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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
This article discusses the diagnosis & repair of backup heat systems used on heat pumps - how to find out if your backup heat is working or partly working, or not working at all.
This article series answers most questions about central air conditioning & heat pump system troubleshooting, inspection, and repairs. We describe how to inspect residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects.
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Diagnosing no backup heat working or not enough backup heat
If you are getting no backup heat at all, or the heat is inadequate, your system may not be switching on the backup heat at all, or it may be trying to switch on the backup heat but the backup heat is not working.
Diagnosing backup heat that turns on when it should not.
The following diagnostic tips were provided by a thoughtful reader, Neal Renn who describes the problem of a heat pump that insists on turning on backup heat when it is not needed. That is, during the cooling season, the heat pump insists on providing warm air rather than cool air to the building.
The family woke up to an 85 degree house even though the weather remained in cooling season. The occupants found that the heat pump system was running in heat mode. (A Goodman™ 5 ton heat pump and Goodman indoor air handler with propane backup heat.
see Detailed Case of a Heat Pump that Put out Heat when Cooling was Required for a step by step guide to diagnosing the cause of this particular "heat output only, no cooling" problem at a heat pump. Diagnostic details provided by a thoughtful reader, Neal Renn.
Here is a photograph of the heat pump outdoor thermosatt. It is housed in the control box corner of the outside heat pump compressor/condenser unit.
This heat pump outdoor unit has a control board, a contactor, a start capacitor and the outdoor thermostat which is used to determine when backup heat is needed.
Photographs courtesy of Neal Renn show a Goodman Manufacturing Corp. outdoor thermostat # OT18-60A (below left) and a back view of the control showing additional part numbers #B13708-66 (below right
For photographs of other air conditioning and heat pump parts, and for an explanation of where these air conditioning components are physically located, see A/C COMPONENTS which discusses Indoor A/C Components and Outdoor A/C Components
Since the failure of the heat pump's backup heat to turn on, loss of heating capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioning or heat pump system, after reviewing the lost backup heat diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below.
To return to our air conditioning, heat pump, and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.
If the backup heat source for your heat pump system is provided by an electric furnace, use the diagnostic details below when the backup heat is not working properly. This information is discussed further at ELECTRIC HEAT.
For economy, as Carson Dunlop's sketch shows, electric furnaces often use a gang of electric heating elements that are turned on in stages rather than all at once.
As temperatures fall and more heat is needed in the building, more heating stages turn on. By leaving heating stages turned off when not needed we reduce electrical consumption and energy cost.
On a staged electric heating furnace each heating stage typically provides about 5,000 watts (5KW) of heating energy.
The fan limit switch that controls an electric furnace may have a built-in delay so that on a call for heat the blower fan won't turn on until the heating element(s) have warmed up. We discuss fan limit switches in more detail at FAN LIMIT SWITCH
What do we check if our electric heat is not working? There are a few basic things to check yourself. Other steps require an expert. Sketches courtesy of Carson Dunlop.
If your air conditioning or heat pump system has lost its cooling capacity or won't start see
Continue reading at HEAT PUMPS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
(July 6, 2014) Anonymous said:
My mitsubishi mr.slim MUH-18RV have heating kit which were not working i bypass the kit and try to stat the compressor seperatly but when i try to start it try to start sounds and become heated , but could not start , before starting the compressor voltage are 212 VAC but when i start compressor voltages downs to 130 volts and all wires become hot . what is the problem is this due to bypass the compressor kit , or its motor is short ? please help me regards kalim ullah
Kalim it sounds like a seized compressor motor.
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