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BTU VENTILATION CORPORATION ● OFFICE 888-884-8070 ● FAX 218-346-7485 ●
www.btucorp.com
XT-70 Control Panel 23
HMI OUTSIDE AIR CONTROL:
five minutes.
CAT Cooling Air Timer. The CAT timer comes into play when the system terminates Cooling and
goes into Standby mode. The default setting is three minutes. The CAT timer will start timing as
soon as the system switches to Standby. This is a countdown timer, and once it reaches 0, the
system will determine if the outside air temperature is below the start temperature. The system
will go back into the Cooling mode if cooling is available. The CAT timer has an override condi-
tion - when the outside air is 3° less than the start temperature, the CAT will not be in affect.
RAS Plenum Rise Above Setpoint. The default setting for the RAS is .3°. This is used to determine
when cooling air is no longer available. If the plenum temperature is higher than the RAS setting
and the outside air temp is higher than the start temperature, the system will terminate cooling.
Summary of Cooling Air Logic:
Cooling air available If OSA < Start_T and CAT satisfied or if (OSA - 3) < Start_T.
Cooling air not available If OSA > Start_T
Terminate Cooling Run If OSA > Start_T and Plenum temp > RAS and MCR satisfied.
The FORCE COOLING button can be used to force the system into a cooling mode. The time clock must be set
to allow cooling. Once the system is in cooling, it will run for the minimum cooling time.
The FORCE REFRIG button can be used to force the system into a refrigeration mode. The time clock must be
set to allow refrigeration. Once the system is in refrigeration, it will run for the minimum refrigeration time.
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