High Efficiency Furnaces - PDF Free Download

High Efficiency Furnaces Presented By 777 Education and Consulting, Inc. Lansing Michigan Instructor Marcus Butch Metoyer, Jr., CMS, MS, CGP 1

Instructor Bio. HVAC contractor/business owner 40+ years Technical instructor for Behler-Young (HVAC): 29 years Community college instructor (HVAC): 10 years B.S. & M.S. degrees from M.S.U. (construction management - CM) M.S.U. CM instructor: 5 years part time, 10 years full time EPA Clean Air Act Registered Proctor RSES CMS designation NAHB CGP designation NATE Certified 2

Safety Verify voltage is off before touching any electrical circuits don t assume switches work verify. Ronald Reagan: trust but verify. Follow all Federal OSHA, state OSHA, RSES, test /tool / and equipment manufacturer s safety instructions and precautions. 3

ANSI Categories of Appliances Gas Appliances *Categories. Vented gas appliances are classified for venting purposes into four categories as follows: Category I Category II Category III Category IV * The following Category definitions apply to the appliance and do not necessarily reflect the performance of the connected vent system. 5

Category I An appliance that operates with a non-positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent. May include draft hood and fan-assisted appliances. Vented with Class B or a lined masonry chimney system if allowed by local codes. These systems have AFUE ratings of 55 70% for older furnaces, boilers, and water heaters, and up to 78 82% for newer systems. Venting to be done with Gas Appliance Manufacturer s Association (GAMA) tables, or the manufacturer s instructions: whatever your local code requires. 6

Category II An appliance that operates with a non-positive vent static pressure and with a vent gas temperature that may cause excessive condensate production in the vent. 7

Category III An appliance that operates with a positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent. 8

Category IV An appliance that operates with a positive vent static pressure and with a vent gas temperature that may cause excessive condensate production in the vent. These appliances are typically 87 97% efficient and are vented with plastic, stainless steel, or a material which is other than Class B or masonry. Vent installation must follow manufacturer s instructions: GAMA does not apply. 9

Ignition Systems Standing Pilot Remote Sensing Spark Ignition (IID, DSI) Local Sensing Remote Sensing Hot Surface Ignition (HSI) Local Sensing Remote Sensing 10

Sensing Flame Standing Pilot Thermal (thermocouple, thermopile, bimetal) Spark Ignition (IID, DSI) Thermal (mercury filled, bimetal) Flame Rectification Hot Surface Ignition (HSI) Flame Rectification 11

Standing Pilot Old technology Flame detection is thermal Slow response to flame failure Less safe than more modern systems Spark ignition Hot surface ignition 12

Spark Ignition Intermittent Ignition Device (IID) Lights pilot first. May have been approved by A.G.A. for 100% or non- 100% shutoff for Nat. Gas. Must be 100% shutoff for L.P. Test lockout on all units employing IID Direct Spark Ignition (DSI) All fuels require 100% shut off (lockout) Test lockout function on all units, every time Short trial for ignition period (<10 seconds) 13

Hot Surface Ignition Hot Surface Ignition (HSI) Direct ignition system (except Honeywell Smart Valve) All fuels require 100% shut off (lockout) Test lockout function on all units, every time Short trial for ignition period (<10 seconds) 14

Gas Valves AGA requires redundant gas valves on all units. What is redundant? There are two ways to stop main gas flow, instead of one. Some incorporate a pressure switch. 15

PV MV MV/PV = Pilot Valve = Main Valve = Common TH-TR (PV) 24V TERMINAL STRIP TH (MV) TR (MV/PV) Common Gas Valve Body PV MV Pilot Tapping Inlet Outlet Typical IID Redundant Gas Valve Simplified Schematic Both Valves Closed - No Power To Either Copyright 2006-777 Education and Consulting, Inc. - All Rights Reserved = Gas Pressure 17 1

TH-TR (PV) 24V TERMINAL STRIP TH (MV) TR (MV/PV) Pilot Tapping PV MV Inlet Outlet Typical IID Redundant Gas Valve Simplified Schematic Pilot Valve Open & Main Valve Closed PV to MV/PV Receiving Power From Control Copyright 2006-777 Education and Consulting, Inc. - All Rights Reserved = Gas Pressure 2 18

