0.75-in. wg and that supply-air temperature is
50°F to 60°F and room temperature is 70°F to 80°F.
Checking for Obstruction
If there is an obstruction, the unit fails to respond either par-
tially or completely to thermostat changes, but does not show
any indication of a control circuit leak.
Check the bellows pressure at each inlet and outlet. Pressure
at every point in bellows circuit should be the same. The ob-
struction may be kinked control tube.
Checking for Leaks
The center diffuser of these units is not removable. Gain ac-
cess to unit controls by raising ceiling tile.
1. Master units can be identified by means of thermostat
lever extending below diffuser. See Fig 42.
2. Disconnect slave from master by disconnecting the inter-
unit tubing. Mark tubes clearly to assure proper reassem-
bly. Cap ports on master unit to isolate it. Then move
thermostat lever to full red (warm) setting and observe
whether unit shuts off.
3. Check for cracked plastic parts, loose or cracked tubing
or a loose filter. Remove filter and check that filter open-
ing is not obstructed; then replace filter.
4. Remove thermostat/volume controller assembly. Attach
Magnehelic gage to bellows connection with rubber
tube. (See Fig. 43.) Blow into tube until unit shuts off.
Hold tube so that no air escapes. Dial on Magnehelic
gage dropping or the opening of the diffuser slot dis-
charging air will indicate a bellows leak. If after approxi-
mately 30 seconds no leak is detected, the bellows are
satisfactory.
5. If unit appears satisfactory, replace the thermostat/vol-
ume controller assembly and connect it to the unit. See
Control Installation section page 23.
6. Test whether master unit (isolated, without slave units)
will control. If no control, check duct pressure as
described in the section below.
7. If master unit controls properly, add one slave unit, mak-
ing sure air is flowing from both sides of diffuser. If both
units control, add another slave; and so on down the line.
8. If control is lost by adding a new slave, check for loose,
cracked or disconnected tubing. Isolate that slave and
cap all bellows ports. Attach a Magnehelic gage to one
port and blow into it. The Magnehelic gage will be
needed to detect a leaking bellows.
9. If possible, check bellows pressure at each unit by attach-
ing Magnehelic gage tubing to a bellows port for 2 to 3
minutes after stabilization takes place. Record values.
10. Take duct readings with all units connected and operat-
ing. Reference the Check Duct Pressure section. To
record data on slave unit, remove high-pressure port plug
(Fig. 36) and insert Magnehelic gage tube into opening.
Replace plug after test.
11. If units are still not controlling, check inter-unit control
tubing for possible holes, breaks or pinching between the
2 units where control apparently was lost.
To Check Duct Pressure
To check duct pressure on master unit, remove the volume
controller from the filter and connect a Magnehelic gage tube
to the filter high-pressure port (shown on Fig. 33). After
checking, replace volume controller. Check the slave unit by
removing the plug from the high-pressure port on the slave
unit (shown on Fig. 30) and connecting the Magnehelic gage
tube. Replace plug after checking.
See Table 6 for minimum required duct pressures at various
air quantities.
Fig. 43 — Checking Unit Bellows for Leaks
0
1
2
3
4
5
6
MA
GN
EH
ELI
C
OF
W
AT
E R
®
BLOW INTO
THIS TUBE,
CLOSE OFF
METAL "T"
DIFFUSER
BELLOWS
CONNECTION
