Honeywell HP970A, HP972B, HP970B Service Data
Honeywell
HP970A,
B and
HP972B
Pneumatic Humidistats
SERVICE DATA
HP970A,
B
HP972B
MB
Fig. 1. Typical
VALVE
SUPPLY
HP970A,
Two-Pipe Hookup.
6 or
HP972B
N.C.
C322.5
HP972B
Humidistat
The
HP97OA,
(Humidistats) are nylon element, proportional, two-pipe,
devices used to control humidity in HVAC systems.
HP970A
The
valve and damper actuators in air conditioning systems
requiring humidification and/or dehumidification.
The
HP972B
humidity as a function of outdoor air temperature, wide
throttling range, or replacement of existing one-pipe
humidistats” A special
necessary adapter fittings to convert older models or
competitors’ humidistats” Figure
13,
or
HP972B
HP972B
B and
HP972B
and B Pneumatic Humidistats control pneumatic
is used in systems requiring a reset of relative
Pneumatic Humidistats
model, HP972BI 013, has all the
1
shows a typical
two-pipe hookup. Figure 2 shows a typical
one-pipe hookup.
HP970A,
RESTRICTION
Fig. 2. Typical
(BLUE)
HP972B
HUMIDIFIER
VALVE
SUPPLY
Humidistat One-Pipe Hookup.
N.C.
~
C3226
SPECIFICATIONS
Action:
HP970A:
HP970B:
HP972B:
Means of Adjustment:
External knob with internally adjustable setpoint locking stops
Maximum Safe Pressure:
25 psi
Supply Air Pressure:
13 to 21 psi (90 to 145
18 psi (124
Branchline Pressure Indication:
Self-sealing gage tap under the cover
Direct Acting
Reverse Acting
Reverse Acting
for minimum and maximum settings
(172
kPa)
kPa)
kPa)
nominal
Copyright 0 1989 Honeywell Inc. 0 All Rights Reserved
75-7195
Ht=‘97OA,
B AND HP9728 PNEUMATIC HUMlDlSTATS
HP97CV4,
B: Adjustable TR factory set at 5% rh
3 to 15% rh Low Range
3 to 20% rh High Range
HP972B:
Adjustable TR factory set at 12% rh
7 to 35% rh Low Range
Ambient Operating: 45 to
Storage: -30 to l5OF (-35 to
125F
(7 to 516)
EC)
1972
HP970A
and B sense changes in ambient relative humidity.
The sensed change causes a proportional change in the
branchline pressure (BLP) and changes the control actuator
position by the same proportion. The
and the
HP9708
(RA) decreases the BLP when the relative
HP970A
(DA) increases
humidity increases.
The
WP972B
(RA) provides an inverse branch pressure
signal in relation to the sensed relative humidity. The wide
throttling range allows a reset of
reilative
humidity as a
function of the outdoor temperature, preventing condensation
during extreme winter conditions.
CLEA
If the Humidistat is in an area where it is exposed to
0
dust or dirt,
air hose or soft brush to remove accumulated dust or
dir-t.
if
the nylon sensing element becomes contaminated
0
with oil, grease, or dust, remove and clean it by
agitating it in an acetone solution. Dry the element at
room temperature.
the Humidistat.
The throttling range is factory set and should not
change under normal operating conditions. If a change in
relative humidity causes the system to hunt or the response is
too slow, reset the throttling range as follows:
If the system hunts or the controlled device cycles,
move the throttling range indicator down. If the
response is too slow, move the throttling range
up toward minimum.
@
Recalibrate the Humidistat each time the throttling
range is changed.
periodicaliy remove the cover and use an
meetly
Re~~sta~~
the efement and recalibrate
r~~~~re
any
ifldicator
The tools shown in Figure 3 and a sling psychrometer or
Digital Relative Humidity Pen
CCT915
are necessary to
calibrate the Humidistats.
PEN CCT915
ig. 3. Calibration Tools.
THROTTLING
INDICATOR
CALIBRATIO
LOCK SCREW
SE-i-POINT/
LOCKING STOPS
Fig. 4. Humidistat with t
djust
-----SETPOINT
ADJUSTMENT
NYLON
LEMENT
6301-3
75-7195
HP970A,
5 AND HP9725 PNEUMATIC
HUMID/STATS
SETPOINT LOCK ADJUSTMENT
Set the minimum and maximum setpoint as follows:
0
Loosen the setpoint lock screw (Fig. 4).
@
Move the setpoint locking stops to the desired position.
0
Tighten the setpoint lock screw.
@
Check the stop positioning by turning the setpoint
adjustment.
CALIBRATION CHECK
HP97OA
Measure the rh with an accurate rh measuring device.
Turn the
reads IO percent below the indicated rh and allow the
Humidistat to build up BLP.
Turn the
adjustment.
if the Humidistat bleeds off at 13 percent rh of the
indicated humidity, no further calibration is necessary. If
the Humidistat does not bleed off properly, proceed with
RECALIBRATION.
HP970B
Measure the rh with an accurate rh measuring device.
Turn the
reads 10 percent above the indicated rh and allow the
Humidistat to build up BLP.
Turn the
setpoint adjustment.
If the Humidistat bleeds off at &3 percent rh of the
indicated humidity, no further calibration is necessary. If
the Humidistat does not bleed off properly, proceed with
RECALIBRATION.
setpoint adjustment until the setpoint indicator
setpoint indicator up slowly using the setpoint
and
HP972B
setpoint adjustment until the setpoint indicator
setpoint indicator down slowly using the
RECALIBRATION
CAUTION
These Humidistats are sensitive devices and should
be handled with extreme care during calibration. Do
not breathe directly on the element when the cover
is off.
Ensure the system is stabilized and the main air is
maintained at normal pressure between 13 and 21
psi (90 and 145
(125
kPa).
Remove the Humidistat cover.
Install the Pressure Gage into the gage tap (Fig. 4)
using the Gage Adapter.
Measure the rh with an accurate rh measuring device.
Use the
indicator at the actual relative humidity.
Adjust the calibration screw (Fig. 4) until the Pressure
Gage reads 0 psi (0
Readjust the calibration screw slowly until the
Pressure Gage reads 8
Allow sufficient time for a complete response and
stabilization, then recheck pressure. The Humidistat
is now calibrated.
Remove the Pressure Gage and Gage Adapter.
NOTE:
Replace the Humidistat cover.
Set the Humidistat at the desired setting.
setpoint adjustment to set the setpoint
TROUBLESHOOTING
kPa).
Factory calibration is 18 psi
kPa).
If the gage tap fails to seal itself properly
after the Pressure Gage is removed, bleed
off a small amount of air and insert Gage
Tap Plug 14002172-001 into the gage tap.
+I
psi (55 f7
kPa).
Table 1 lists common Humidistat problems, their possible
causes, and solutions. For any problems not covered in Table
2, Troubleshooting Flowchart (Fig. 5).
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