TH-TR (PV) 24V TERMINAL STRIP TH (MV) TR (MV/PV) PV MV Pilot Tapping Inlet Outlet Typical IID Redundant Gas Valve Simplified Schematic Pilot Valve & Main Valve Open PV - MV/PV & MV - MV/PV Are All Powered From The Control Copyright 2006-777 Education and Consulting, Inc. - All Rights Reserved = Gas Pressure 19

MV 24V TERMINAL STRIP MV C Gas Valve Body MV MV Inlet Outlet Typical DSI/HSI Redundant Gas Valve Simplified Schematic Both Valves Closed - No Power To Either Copyright 2006-777 Education and Consulting, Inc. - All Rights Reserved = Gas Pressure 20

Methods Of Flame Sensing Thermal Standing Pilot IID Spark Ignition Flame Rectification IID DSI HSI 22

+ + + + + + + + + + + + Flame Rectification No combustion here Pos. / Neg. (Sensor) + / Outer Cone - burning zone Inner Cone - mixture too rich to burn Negative Probe (Burner/Ground) Sensing Circuitry Sensing Transformer Figure 1 23

Ignitor/Sensor (+/ ) Pilot Burner Ground ( ) Warning: do not attempt to read flame signal in the ignitor/sensor wire. Combination Igniter/Sensor 24

Ground ( ) Separate Ignitor and Sensor 25

Flame Rod AC Voltage Flame Rod Rectified Current Pulsating DC Flame Signal 26

Transformer 24 Volt Secondary R W Thermostat Limit Pilot Burner Ground 25V 25V MV/PV PV MV GND Igniter/Sensor Terminal Igniter/Sensor Local Sensing PV MV MV/PV IID Redundant Gas Valve Copyright 2006 - All Rights Reserved 27

Warning When selecting a IID, DSI, HSI, or Standing Pilot replacement control, follow the manufacturer s recommendations explicitly. OEM is your best bet. 28

Where To Place Micrometer With Local Sensing System? In Series With Ground Wire, Unless Directed Differently By Manufacturer. 29

Limit Thermostat Note: limit may be in the 115 volt circuit not the 24v circuit. Measuring Flame Signal Typical IID Spark Ignition Controller Uses Combination Ignitor/Sensor Ignitor/Sensor Connection 24V 24V MV MV/PV PV Local Sensing GND DC : Amps Volt/Ohmmeter Set To Read DC : Amps 1:A = 1/1,000,000 Amps =.000001 Amps PV MV/PV MV Redundant IID Gas Valve Read DC :A after the spark has stopped. Steady :A reading must exceed the mininum indicated by the manufacturer of the control. Complete system must be grounded WARNING Follow ALL manufacturer's instructions without exception. 2005 - All Rights Reserved 777 Education and Consulting, Inc.. 30

Transformer 24 Volt Secondary R W Thermostat Limit Remote Sensing Pilot Burner Ground Sensor Igniter 25V 25V MV/PV PV MV Sensor GND Igniter Terminal Remote Sensing PV MV MV/PV IID Redundant Gas Valve Copyright 2006 - All Rights Reserved 31

Where To Place Micrometer With Remote Sensing System? In Series With Sensor Wire, Unless Directed Differently By Manufacturer. 32

Limit Therm ostat Note: limit may be in the 115 volt circuit not the 24v circuit. Measuring Flame Signal Typical IID Spark Ignition Controller Uses Separate Sensor & Ignitor Spark Connection 24V 24V MV MV/PV PV GND Sensor Remote Sensing DC : Amps Volt/Ohmmeter Set To Read DC : Amps 1:A = 1/1,000,000 Amps =.000001 Amps PV MV/PV MV Redundant IID Gas Valve Read DC :A after the spark has stopped. Steady :A reading must exceed the mininum indicated by the manufacturer of the control. Complete system must be grounded WARNING See the warnings and instructions on the other side of this page. 2005 - All Rights Reserved 777 Education and Consulting, Inc. 33

Replacement Parts ALWAYS follow the manufacturer s instructions to the letter. No over-thinking is allowed. 34

S8610U Honeywell Universal IID Replacement Local or Remote Sensing Capable 35

S8910U Honeywell Universal HSI Replacement Local or Remote Sensing Capable 38

S8910U - HSI Personality plug (selection tab). 39

Slide 41

White-Rodgers Typical HSI Controller With Remote Sensing Legend GV = Gas Valve IGN = Igniter FP = Flame Probe TH = Thermostat GND = Ground H = Hot 115V C(N) = Common or Neutral MV = Main Valve TR = Transformer L1 = Hot 115V Copyright 2006 777 Education and Consulting 42

