As an HVAC technician it is not uncommon to find bad capacitors that are the primary reason for a trouble call from a customer for their air conditioner or heating system not working. A good HVAC technician can usually figure out the problem very fast simply by listening to the symptoms of what the unit is doing in the sequence of operation whether it is the air conditioner sequence of operation, the gas furnace sequence of operation or in the heat pump sequence of operation. Typically in the order of sequence of operation of any of the aforementioned pieces of equipment a motor is not working properly and this leads the technician to the problem when troubleshooting the problem.
Checking to make sure the capacitor is the problem is often easy for a trained HVAC technician. Bad capacitors can often be identified by looking at the capacitor. Often when a capacitor goes bad it swells up the outer casing and sometimes blows the top off the capacitor leaving an oily residue around the capacitor and in the control panel where the capacitor is located. Sometimes this is not the case and the capacitor needs to be tested with a special multimeter that has the function to test capacitors.
Before testing a capacitor when troubleshooting capacitors the capacitor needs to be discharged as capacitors hold an electrical charge and can shock you even when they are not hooked up to any electrical wiring. The capacitor is discharged using a high resistance resistor (over 10,000 Ohms). This is very important to do as if it is not done the test instrument can be damaged. Once it has been discharged the capacitor can be tested. The instrument measures microfarads which are how capacitors are rated. The test should fall within plus or minus 10% of the rating on the capacitor. If it is out of this range then it needs to be replaced with a new capacitor of the same microfarad rating.
Troubleshooting HVAC Capacitors
A few years ago it was rare that I got an email asking the question about how inverters work but now I have noticed the question coming more and more so I wanted to write an article to explain how inverters work. Inverters are used in air conditioning to modulate 
Hello and Thank you for emailing High Performance HVAC, Dorothy, Your registers should not be closed off as it is bad for the unit. The unit was installed based on the size of your home and the needed airflow for the house. This is designed airflow and requires all registers to be open to get the designed airflow through the unit and all the ducts. Closing off registers restricts airflow and is the same as a dirty filter which restricts airflow and causes problems with the unit. I have seen this before and I cover this on the HVAC filter page. In a gas pack it will cause excessive heat build up inside the unit and cause the unit to trip on high limit safety if you close off too many registers as the required airflow is not moving across the heat exchange so the heat continues to build up in the heat exchanger and eventually trips this high limit safety. Leave all your registers open and make sure you have a clean filter to maximize the unit. The best way to get the most efficiency out of the unit is to get a programmable thermostat and run the unit only as necessary. For more information on this see the thermostat pages concerning programmable thermostats and there use. Additionally, making sure you have good windows and doors to minimize heat loss will also help. Adding insulation to your attic space and other areas will also help reduce the amount the unit runs will result in savings and additionally having a humidifier installed will also help you remain comfortable in the winter time. For more information on why a humidifier will help you remain more comfortable in the winter see the humidifiers page.
Richard Many thanks for your very prompt response! What you say ties in with what I read regarding stress on the unit. However, this Victorian “cottage” is 3,000 sq. ft. w/ 12 ft. ceilings is now too big for only my husband and I. Is there not a way we can isolate the unused space and save on heating without stressing the unit? We have done all that you suggested. Storm windows, doors, etc., except for the attic insulation. The company that installed the unit is no longer in business and the man that I got to service it after that died. last fall. I’m in a very small town and the nearest Heil dealers seem to be 40 or more miles away. I did print a list of those I found. Haven’t called any yet as I ran across your webpage. My final question is, given the size of the unit, could I convert to 2 zones somehow? And, only heat the occupied part in winter? Thanks for you patience and help.
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