Heating, Air Conditioning, Fridge, HVAC/Short Cycling


My residential hvac has short cycling only when using ac. the outside compressor comes on steady when cooling is called by tstat. inside home basement,at furnace,the evap fan(maybe incorrect word)short cycles. This short cycling motor is NOT the fan blower that circulates air through the vent ducts.
In heat mode, gas forced air furnace works fine with warm air blowing out ducts. When a/c is called for from tstat, compressor outdoors runs steady. however, inside I can hear a fan(?) attempting to start for 1 to 2 seconds. that cycle repeats until I turn the tstat off. The ventilation fan blower will run fine when tstat is set for heat or fan "ON".  It never gets the chance to start when a/c is called because the other motor in the furnace can be heard short cycling.
The a/c was started last evening about 8p.m. for the 1st time since last summer. It cooled the house just fine until this morning i noticed the subject motor short cycling (heard sound thru vent ducting on main floor). I turned tstat setpoint lower to make sure there wasn't cycling due to closeness of setpoint to actual room temp. Cycling continued. I slid tstat mode control from cool to heat, raised the tstat temp for heat and all worked fine. This is when I noticed the short cycling motor is not the air blower motor or the outside compressor.  Any suggestions before I call for help. I am comfortable using a fluke dmm. I have electrical experience, just not hvac.  i hope my description isnt too wordy or confusing to understand. i apologize if that is the case. thanks


You seem to be describing the ventor motor/ purge motor for the flue gas removal, if so and that is what's coming on during heat  ( short cycling ) try  marking your thermostat wires at the thermostat and pull all wires off of thermostat ( would need a narrow blade screwdriver.  ) first turn power off to the furnace.  Then turn power back on after you removed the wires,  start with jumping the R and g wire , only your indoor blower fan should run, if so then connect the Y to the R and G. Only the A/C and indoor blower should run, if so , pull wires apart making sure none of the bare wires touch. Then put R wire to W only your heat should run, you may have to hook up the G wire to bring on the indoor blower.  If all is well you probably have a bad thermostat.

Heating, Air Conditioning, Fridge, HVAC

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.


Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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