GE ECM by Regal-Beloit Courtesy of: GE ECM by Regal-Beloit 44

GE ECM / Regal-Beloit / Genteq About the Company In 1987 General Electric introduced ECM technology to the residential HVAC industry. This technology is predominantly used in variable speed indoor blower motors, constant speed induced draft motors and condensing fan motors. These innovative motors changed the industry by providing unmatched efficiency as well as comfort options not possible with PSC induction motors. In 2004 the Regal Beloit Corporation acquired General Electric s Commercial and HVACR Motors and Capacitors businesses with the right to use the GE brand through 2009. These divisions were named GE ECM by Regal Beloit, GE Commercial Motors by Regal Beloit and GE Capacitors by Regal Beloit. In 2009, Regal Beloit announced the rebranding of those GE branded businesses under the name Genteq, 45

https://www.thedealertoolbox.com/tools/ecm-service-guide/ 49

ECM Electronically Commutated Motor Provides constant air flow (CFM) by adjusting speed and torque of motor as static pressure changes. Will not overcome more than approximately.9 in w.c. Uses less electricity than shaded-pole or permanent split capacitor (psc) motors. Can be programmed by the O.E.M. to provide low speed constant fan operation. Is a 3-phase motor which runs off single-phase power. May be 120V or 240V. 50

Constant Fan Factory programmed to operate at about 50% to 60% of cooling CFM. Operation selected by the consumer at the thermostat ( FAN ON ). Typically operates at 60-90 Watts vs. Induction motor at approx. 400-700 watts. Provides continuous air filtration and more even air temperatures from room to room (de-stratifies the air). In some climates constant fan is not recommended due to re-humidification. 51

ECM vs Induction Motor 600 550 Courtesy of: GE ECM by Regal-Beloit High Winding Input Power (Watts) 500 450 400 350 300 250 200 150 100 35 Watts ECM Induction Low Winding 280 Watts Induction motor needs over 130 Watts more power than GE ECM 50 0 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Motor Speed (RPM) Greater power shedding - Cut ECM speed in half and power consumption drops by a factor of 8 Courtesy of: GE ECM by Regal-Beloit 52

Power The motor will operate properly with input power ±15% of nominal. Low voltage will effect motor performance but will not harm the motor. Motor may turn on and off if voltage is too low. The motor control is connected to line voltage at all times. Standby power on average is approximately 2-3 watts. 53

The Line Voltage (high voltage) Power Connection The 120vac input uses a jumper (red wire) The 240vac input does not use a jumper Caution: proper jumper connection is required. 5-pin Power connector Courtesy of: GE ECM by Regal-Beloit 54

About The Jumper The motor will operate from an input voltage of 120/240vac When 240vac is used for input power, the jumper must be removed. Caution: If the jumper is not removed when 240vac is applied to the motor control, the motor will be permanently damaged. 55

Then and Now The History of the GE ECM ECM 1.0 1987 Hardware Programmable Basic Constant Airflow Algorithm Often called the ICM-1 (Integrated Control Module) ECM 2.0 1992 Complete Motor and Control Design Torque Calibrated machine Refined Airflow Regulation Algorithm Motor is the airflow sensor Late point Product Identification - Software programmable Often called the ICM-2 (Integrated Control Module) Courtesy of: GE ECM by Regal-Beloit 56

ECM 2.3 1998 Response to reliability improvement Control Electronics and packaging redesign Electronics encapsulated for moisture resistance New motor controller ASIC Improved performance and features Sometimes called the ICM-2+ ECM 2.5 2002 Digital Serial Communication Enables plug & play HVAC systems Fewer replacement part numbers More accurate operation and fault reporting Courtesy of: GE ECM by Regal-Beloit 57

The ECM Technology (overview) The ECM motor is a brushless DC, Three - phase motor with a permanent magnet rotor. Motor phases are sequentially energized by the electronic control, powered from a single-phase supply. Input power supply 120/240vac (Caution: proper jumper connection) Motor control converts AC power to DC power Motor control determines speed and torque to maintain airflow to OEM specifications Motor control converts DC power back to AC three-phase power for motor operation ECM - Electronically Commutated Motor Models 2.3 & 2.5 Courtesy of: GE ECM by Regal-Beloit 58

