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G25MV
Corp. 9505–L2
Service Literature
G25MV SERIES UNITS
G25MV series units are mid–efficiency gas furnaces
manufactured with tubular steel heat exchangers
formed of aluminized steel. G25MV units are available
in heating capacities of 60,000 to 120,000 Btuh (17.6 to
35.2 kW) and cooling applications from 1.5 through 5
tons (3.5 through 17.6 kW). Refer to Engineering Hand-
book for proper sizing.
Units are factory equipped for use with natural gas. All
G25MV units use a hot surface ignition system. The
G25MV units meet the California Nitrogen Oxides (NO
)
x
Standards and California Seasonal Efficiency require-
ments. All units use a two stage gas valve along with a
two stage induced draft blower assembly. The gas valve
is redundant to assure safety shut–off as required by
A.G.A. or C.G.A.
All G25MV units are equipped with an electronic vari-
able speed (VSM) fan motor. The VSM motor maintains
a specified air volume throughout the entire external
static range.
Units may be installed in upflow, downflow or horizon-
tal position. The heat exchanger is designed for upright
or horizontal use only. When the unit is installed in the
downflow position, the heat exchanger is field re-
moved and reinstalled so it is upright when the cabinet
is inverted. No field conversion is required when the
unit is installed in the horizontal position.
The heat exchanger, burners and manifold assembly
can easily be removed for inspection and service by sim-
ply disconnecting gas, unplugging wiring harnesses
and removing four screws holding the heat exchanger in
place. The heat exchanger slides out of the cabinet.
Information contained in this manual is intended for use
by Lennox service technicians only. All specifications
G25MV
are subject to change. Procedures outlined in this manu-
al are presented as a recommendation only and do not
supersede or replace local or state codes.
1995 Lennox Industries Inc.
Page 1
LITHO U.S.A.
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Summary of Contents for Lennox G25MV Series
- Page 1 G25MV Corp. 9505–L2 Service Literature G25MV SERIES UNITS G25MV series units are mid–efficiency gas furnaces manufactured with tubular steel heat exchangers formed of aluminized steel. G25MV units are available in heating capacities of 60,000 to 120,000 Btuh (17.6 to 35.2 kW) and cooling applications from 1.5 through 5 tons (3.5 through 17.6 kW).
- Page 2 SPECIFICATIONS Model No. G25MV3-60 G25MV3-75 G25MV5-100 G25MV5-120 Input Btuh (kW) high fire 60,000 17.6) 75,000 (22.0) 100,000 (29.3) 120,000 (35.2) Output Btuh (kW) high fire 48,000 (14.1) 60,000 (17.6) 80,000 (23.4) 96,000 (28.1) DA.F.U.E. 80.0% 80.0% 80.0% 80.0% Input Btuh (kW) low fire 40,800 (12.0) 51,000 (15.0) 68,000 (20.0)
- Page 3 VENT ADAPTER CABINET TOP G25MV PARTS IDENTIFICATION HEAT EXCHANGER ASSEMBLY FLUE BOX FLUE THERMOSTAT COMBUSTION AIR PRESSURE BLOWER SWITCHES G25MV CABINET PRIMARY LIMIT FRONT LOUVERED PANEL TURBULATOR BURNER BURNER ASSEMBLY CONTROL BOARD SECONDARY VSP2 LIMITS BOARD CABINET BOTTOM TRANSFORMER VARIABLE SPEED BLOWER BLOWER MOTOR ASSEMBLY...
- Page 4 I–UNIT COMPONENTS (Figure 1) Pre-Purge On a call for heat, the combustion air blower begins G25MV unit components are shown in figure 1. The operating. If the combustion air prove switch closes, blower controls, gas valve and burners can be accessed the combustion air blower continues to operate for by removing the front access panel.
- Page 5 G25MV BURNER CONTROL (A3) PLUG P20 See Table 2 for Terminal Functions LINE VOLTAGE TERMINAL CONNECTIONS See Table 3 for Terminal Functions 24VAC VOLT TERMINAL CONNECTIONS THERMOSTAT DIAGNOSTIC CONNECTIONS (TB1) FIGURE 3 Diagnostic LED DANGER The burner control is equipped with a diagnostic LED used for troubleshooting the unit and the control.
- Page 6 TABLE 3 4–VSP2 Blower Control Board (A24) BURNER CONTROL A3 TERMINAL DESIGNATIONS G25MV units are equipped with a variable speed motor Terminal Type Function that is capable of maintaining a specified CFM through- 24VAC OUT 1/4” Spade 24VAC Out To VSP2 out the external static range.
- Page 7 Diagnostic LED Lights VSP2 BLOWER CONTROL BOARD (A24) a-DS3 ON/OFF" ON/OFF–DS3 indicates there is a demand for the blower motor to run. When the ON/OFF LED–DS3 is lit, a demand HIGH ADJUST HEAT is being sent to the motor. In heating mode only, there is a TEST –...
- Page 8 To change jumper positions, gently pull the jumper off the The HEAT jumper selections are activated with a call for pins and place it on the desired set of pins. The following second-stage heating (W2). section outlines the different jumper selections available IMPORTANT and conditions associated with each one.
- Page 9 TABLE 5 VSP2–1 OPERATION HEATING MODE COOLING MODE UNITS WITH UNITS WITH UNITS WITH SINGLE– UNITS WITH TWO–SPEED SINGLE–STAGE HEATING TWO–STAGE HEATING SPEED COMPRESSOR COMPRESSOR NON–ZONED NON–ZONED NON–ZONED NON–ZONED APPLICATIONS APPLICATIONS APPLICATIONS APPLICATIONS When a single-stage thermostat is Using a two-stage thermostat with The terminals “DS”...
