Trouble Shooting Alarms - Hussmann Proto-Aire Installation Manual

meter to the two outside pins. The voltage present at these two pins should
be between 20 and 27 VAC. If the secondary voltage is within limits
replace the control board. If the secondary voltage is out of limits,
investigate supply voltage to the control transformer.
Problem D: Temperature Sensor is not reading properly.
The temperature sensor used on Protocol™ is typically used to sense discharge air
temperatures at the evaporator load. The sensor contains a NTC (Negative Temperature
Coefficient) thermistor, which will increase resistance as temperature falls and decrease
resistance as temperature rises.

Trouble Shooting Alarms

The following section gives information on diagnosing specific alarms. The first step in
analyzing alarms is to determine when the alarm occurred. The alarms will appear in the
controller. The cause, time and date of the alarm will be shown.
There are two types of alarms: switchback and non-switchback. A switchback alarm is
normally the result of some external failure as seen or interpreted by the electronic control.
When a switchback alarm occurs, the electronic control removes itself from control of the
compressors. Operation and cycling of the compressors will be controlled by a low
pressure mechanical switch located inside the Protocol™ system, which will cycle one half
of the compressors. The indication of alarm will be dependent upon which alarm device
has been installed: auto dialer, in store alarm or computer system. Note that under a
switchback alarm no defrosts will occur. There are three types of switchback alarms: (1)
High Suction Pressure, (2) Low Suction Pressure or (3) All compressors off for more than
60 minutes.
All other types of alarms fall under the "non-switchback" category, such as high discharge
temperatures. The control will continue to cycle compressors and manage defrosts under
this category of alarms.
Alarm: High Suction Pressure
This alarm is one of the three "switchback" alarms. The time delay for this condition is 30
minutes. High suction pressures are ignore during defrosts.
Possible Causes
One or more compressors are operational.
High alarm limit is not set properly.
Step 1 Enter the Alarm Menu. Observe the time and date of the alarm. You will be
prompted as to whether or not you want to clear the current alarm.
Protocol™ Installation and
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Service Manual