Motor Control Construction Microcomputer module Power Conditioning module The microcomputer module is encapsulated with a polyurethane compound to protect against moisture Courtesy of: GE ECM by Regal-Beloit 59

Stator Construction ECM Laminated, interlocked stator Steel shell, aluminum end shield, through-bolt construction Available in a closed, partial, or fully vented shell PSC Courtesy of: GE ECM by Regal-Beloit 60

ECM Rotor 3 Iron Ferrite magnets glued on rotor sleeve Magnetized at GE Factory Two Resilient Rings isolate the shaft from the rotor Ball Bearings Rotor Construction Resilient Ring PSC Rotor Not permanently magnetized Hard mounted to the shaft Sleeve bearings Courtesy of: GE ECM by Regal-Beloit 61

The ECM motor is basically a 3-Phase motor operated by a motor control. Motor Control 3-Phase AC motor Courtesy of: GE ECM by Regal-Beloit 62

GE ECM Troubleshooting Generic troubleshooting follows. Specific troubleshooting instructions must be obtained from the OEM. 63

Input power (High Voltage) to the motor controller Pull on connector not the wires Input power can be 15% range of the nominal 120vac or 240vac Check polarity when input power is 120vac 120vac 240vac 64

With the main power restored, check the power at the 5-pin connector as shown Meter connected between Terminal #5 and #4 Meter connected between Terminal #5 and #3 120vac AC Volts 120vac AC Volts 5 4 3 2 1 ~ V Com ~ V Com Ground AC Line AC Line Courtesy of: GE ECM by Regal-Beloit 65

With the main power restored, check the power at the 5-pin connector as shown Meter connected between Terminal #5 and #4 Meter connected between Terminal #5 and #3 Meter connected between Terminal #4 and #3 240vac AC Volts 120vac AC Volts 120vac AC Volts ~ V Com ~ V Com ~ V Com Courtesy of: GE ECM by Regal-Beloit 66

Checking the motor control and motor module TECInspect 67

Motor Module Tests Test A measure the resistance between each of the 3 motor leads to the unpainted part of the end shield. If the motor fails (the resistance is <100k ohms) then replace the motor module with the equivalent. If the motor module passes (the resistance is >100k ohms) then perform Test B. Courtesy of: GE ECM by Regal-Beloit 68

Motor Module Tests Test B measure the motor phase-to-phase resistance by checking these combinations of the 3-pin motor connector with an ohmmeter. For the purpose of this test, start at either end of the connector as Lead 1. 1. The lead to lead resistance across any two leads should be less than 20 ohms. 2. Each lead to lead resistance should be the same within ± 10%. If the measured resistance is outside the range, then the motor module needs to be replaced with an equivalent. Courtesy of: GE ECM by Regal-Beloit Lead 1 to Lead 2 Lead 1 to Lead 3 Lead 2 to Lead 3 69

When replacing the motor module Make sure the belly band is not covering any vents Control module orientation may dictate motor orientation Tighten the wheel key on flat side of motor shaft with wheel centered If the wheel sits too close to the motor when centered or cannot be centered because it hits the motor, the motor must be adjusted in the belly band Courtesy of: GE ECM by Regal-Beloit 70

Attaching the new control module Insert the 3-pin connector back into the new control module. A slight click will be heard when inserted properly. If replacing an ECM 2.0 control with an ECM 2.3 control, insert plastic tab Into perimeter of replacement control and align tab with mating hole in the end shield. Use the new shorter bolts provided to ensure a secure attachment. Orient the Control to the end shield between 4 & 8 o clock, insert bolts and tighten. Courtesy of: GE ECM by Regal-Beloit 71

Attaching the new control module Cont. If replacing an ECM 2.3 with an ECM 2.3, orient the new control to the motor s end shield with connectors facing down, insert bolts and tighten. Reinstall the blower/motor assembly into the HVAC system by following the manufacturer s guidelines. Plug the 16-pin connector and the 5- pin connector back into the motor. Make sure the keyed connectors are inserted properly and securely until they click. Courtesy of: GE ECM by Regal-Beloit 72

