Pressure Switches - International comfort products N9MP1 Service Manual

Service Manual
N9MP1 & N9MP2 MAIN LIMIT SWITCH
MODEL PART #
050B12C 34335002
075B12C 34335001
080F16C 1320361
100F14C 1320361
100J20C 1320367
125J20C 1008445
ROLL OUT LIMIT SWITCH
MODEL PART #
ALL 1013102
*9MPD MAIN LIMIT SWITCH
MODEL PART #
050B12C 1320366
075F12C 34335002
080J16C 1320367
100J14C 1320367
100J20C 1320367
125L20C 1008445
ROLL OUT LIMIT SWITCH
MODEL PART #
ALL 1013102
To verify this, the cut−out (opening) point of the switch
should be checked (using a thermocouple type thermome-
ter connected to the face of the switch) as follows:
1. Operate furnace for several minutes.
2. Block return air grille(s) to furnace.
3. Observe temperature at which switch opens (burner
operation ceases).
4. Remove blockage from return grille(s).
5. Observe temperature at which switch closes (burner
operation resumes).
6. Compare readings with the limit setting listed in the
appropriate chart for the model you are servicing.
If switch is opening within the specified range, then it is sim-
ply doing its job, and the cause of the over−temperature
must be determined and corrected.
If, however, the switch is found to be opening prematurely,
then it should be replaced. When replacing ANY limit
Transition Pressure Switch
An air proving switch (pressure) switch is used on all mod-
els to insure that a draft has been established through the
heat exchanger before allowing burner operation.
16
OPEN CLOSE
240° F 220° F
210° F 190° F
230° F 210° F
230° F 210° F
220° F 200° F
190° F 170° F
OPEN CLOSE
300° F MANUAL
OPEN CLOSE
260° F 240° F
240° F 220° F
220° F 200° F
220° F 200° F
220° F 200° F
190° F 170° F
OPEN CLOSE
300° F MANUAL

PRESSURE SWITCHES

Single Stage Multi Position Furnace
switch, use ONLY a switch of EXACTLY the same tempera-
ture setting. Use of a different temperature limit switch can
create a dangerous situation. Some of the main limit
switches used in this series are SIMILAR IN AP-
PEARANCE. DIFFERENT TEMPERATURE SETTINGS,
HOWEVER, ARE USED for different models. Be certain
you have the correct control for the model you are servicing.
ROLL OUT LIMIT
A "Normally Closed" switch (wired in series with the Main
Limit switch) mounted on both sides of the burner box.
This switch is a manual reset type. When replacing this
switch, be absolutely certain the correct one is used.
Figure 12
Typical Roll Out Limit Switch
CAUTION
!
NEVER use an automatic reset roll out switch to
replace a manual reset type roll out switch.
Doing so may cause potentially unsafe and/or
intermittent operation.
The roll out switch monitors the temperature inside the
burner box, and interrupts furnace (burner) operation when
its temperature indicates flame roll out has occurred.
Once the roll out switch has opened, burner operation will
be prevented until the roll out switch is "Manually Reset" by
pressing the red button located on the switch. While the roll
out switch is open, the combustion blower and circulating
blower will be energized continuously.
If the roll out switch has opened, the cause must be deter-
mined. Some possible reasons for flame roll out include a
restricted primary or secondary heat exchanger or over
fired furnace.
All models use a single tap (port) type switch. This switch
senses the negative pressure created by (at) the combus-
tion blower.
Under normal operating conditions, sufficient pressure is
developed by the exhaust (combustion) blower to close the
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