| InspectAPedia® |
InspectAPedia
| |
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair | Ask a Question or Search InspectAPedia |
Mobile ViewAIR CONDITIONING & HEAT PUMP SYSTEMS A/C - HEAT PUMP CONTROLS & SWITCHES AIR CONDITIONER BTU CHART AIR CONDITIONER COMPONENT PARTS AIR CONDITIONER TYPES, ENERGY SOURCES AIR CONDITIONER NOT WORKING AIR FILTERS for HVAC SYSTEMS AIR HANDLER / BLOWER UNITS APPLIANCE EFFICIENCY RATINGS BACKUP HEAT for HEAT PUMPS BLOWER DOORS & AIR INFILTRATION BLOWER FAN CONTINUOUS OPERATION BLOWER FAN OPERATION & TESTING BOOKSTORE - Air Conditioning "How To" Books CAPACITORS for HARD STARTING MOTORS CAPILLARY TUBES CHINESE DRYWALL HAZARDS CIRCUIT BREAKER SIZE for A/C or HEAT PUMP CLEANING & Legionella BACTERIA CHINESE DRYWALL HAZARDS COMBUSTION GASES & PARTICLE HAZARDS COMPRESSOR & CONDENSING COIL, A/C CONDENSATE HANDLING, A/C CONDENSATION or SWEATING PIPES, TANKS COOL OFF HEAT Thermostat Switch COOLING CAPACITY, RATED COOLING COIL or EVAPORATOR COIL COOLING LOAD REDUCTION by ROOF VENTS COMBUSTION GASES & PARTICLE HAZARDS CONDENSATE HANDLING, A/C CONDENSATION or SWEATING PIPES, TANKS DATA TAGS on AIR CONDITIONERS DEFINITION of Heating & Cooling Terms DEHUMIDIFICATION PROBLEMS DEW POINT CALCULATION for WALLS DEW POINT TABLE - CONDENSATION POINT GUIDE DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP DUCT SYSTEM & DUCT DEFECTS DUCTS - Asbestos DUCT INSULATION, Asbestos Paper DUCT INSULATION for SOUNDPROOFING DUCT SYSTEM NOISES DUCTS, Asbestos Transite Pipe DUST CONTAMINATION FROM HVAC? EDUCATION, HVAC SCHOOLS ELECTRIC MOTOR DIAGNOSTIC GUIDE ELECTRIC MOTOR OVERLOAD RESET SWITCH ELECTRICAL POWER SWITCH FOR HEAT EVAPORATIVE COOLING SYSTEMS EVAPORATOR COIL or COOLING COIL EXPANSION VALVES, REFRIGERANT FAN, AIR HANDLER BLOWER UNIT FAN AUTO ON Thermostat Switch FAN, COMPRESSOR/CONDENSER UNIT FAN CONVECTOR HEATERS - HYDRONIC COILS FAN LIMIT SWITCH FAN NOISES FURNACES WARM AIR HEATING SYSTEMS GAS EXPOSURE EFFECTS, TOXIC GAS DETECTION & MEASUREMENT GAUGE, REFRIGERATION PRESSURE TEST HEAT LOSS (or GAIN) in buildings HEAT PUMPS BACKUP HEAT for HEAT PUMPS HEAT PUMPS, GROUNDWATER HEAT PUMP STRATEGY - Indoors? HEAT PUMP Thermostats - Outdoors HUMIDITY LEVEL TARGET INDOOR AIR QUALITY IMPROVEMENT GUIDE INSPECTION CHECKLIST - OUTDOOR UNIT INSPECTION LIMITATIONS, A/C SYSTEMS LEED GREEN BUILDING CERTIFICATION LOST COOLING CAPACITY What to Check First A/C Flow Too Weak A/C Filter Problems A/C Compressor Problems A/C Off - Condensate Pan Switch A/C Cooling Coil Icing A/C Not Dehumidifying A/C Air Duct Problems Air Conditioner Won't Start Air Conditioner Refrigerant Problems Blower Fan No Start / No Stop Compressor Diagnosis: Diagnose & Repair Cooling Capacity of the Duct System Repair Guide Master List MANUALS & PARTS GUIDES - HVAC MOTOR OVERLOAD RESET SWITCH NOISE AIR CONDITIONER / HEAT PUMP OPERATING COST OPERATING DEFECTS OPERATING TEMPERATURES Air Conditioning System Temperatures Instruments Used to Measure A/C Temperatures Procedures for Making Temperature Measurements PORTABLE ROOM AIR CONDITIONERS PRESSURE READINGS, REFRIGERANT REPAIR GUIDE, AIR CONDITIONERS / HEAT PUMPS REPAIR & DIAGNOSTIC FAQs for A/C REFRIGERANTS GAUGE, REFRIGERATION PRESSURE TEST REFRIGERANT CHARGING PROCEDURE REFRIGERANT DRIERS & FILTERS REFRIGERANT LEAK DETECTION REFRIGERANT LEAK REPAIR REFRIGERANT METERING DEVICES TEVs REFRIGERANT METERING CAPILLARY TUBES REFRIGERANT PIPING & DISTANCES REFRIGERANT PRESSURE READINGS RETROFIT SIZING for A/C or HEAT PUMPS SEER RATINGS & OTHER DEFINITIONS SOLAR ENERGY SYSTEMS SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS SWAMP COOLERS SYSTEM OPERATION OPERATING CONTROLS THERMOSTATS, HEATING / COOLING Types of Building & Room Thermostats How Thermostats Work Detailed Guide to Room Thermostats How to Set the Thermostat COOL OFF HEAT Thermostat Switch FAN ON AUTO Thermostat Switch HEAT ANTICIPATOR Adjustment HEAT ANTICIPATOR Mini Ammeter to Check HEAT PUMP Thermostats - Outdoors INSTALL & WIRE Thermostats TEMPERATURE RESPONSE of Room Thermostats SWITCH FUNCTIONS on a Room Thermostat THERMOSTATIC EXPANSION VALVES WATER COOLED AIR CONDITIONERS More Information |
This website 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. Also see our list of heat pump inspection, diagnosis, and repair articles beginning at HEAT PUMPS. CONTACT us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. The articles at this website describe the basic components of an air conditioning system and then we discuss how to estimate the rated cooling capacity of an air conditioning system by examining various data tags and components. The limitations of visual inspection of A/C systems are described. We continue to add to and update this text as new details are provided. © Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. How to diagnose and fix the backup heat in a heat pump system that is not working is discussed at BACKUP HEAT for HEAT PUMPS. 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.
