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Scott, HVAC Technician
Category: HVAC
Satisfied Customers: 398
Experience:  30 yrs. experience as self-employed HVAC Service Technician. Universal EPA Certification, NATE Certified, Trane Service One, ACCA ACE Certified.
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I am a service tech with 49 yrs. experience in all genre of

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I am a service tech with 49 yrs. experience in all genre of HVAC systems from absorption equipment to current refrigerant types. One of my customers has two (both identical) conventional R-22 split A/C systems with Apollo hydronic fan coil units. The 2nd story air handler (located in the attic) has hot water migrating thru the coil reducing the air temprature differential in the cooling mode to -4 degrees. The inlet to the water coil is fairly hot but I have checked to insure that the circulating pump is not running and there are no water leaks in the return piping that may allow flow thru the coil. The A/C side of the system is operating properly and the 1st floor system is functioning perfectly. What am I missing!

Hello this is Scott,

I have had this happen before, but it only seems to happen with units above the water heater, My 2 thoughts are the a failed checkvalve in the pump or a failing zone if the air handler has one. In the problem units I had I installed hard shutoff ball valves at a location convienient to the homeowner.


Customer: replied 4 years ago.

Thanks Scott - the Apollo unit is equipped with factory installed shut off valves which I have closed while I determine how to resolve the problem. This is not a zone system but the unit is located above the water heater. Could it be relevant that prior to this past heating season the homeowner installed a new high end hydro / potable specific water heater ? (Never had a problem before). Also, If I am unable to come up with another resolution and to promote simplified customer operation of the unit, would installing a low voltage n/c solenoid valve in the supply water side of the coil be advisable. Should the valve be activated by the thermostat system switch (leaving the valve open while in the heat mode) or opening on a call for heat? Mike ([email protected] or [email protected])

Hi Mike

The Apollo heaters are designed so that hot water doesn't migrate so if it was replaced with a different
heart style then the installation of a 24v zone valve on the inlet of the coil it should open on the call for heat. Honeywell valves are a good choice as they power open and spring close and are easy to install.
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