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14. Service Relay
14.1. Service Relay Operation
The M3 Unit Controller Service Relay output (A55_P298-8) default operation indicates that service is required.
If the default operation is not required, the Service Relay output may be used as a control output. Use Parameter 186 to
choose the input which will trigger the Service Relay output. The formula X + (32
x
Y) + (16
x
Z) is used to select the option.
See table 55.
If Parameter 186 input sources 7-9 are used, the set point and dead-band must be set with Parameter 187, Parameter 188,
Parameter 189, Parameters 190, 191 and 192.
Table 55. Service Relay Options
Control Parameter Control Value
Unit Description
No. Screen Name Min. Default Max.
186 SRV OUTPT CTRL MODE
Service Output
Control Mode
0 0 127 Option
A55 Service Output Control Mode = X + 32*Y + 16*Z
Input source = X:
0- None. Standard Service Output based on
alarms.
1- Compressor 1 duty cycle. (Compressor
crankcase heater function.)
On when Outdoor Air Temperature is
less than or equal to Parameter 189 and
greater than or equal to Parameter 192
seconds have passed with compressor
1 off.
Off when Outdoor Air temperature is
greater than Parameter 189 plus 3°F
(fixed dead-band) or is less than
Parameter 192 seconds have passed
with compressor 1 off
2- On when occupied.
3- On when blower on,
4- On when heating demand.
5- On when cooling demand.
6- On when heating or cooling demand.
7- System Relative Humidity Monitor (see
section 14.2. for further details).
(A55_P298_5 RH)
8- System Indoor Air Quality Monitor (see section
14.3. for further details). (A55_P298_5 RH)
(A55_P298_3 IAQ)
9- System Outdoor Air Temperature Monitor
(see section 14.4. for further details).
(A55_P267_1/2 OAT)
10- Energy Recovery System
11- SCR Option for Electric Heat
Algorithm Y for input sources 7-9:
0- Hysteresis loop (see sections 14.2 - 14.4)
1- Window - On when input is in range; (see
sections 14.2 - 14.4)
2- Delayed-on. (see sections 14.2 - 14.4)
3- Delayed-off. (see sections 14.2 - 14.4)
Inversion Z:
0- Output not inverted.
1- Output inverted.
Note: Inversion is not applicable to X=0 i.e.
Service relay use for alarms:
187 SRV OUTPT SP C02
Service Output
Set Point for
Carbon Dioxide
0 996 2000 ppm A55 service relay output set point.
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