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Mobile View AIR CONDITIONING SYSTEMS AIR CONDITIONER BTU CHART AIR CONDITIONER COMPONENT PARTS AIR CONDITIONER TYPES, ENERGY SOURCES AIR CONDITIONER NOT WORKING AIR FILTERS for HVAC SYSTEMS AIR HANDLER UNITS BACKUP HEAT for HEAT PUMPS BLOWER DOORS & AIR INFILTRATION BOOKSTORE - Air Conditioning "How To" Books CLEANING & Legionella BACTERIA COMPRESSOR & CONDENSING COIL CONDENSATE HANDLING CONTROLS & SWITCHES COOL OFF HEAT Thermostat Switch COOLING CAPACITY, RATED COOLING COIL or EVAPORATOR COIL DATA TAGS on AIR CONDITIONERS COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ DEFINITION of Heating & Cooling Terms DEW POINT CALCULATION for WALLS DEW POINT TABLE - CONDENSATION POINT GUIDE DUCT SYSTEMS DUCTS - Asbestos DUCT SYSTEM DEFECTS DUCT INSULATION, Asbestos Paper DUCT INSULATION for SOUNDPROOFING DUCTS, Asbestos Transite Pipe DUST FROM HVAC? ENERGY SAVINGS in BUILDINGS EVAPORATIVE COOLING SYSTEMS FAN AUTO ON Thermostat Switch HEAT LOSS (or GAIN) in BUILDINGS HUMIDITY LEVEL TARGET INSPECTION CHECKLIST - OUTDOOR UNIT INSPECTION LIMITATIONS LOST COOLING CAPACITY What to check first Compressor failure diagnosis Duct & Air Handler diagnosis MOTOR OVERLOAD RESET SWITCH OPERATING COST OPERATING DEFECTS OPERATING TEMPERATURES Air Conditioning System Temperatures Instruments Used to Measure A/C Temperatures Procedures for Making Temperature Measurements REPAIR GUIDE for AIR CONDITIONERS REPAIR & DIAGNOSTIC FAQs for A/C REFRIGERANTS REFRIGERANT LEAK DETECTION REFRIGERANT LEAK REPAIR SEER RATINGS & OTHER DEFINITIONS SYSTEM OPERATION OPERATING CONTROLS THERMOSTATS 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 CRITICAL DEFECTS on A/C SYSTEMS More Information InspectAPedia Blog - News Updates Air Conditioning & Heat Pumps Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure Accuracy & Privacy Policies Contact Us |
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. 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. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links 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. 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 SYSTEMS. If your air conditioning system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
... 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 SYSTEMS
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