Be certain to form a drip-loop so that water cannot enter the motor by draining down the cables. Condensate or droplets can accumulate in the harness and may find their way into the motor. Final installation check. Ensure the system is setup as follows: (a) (b) (c) (d) Verify the condensate drain is not plugged or clogged. Reconnect the AC power to the HVAC system and verify that the new motor control module is working properly. Check and plug leaks in return ducts and equipment cabinet. The system should run quietly and smoothly. Courtesy of: GE ECM by Regal-Beloit Note: If this is a repeat failure, then it is important that you check the following: Any evidence of moisture requires correcting the issue. If this area is subject to high amounts of lightning strikes, the use of additional transient protection may be helpful. Visit www.thedealertoolbox.com to learn more. 73

E.S.P. 74

Return air from the home Supply air to the home Return Grille Supply Registers Balancing Dampers Ductwork +.35 in. wc -.15 in. wc. 0-.5-1- Air Filter Measuring E.S.P. Courtesy of: GE ECM by Regal-Beloit and Christopher Mohalley, President, HVAC Dynamics 75

-.15 +.35 -.4 -.3 -.2 -.1 0 +.1 +.2 +.3 +.4.50 in. w.c. External Static Pressure (ESP) 76

2006 Flue Loss Supply Gas Cock Output Cabinet Losses Input Return Output = Input - Flue Loss -Cabinet Losses 77

Air Temperatures Return Air Temperatures (measure in the blower cabinet will take into account bypass humidifier leaks, outdoor air intake, return air duct leaks, etc.). Minimum (often 55 O F / 60 O F) Maximum (often 85 O F) Temperature Rise (measure return air in the blower cabinet and supply air in a supply trunk or branch, 3 feet from the supply plenum) Minimum Maximum Obtain from rating plate. 78

(Intermittent or continuous) Min. / Max. Return Air Temperature Example shown above: follow manufacturer s recommendations. 79

... furnace is designed for minimum continuous return air temperature of 60 F db or intermittent operation down to 55 F db. Return air temperature must not exceed 85 F db. From Bryant model 311AAV furnace installation and Start up manual. Other models and manufacturer s specs. may vary. 80

Model Returns Return requirements. 4. Airflows over 1800 CFM require bottom return, two---side return, or bottom and side return. A minimum filter size of 20 x 25 is required. 5. For upflow applications, air entering from one side into both the side of the furnace and a return air base counts as a side and bottom return. 82

Temperature Rise Temp Rise = Supply Temp - Return Temp Supply Temperature (After running 10 minutes) 3 Air Flow Direction Gas Cock Gas Valve Burners Return temperature Air Filter 2005 777 Education and Consulting, Inc. All Rights Reserved 83

Natural Gas Pipe Sizing Sch. 40,.5 psi gas pressure,.3 w.c. pressure drop per 100, 84

85.5 psi 13.89 w.c. 2015 IFGC

Using Temp. Rise To Calculate CFM BTU Output Of Furnace CFM = ----------------------------------------- 1.08 X Temp. Rise Rules: limit must not cycle the burners off at any time, altitude of installation is between 0 and 1,000 feet above sea level, input is set precisely according to manufacturer s instructions (proper manifold pressure and orifice size), 86

CFM Example After the supply temperature stabilizes, your supply temperature is 106 O F and the return air temperature is 65 O F. Furnace is 80,000 input (gas pressure and orifices are correct), 72,000 output. Temperature rise shown on the rating plate is 35 65 O F. Question: is the temperature rise O.K.? 87

Example Continued Yes! Calculate CFM Do this math first. CFM = Output (1.08 X Temp. Rise) = 72,000 (1.08 X 41) = 72,000 44.28 = 1,626.02 88

Input, 2 nd Method Clock the meter to determine CFH (cubic feet of gas per hour). Pick smallest dial you can easily time for 1 complete revolution. Determine btu/cubic foot (BTU/CF) for the gas provided by your utility. Formula: 3600 X Dial Size CFH = Seconds Per Rev. 89

Meter Clocking (continued) Furnace or boiler input in BTU/Hr. Input = CFH X Heat Content of 1 CF Utility says heat content of their natural gas is 1,000 BTU/CF. 90

1/2 Cu.Ft. 1 Cu.Ft. 2 Cu.Ft. 5 Cu.Ft. Typical Gas Meter 2006 777 Education and Consulting, Ltd. 91

