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Description
Correct pressure switch operation is integral
to the safety of a furnace environment.
The DDSM1 teams with your accurate
manometer to accurately test pressure switches.
The DDSM1 creates a negative pressure
(vacuum) and detects a closed switch. Your
manometer tells you what the pressure is when
the switch activates.
General Setup
Fieldpiece
Draft Simulator
OPERATOR'S
MANUAL
Model
DDSM1
Controls and Ports
A
Pressure dial (Clockwise increases vacuum.)
B
Ports to negative side of switch and your
manometer. (Close one OFF if only using one.)
C
Power button:
High Speed>OFF>Low Speed>OFF
(some models use a rocker switch: I=Low, II=High)
D
Closed-switch LED indicator.
E
Jacks to switch terminals.
Functions
Test a Pressure Switch
WARNING: Turn off power to furnace prior to
testing to avoid low voltage shorting.
1. Connect leads to normally open and com-
mon terminals of the pressure switch. It
does not matter which lead goes to which
terminal.
2. Connect both hoses to the ports on the top of
DRAFT SIMULATOR. Connect one hose to the
negative side of the pressure switch and the
other to your manometer. It does not matter
which hose is connected to the manometer
and the pressure switch.
3. IMPORTANT: Before starting the DRAFT
SIMULATOR, ensure the pressure dial
is completely open by turning the dial
counter-clockwise as far as it will go.
Turn on and "zero" your manometer.
There are two major speeds to accommo-
date different pressure switch ratings – a
low speed and a high speed. The speeds are
accessed alternately by pressing the power
button multiple times as shown below:
OFF – HIGH – OFF – LOW
4. Turn on the DRAFT SIMULATOR. It is a good
idea to start the DRAFT SIMULATOR in high
speed to warm-up the motor for 10 seconds.
5. Set the DRAFT SIMULATOR to the major speed
needed for testing the pressure switch. Use
low speed to test pressure switches rated
between -0.10 inches of water column and
-1.50inWC. Use high speed to test pressure
switches rated 1.50inWC to 12.00inWC.
6. Slowly close the pressure dial by turning it
clockwise (increasing the vacuum) paying
attention to the indicator light on the front
of the DRAFT SIMULATOR and the readings
on the manometer.
7. The light will come on when the pressure
switch closes. Note the reading on the ma-
nometer. Manufacturers have a rating when
the pressure switch should close. A good
pressure switch will close within 10% of the
manufacturer’s rating.
8. To see when the switch opens, slowly open
the pressure dial by turning it CCW. When the
light of the DRAFT SIMULATOR goes off, note
the reading of the manometer. The reading
should be within 10% of the rating on the
pressure switch.
NOTE: Most pressure switches have bleed ports
in them to drain moisture. This also helps to
avoid excess pressure created by the draft
inducer and controls the amount of pressure
required to close the switch. The amount
of pressure required to close and open the
switch should still be within 10% of the
manufacturer’s rating. The pressure required
to close the switch should never exceed the
amount of pressure created by the draft
inducer.
NOTE: Many pressure switches have an orifice
in the port. This increases the time it takes to
close or open the pressure switch. This does
not mean it takes more or less pressure to
close the pressure switch. The pressure switch
should still close and open within 10% of the
rating.
NOTE: Dual-port manometers are usually setup
to use the positive port (P1) with the DRAFT
SIMULATOR.
Indications of a Pressure Switch out of
calibration, weak or bad diaphragm or a bad
micro switch in the pressure switch:
o The pressure switch will not close or open
within 10% of its rating.
o The indicator light on the DRAFT SIMULATOR
“flickers” on and off rapidly.
o Manometer readings fluctuate when no ad-
justments are made to the pressure dial on
the DRAFT SIMULATOR.
o The measured readings are greatly affected
when the hose to the pressure switch is
pinched.
Pinch Test - Proving the
Diaphragm
o Test the pressure switch and note the findings
using the DRAFT SIMULATOR.
o Pinch the hose closed to the pressure switch
while performing the test.
o If the pressures differ more than 20% from
the original findings, you may have a bad,
cracked, or leaking diaphragm in the pressure
switch. If the pressure doesn’t differ you may
have a blocked bleed port.
Prove or Rule Out the Inducer
o If the pressure created by the inducer mea-
sures more than enough to close the pressure
switch but the DRAFT SIMULATOR proves
the pressure switch to be good, the inducer
may not be providing enough cfm (cubic feet
per minute) to close the switch. The inducer
should be replaced.
A
B
C
E
E
D
inWC
One hose goes to manometer.
One hose goes to
negative side of switch.
Leads go to switch terminals.
(normally open and common)
99 Washington Street
Melrose, MA 02176
Phone
781-665-
1400
Toll Free 1-800-517-8431
Visit us at www.T
estEquipmentDepot.com