- Page 10 G25MV series blower motor ratings are listed in table 6. All G25MV blower motors use single phase power. D.C. motors. Internal components are shown in figure 10. An external run capacitor is not used. The motor uses The stator windings are split into three poles which are permanently lubricated ball-type bearings.
- Page 11 The DC filter capacitors inside the controller are con- Motor Start-Up nected electrically to the speed tap wires. The capacitors When B3 begins start-up, the motor gently vibrates back take approximately 5 minutes to discharge when the and forth for a moment. This is normal. During this time disconnect is opened.
- Page 12 External Operation (Speed Tap Priority) 2–Choke Coil (L13) A choke coil is used on all G25MV units. The choke is Figure 12 shows the two quick-connect jacks (J48 and located on the blower housing and is used to block radio J49) which connect the motor to the G25MV.
- Page 13 3–Secondary Limit Switches [(1)S21 and (2)S21] SECONDARY LIMIT SWITCHES FOR G25MV SERIES UNITS The secondary limit switches [(1)S21 and (2)S21] on (1)S21 G25MV units are located in the blower compartment on the back side of the blower housing (see figure 8). When excess heat is sensed in the blower compartment, the limit will open.
- Page 14 G25MV BURNER ASSEMBLY (shown in upflow position) ROLLOUT SWITCHES (S47) BURNER BOX VEST PANEL UPPER BURNER MOUNTING RAIL BURNER FLAME SENSOR LOWER HEAT EXCHANGER BURNER MOUNTING PRIMARY LIMIT (S10) RAIL ORIFICE HOT SURFACE IGNITOR Back Left GAS VALVE Right (GV1) Front BURNER BOX MANIFOLD...
- Page 15 NOTE–Do not attempt to regulate low fire manifold pressure. ROLLOUT SWITCH (S47) WHITE RODGERS 36E SERIES GAS VALVE MANUAL RESET BUTTON FIGURE 17 HIGH FIRE MANIFOLD PRESSURE 4–Primary Limit Control (S10) ADJUSTMENT ON SIDE The primary limit (S10) on G25MV units is located in the middle of the heating vestibule panel (see figure 16).
- Page 16 (101.94Pa + 12.43Pa) (49.73Pa + 7.46Pa) NOTE: All measurements are negative. G25MV series units are equipped with two combustion air II–PLACEMENT AND INSTALLATION prove switches located on the vestibule panel. The switches “T” together and are connected to the combus-...
- Page 17 Use of a C–Safety or Emergency Shutdown specialty Gas Leak Detector is strongly recommended. It is available through Lennox under part number Turn off unit power. Close manual and main gas valves. 31B2001. See Corp. 8411–L10, for further details.
- Page 18 NOTE– To obtain accurate reading, shut off all other VSM CHECK–OUT gas appliances connected to meter. A kit is available from the Lennox parts center to use in testing G–High Altitude Derate the variable speed motor. The kit 70J11 includes a test plug har- ness to facilitate vsm check–out.
- Page 19 V–TYPICAL OPERATING CHARACTERISTICS 3– With only the blower motor running and the evaporator coil dry, observe the manometer A–Blower Operation and Adjustment reading. Adjust blower motor speed to deliver NOTE– The following is a generalized procedure the air desired according to the job requirements. and does not apply to all thermostat controls.
- Page 20 16– Replace burners making sure to fully engage on C–Supply Air Blower orifice. Resecure burner mounting rail and flue box. Inspect flue box gasket. Replace gasket if Check and clean blower wheel. Motors are prelubricated necessary. for extended life; no further lubrication is required. 17–...
- Page 21 VII–WIRING DIAGRAM AND SEQUENCE OF OPERATION G25MV OPERATION SEQUENCE (FOR A MORE DETAILED DESCRIPTION SEE THE FLOW CHARTS ON THE FOLLOWING TWO PAGES): 1- When disconnect is closed, 120V is routed through speed. When the combustion air blower nears low or door interlock switch (S51) to feed the line voltage high operating speed, combustion air prove switches side of the ignition control (A3) and transformer (T1)
- Page 22 COOLING SEQUENCE OF OPERATION BURNER CONTROL LED: Slow flash rate. REMAINS UNCHANGED THROUGHOUT COOLING CYCLE. THERMOSTAT CALLS FOR COOLING. COMPRESSOR CONTACTOR AND BLOWER ENERGIZED. BLOWER ON HIGH SPEED. ON VSP2 “ON/OFF’” LED–DS3 IS LIT, “CFM” LED–DS4 BLINKS ONCE FOR EVERY 100 CFM. ACCA AND ACCH TERMINALS ON BURNER CONTROL BOARD ARE ENERGIZED.
- Page 23 NORMAL HEATING MODE HEATING SEQUENCE OF OPERATION BURNER CONTROL LED: SLOW FLASH RATE ABNORMAL HEATING MODE THERMOSTAT CALLS FOR HEAT (W1) BURNER CONTROL LED: FAST FLASH RATE LOCKOUT: MAIN VALVE OFF COMB. AIR AND SYSTEM FANS ON RESET THERMOSTAT FLAME OFF? BURNER CONTROL LED: 5 flash if flame sensed with valve off BURNER CONTROL LED: Steady on if control board failure CONTROL SELF–CHECK OKAY?
- Page 24 G25MV VSM BLOWER AND VSP2–1 BLOWER CONTROL BOARD TROUBLESHOOTING FLOW CHART DOES UNIT OPERATE? CHECK: 1–UNIT POWER IS 24VAC ACROSS 2–INTERLOCK SWITCH R AND C? 3–TRANSFORMER COOLING MODE 4–LIMIT SWITCH PLACE JUMPER ACROSS R AND G. IS BLOWER ON LOW SPEED AND IS “ON/OFF”...
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