Meter Clocking (continued) Example: Dial Size selected is.5 cubic feet (cu. ft.) Time for 1 revolution is 18 seconds CFH = (3,600 X.5) 18 = 1,800 18 = 100 CFH Input = CFH X Heat Content per Cu. Ft. = 100 X 1,000 = 100,000 92

Setting Manifold Pressure (Nat. Gas) Verify inlet line pressure Determine outlet (manifold) pressure using: Heat content of one CF Altitude above sea level Specific gravity of the fuel Burner orifice size Used to calculate manifold pressure 93

2015 IFGC 95

Proper Venting Follow manufacturer s instructions. 96

Wiring Diagram Basics There are 2 types: Ladder (used mainly for service and determining the sequence of operation). Also called a schematic by some. Pictoral (used to show the location of components and provide a point-to-point wiring diagram). Difficult to use to determine sequence of operation. 97

PICTORAL DIAGRAM LADDER DIAGRAM 98

Category IV IID 90% AFUE Ladder Diagram L1 115 Volt Fused And Protected L2 Power Supply BDS SSU Switch Fused Disconnect Switch FR1 (NC) FR2 (NO) IMR1 Fan Sw. Line Voltage (115V) Low Voltage (24V) Heat Speed A/C Speed B M IM Common Tape Off Unused Speeds Separately Primary Transformer Htg./Clg. Stat ROS LIMIT FL Secondary GND Y G W R R IMR2 IMR IID Spark Box With Pre-Purge Timer W TH G C PS TR MV MV Y IMR3 PV PV Low Voltage Terminal Strip FR MV/PV Spark Gas Valve GND CC Copyright 2005 All Rights Reserved 777 Education and Consulting, Inc. 99

LEGEND BDS Blower Door Switch BM Blower Motor DSG Draft Safeguard Switch (manual reset) FL Fusible Link (3A) GND Ground IM Inducer Motor IMR Inducer Motor Relay LIMIT High Temp. Limit (auto reset) MV Main Valve MV/PV Common PS Pressure Switch PV Pilot Valve ROS Roll Out Switch (manual reset) TH Power IN From Transformer (Trans.) TR Common To Trans. 100

L1 115 Volt Fused And Protected L2 Power Supply SSU Switch Fused Disconnect Switch Line Voltage (115V) Low Voltage (24V) BDS FR1 (NC) Fan Sw. Heat Speed A/C Speed B M Common FR2 (NO) Tape Off Unused Speeds Separately IMR1 IM Transformer 24 V Copyright 2005 All Rights Reserved 777 Education and Consulting, Inc. 101

Htg./Clg. Stat Y G W R Transformer ROS LIMIT FL 115 V 24 V GND DSG R IMR2 IMR IID Spark Box With Pre-Purge Timer W TH G C PS TR MV MV Y IMR3 PV PV Low Voltage Terminal Strip FR MV/PV Spark Gas Valve GND CC Copyright 2005 All Rights Reserved 777 Education and Consulting, Inc. 102

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Maintenance FOLLOW ALL MANUFACTURER INSTRUCTIONS the following is generic information only Inspect and change as necessary: Vent, drain, and duct system Heat exchangers Wiring and connections Filters All accessories Thermostat 104

Maintenance (Continued) Clean: Burners Blower wheel and motor Check: Safety lockout on all systems All system safety components Check for presence of CO and gas/oil leaks 105

Maintenance (Continued) Check (continued) : Combustion air Negative mechanical room pressurization Venting system Draft inducer and pressure switch operation Temperature rise Manifold pressure Flame with fan off, then with fan on Heat exchangers for holes or cracks For combustibles near the appliance 106

Maintenance (Continued) Complete all manufacturer recommended items Make recommendations to customer Run unit through a complete cycle COLLECT 107

Things To Watch Out For Temp. rise out of range. Gas pressure not set to mfg. specs. Secondary fin tube heat exchanger is dirty they make great air filters. Condensate leaks (furnace or evaporator coil). Low t stat set point. (For example, minimum recommended return air may be 55 O F intermittent / 60 O F continuous) 108

Useful Tips All Equipment Get equipment manufacturer s operation and service instructions before you need them. (Obtain full model, product, and serial numbers). Get web addresses. Get component manufacturer s name and part number off parts which you are not familiar with. Order the instructions before you need them. Get web addresses. 109