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Frost blocked cooling coil (C) Daniel FriedmanAir Conditioner / Heat Pump Inspect & Repair
Home Page & Index to Diagnostic Procedures

This page provides an index to key articles describing air conditioner & heat pump inspection, installation, troubleshooting & repair procedures, parts, manuals & codes.

This air conditioner & heat pump inspection, installation, diagnosis & repair article series explains in detail the purchase, installation, inspection, troubleshooting diagnosis, and repair of all types of residential and light commercial central air conditioning and heat pump systems.

Page top image & air conditioning schematic drawing below were provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Air Conditioner / Heat Pump Installation, Troubleshooting, Repair

Loose blower assembly pulley or belt reduces airflow (C) Carson Dunlop Associates

Since the failure of an air conditioner to turn on, loss of air conditioner cooling 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 conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures listed 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.

Just below we give brief descriptions of the main types of trouble you may encounter with an air conditioner or heat pump. For each of these possible trouble areas.

For air conditioner or heat pump troubleshooting that can be done by many building owners or occupants, see our separate article

DIAGNOSTIC GUIDE A/C or HEAT PUMP - first steps to diagnose an air conditioner or heat pump.

For more detailed troubleshooting, you can see our list of COMMON A/C OR HEAT PUMP DETAILED DIAGNOSTIC PROCEDURES found below on this page.

Air Flow Problems in Air Conditioning or Heat Pump Systems

Weak or no air flow coming out of the supply registers in each room. Often the problem is as simple as a dirty air filter or dirty indoor blower fan in the air conditioner or heat pump air handler unit.

Cooling Problems in an Air Conditioner or Heat Pump

If there is good air flow out of supply registers but in cooling mode the air does not get cool, or in heating mode (for heat pumps) the air delivered does not get warm the trouble could be that the outdoor compressor unit is not working or that the system has lost its refrigerant charge.

Electrical problems at A/C & Heat Pumps

Many service calls for non-working air conditioners or heat pumps turn up an electrical problem.

The most basic electrical problem is that a motor or HVAC unit simply won't start. Other electrical problems include buzzing noises at relays or burning electrical smells.

But first remember to check the system power switches at the air handler indoors, at the compressor/condenser outdoors, and in the electrical panel.

If your A/C system is just not working at all, be sure to check all of our electrical and control setting suggestions first.

Indoor Air Handler / Blower Problems on HVAC systems

Besides weak air flow that we mentioned above, more serious problems such as a failing blower motor or no a blower fan that never starts at all can prevent the delivery of cooled or heated air.

Mechanical problems on HVAC systems

We see a number of problems with fans and fan motors in both the compressor/condenser unit and in the air handler/blower fan unit. Some of those fan problems are mechanical - like a loose fan belt or blade.

A more simple mechanical problem is an air supply or return duct that has become disconnected, loose, crushed, or leaky, leading to the failure of the A/C or heat pump system to deliver air to supply registers. We class these as duct system problems.

Outdoor Compressor/Condenser Unit Problems on Air Conditioners or Heat Pumps

The unit has at least two motors: the sealed compressor motor that compresses refrigerant gas so that it can be condensed back to liquid form, and a fan motor that spins the fan necessary to move outdoor air across the condenser unit coils.

An outdoor compressor/condenser unit may refuse to start, may be noisy, or may fail to do its job to compress the system's refrigerant from a gas back to liquid form.

Control relays, boards, switches in the condenser unit may fail, or a refrigerant leak at the unit can cause loss of cooling or heating even though the indoor blower unit delivers air at the supply registers.

Common A/C or Heat Pump Detailed Diagnostic Procedures

Honeywell room thermostat

If your air conditioning or heat pump system has completely lost cooling capacity or if it plain won't start you can jump right

to DIAGNOSTIC GUIDE A/C or HEAT PUMP for our complete list of diagnostic procedures, or select one or more of the focused diagnostic articles listed below.

In that article we step through basic troubleshooting steps that most building owners or occupants can do - DIY Quick Repairs for A/C or Heat Pumps.

A longer list of commond dagnostic procedures are listed below:

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-05-30 by Ben - new cooling coil doesn't fit my existing indoor air handler

I need to replace my A/C on the outside of my house and the evaporator coil. My problem is that my existing furnace has a 13in wide evaporator coil and I can't find that size anywhere. The smallest I can find are 14 and 14.5 inch. Can I use a bigger evaporator coil on my furnace? What would be need to do so? Thank you!

On 2023-05-30 by InspectApedia Publisher (mod) - Upflow furnace installation of an add-on cooling coil or evaporator coil

@Ben,

Yes you can use a larger evaporator coil, but be sure to discuss with the installer just how the air plenum should be shaped for best air flow across the coil.

Watch out: if your new coil is too large for the system's design it may cool the building without adequate dehumidification (because it cools everything down too fast to complete moisture removal).

The transition plenum that you install will be shaped to direct air flow across the coil without creating dead air spaces.

Don't just slap on a larger coil atop the air handler, sticking out at the sides.

Here is an often-quoted excerpt from Trane's IO manual

FURNACE UPFLOW INSTALLATION

Standoffs and screws (See Figure 1, page 6) are included with the cased coils for attachment to the furnace. NOTE: The top flanges on the furnace must be bent 90 degrees upward to allow the coil attachment.

There are clearance alignment holes near the bottom of the coil wrapper. Drill screws are used to engage the furnace top flanges. The standoff is inserted into the cabinet alignment hole.

The drill screws are inserted through the standoffs then screwed into the furnace flange. The coil is always placed downstream of the furnace airflow. The above instructions apply only if the coil is on top of an upflow furnace.

COIL

a. Apply gasket material (duct seal field supplied) to ALL mating surfaces between the furnace and the coil case.

b. Set the coil case on top of the furnace. Connect the ductwork to the coil case using the field supplied screws.

c. Secure the coil case to the furnace and seal for air leaks as required.

Question: how do I figure out the replacement for my old AC Compressor Capacitor

Old AC compressore capacitor terminals compared with new ones (C) InspectApedia.com StephenRetail

Retail Stephen

Wondering if anyone can figure out the replacement for my old ac capacitor. The newer says HCF (Herm, common" Fan) but based on the wiring diagram it shows BCA. Please help!! Please see pictures attached - 2022/08/18

Old AC compressore capacitor terminals compared with new ones (C) InspectApedia.com StephenRetail

Moderator reply:

Sure - the values are right on the cap, but you can also follow the steps at

CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS

or if you need help wiring it up

MOTOR CAPACITOR WIRING GUIDE

You'll see that it's pretty straight forward: 3 wires, Common, Fan, & Compressor.

Old AC compressore capacitor terminals compared with new ones (C) InspectApedia.com StephenRetail


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Or see AIR CONDITIONING & HEAT PUMP SYSTEM FAQs - questions & answers posted originally at this page.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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