Detailed Case of a Heat Pump that Put out Heat when Cooling was RequiredThe following diagnostic details were provided by a thoughtful reader, Neal Renn. On my heat pump system, the thermostat is set for Normally Closed when the temperature is above the temperature setting. When the temperature drops, the contacts cycle. This is to pull in [turn on] the heat pump's backup heating system. When the thermostat lost it freon charge, the thermostat cycled and diverted to the emergency heat position. When the thermostat calls for emergency heat, it routes the request to the outdoor heat pump compressor to the white, heat control wire - always. This is for my system. The replacement thermostat used different terminal designations but worked the same way. The whole heat pump outdoor thermostat repair kit was $44 and was available for same day delivery. Heat Pump - Backup Heat Control Problem IdentificationIndoor heat request at the indoor thermostat only gets heat from the backup heat system not from the heat pump: when you request heat at the indoor thermostat, if you get heat from the backup heating system only, something is wrong with the outdoor compressor or with the heat pump controls. Normally when the indoor thermostat calls for heat, the heat pump will be used to provide heating until until the request is more than 2 Indoor cooling request at the indoor thermostat only gets warm air, coming from the heat pump's backup heater, and it's uncontrolled, that is, the system will heat forever. Heat Pump Backup Heat Control Problem DiagnosisThe first clue was that the heat came on while cooling (air conditioning) was requested on a heat pump system. If weather is intermittently cool enough that you might be calling for heat, this problem may remain hidden until warm weather makes you sure that your indoor thermostat should only be calling for cooling. Here are a couple of photos of the offending part. 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). When I first started looking at this, we thought the worst - a failed outdoor compressor unit. First try the indoor heat pump thermostat: the indoor wall thermostat was checked for proper settings (calling for cooling), but even though indoor temperatures were well above the indoor thermostat's cooling temperature set point, the heat pump would not operate. Next check the outdoor heat pump controls: Warning: removing the covers to access equipment controls can expose you to potentially fatal shock hazards. Do not attempt these steps unless you are properly trained. The diagnostician, (the owner in this case) pulled the cover from outside heat pump unit controls and pushed the contactor switch If the heat pump or air conditioning compressor runs in response to this step when it would not turn on in response to the thermostat it is natural to next suspect a problem with the heat pump controls, not the compressor unit itself. (There are exceptions such as a hard starting compressor that might sometimes start easily but have trouble starting against a head pressure when it was just turned off moments before.) Investigating the heat pump controls further: being sure that the " heat only" problem was a control problem - either in the wall thermostat (indoors) or in some other control the owner tried swapping in another thermostat (in this case the old, original mercury unit). The result was the same symptoms, un-changed. Checking the heat and backup heat controls: That's when the owner started digging into the dual fuel kit and its wiring. Diagnosing a gas-charged outdoor heat pump thermostat sensor problem: This heat pump unit was installed originally in 1993. The old outdoor thermostat was a B13708-66. That thermostat was later superceded by a Goodman™ B13708-67. Mr. Renn wrote: the more I think about the uncontrolled heat issue when the thermostat loses it's charge, I'll bet Goodman reversed the contacts in the replacement control so that it will simply not turn on the heat pump compressor and you get NO heat on a thermostat failure. I have not confirmed this - but from a safety standpoint, it would make sense. We left our house unattended for two months in the summer while the family traveled. If this failure would have happened unattended, we would have had a burned up furnace, minimum, house most likely. Replacing the outdoor heat pump thermostat involved a "bolt-on" replacement part, connecting wires according to the manufacturer's instructions, and testing the unit again. What caused the failure of the outdoor heat pump thermostat? a plastic nut holding the supply line to the inlet
valve. The nut was cut with a sharp edged relief at the base of the
thread - which defined a nice - "break here" mark. Immediately the owner
replaced all supply nuts with brass (only had 2 that were not). He observed that another of these plastic connecting nuts appeared ready to fail like the first. He also
finally installed the pressure regulator for the house and cut the line 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 your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
Questions & Answers regarding this article. Ask a Question or Search InspectAPediaHTML Comment Box is loading comments...
Recommend / Share this Article
... Technical Reviewers & References
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. AIR CONDITIONING & HEAT PUMP SYSTEMS
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
|