There are several variables that influence the point at which the fans are shut off, such as outdoor air temperature, return air temperature, whether the unit is an HRV or ERV, system size and cfm, use of boost mode, etc. The unit is programmed to monitor all of these variables, and depending on the combination of factors it' s possible for the fans to be shut off anytime the outdoor temperature is below freezing. But in general, an HRV with an internal pre-heater can function normally down into the 20' s (F) and an ERV down into the teens. It' s possible for the units to function at even lower temperatures depending on the variables mentioned earlier.
Zehnder offers more robust pre-heater options for customers in especially cold climates. Please contact your Zehnder technical sales representative for more information.
The most common source of an A7 error code is when a unit with an internal pre-heater turns off the fans because the temperature has dropped below the safe operating limit. This is exactly what we want the unit to do in these conditions so that the HRV or ERV core doesn' t freeze. The pre-heater works to avoid or delay a necessary shut-down, but if the temperature gets cold enough even the pre-heater isn' t enough to protect the core, so the fans will be turned off. Because this is the desired function, the A7 isn' t so much an error code as it is a notification. The unit is programmed to periodically check the air temperatures and resume normal operation when it' s safe to run. But even after the fans are running again the A7 notification will remain on the controller to alert the user that there has been a shut-down. To clear the code, simply unplug the HRV/ERV for a minute or so and plug it back in.
There may be other, less-common reasons for an A7 code, so if the code persists be sure to contact your Zehnder service technician.
When installed according to the applicable Zehnder America, Inc. Installation instructions and the applicable local, state, and federal building codes and unless specified otherwise, all Zehnder America, Inc. products sold in North America carry a two (2) year LIMITED WARRANTY (from the original date of shipment by Zehnder America, Inc.) covering defects in the original manufacture. The warranty does not apply to damage from accident, misuse or alteration; or where the equipment has been improperly installed, improperly wired, improperly maintained or connected to an improper voltage in violation of the product' s installation and operating instructions. This warranty is null and void if the product was improperly installed or operated incorrectly at any time. All claims for warranty work must be sent by certified mail and must be accompanied by proof of the date of purchase.
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