Harris Atlas DVL400 Technical Manual page 143

Section 4 Theory of Operation
ATLAS Series™
4.6.4.4.2 Latching Relay K9
When the transmitter is turned ON, a relay on the External I/O board for Pump A or
pump B is closed (depends on the previous operating condition). This supplies the
+34Vdc from the control panel back through X2 pin 4 or 5 to latching relay K9.
Since K9 is shown in Remote mode, the +34Vdc passes through K9 to K1 if Pump
A is to be selected or K2 if Pump B is to be selected. The +34 volts to K1 or K2 is
diode steered via V6 or V7 to also activate K5. K1 would activate Pump A via
contactor K3. K2 would activate Pump B via contactor K4. K5 will turn on the heat
exchanger fans via contactors K1 and K2 when the coolant temp rises sufficiently.
4.6.4.4.3 K5, Heat Exchanger Control Relay
K5 has 2 paralleled contacts which supply 24Vac to connector X5 pin 14. This is
connected to X2 pin 19 which is the connection point out to the heat exchanger
connector X1 pin 15. 24Vac is now present at the thermal switches AQ1 and AQ2 in
o
the heat exchanger. AQ1 will close when the coolant temperature reaches 32 C.
o
AQ2 will close when the coolant temperature reaches 38 C.
4.6.4.4.4 Fan A Control and Status
When AQ1 closes, it supplies the switched 24Vac to the coil of fan contactor K1 at
X3 pin 9. K1 has 4 contacts, K1.1, K1.2 and K1.3 are in series with the 3 phase ac to
the fan A motor. K1.4 is connected between X3 pin 3 and X4 pin 3 and is used to
light the Fan A ON Status LED, H1G. However, the +34Vdc to light the status LED
passes through the 4th pole of the isolator switch on the heat exchanger, S1,
preventing an active status LED if the isolator switch is open.
4.6.4.4.5 Fan B Control and Status
When AQ2 closes, it supplies the switched 24Vac to the coil of fan contactor K2 at
X3 pin 10. K2 has 4 contacts, K2.1, K2.2 and K2.3 are in series with the 3 phase ac
to the fan B motor. K2.4 is connected between X3 pin 4 and X4 pin 4 and is used to
light the Fan B ON Status LED, H1I. However, the +34Vdc to light the status LED
passes through the 4th pole of the isolator switch on the heat exchanger, S2,
preventing an active status LED if the isolator switch is open.
2/25/03 888-2473-001 4-43
WARNING: Disconnect primary power prior to servicing.