Timers; Thermostatic Snap Switches - Cleveland steamcraft 21-CET-8 Service Manual

Timers

Figure 5-9. Timer

Thermostatic Snap Switches

Low voltage, below about 90 VAC, will cause the solenoid to hum loudly or chatter.
Check transformer secondary for 120 VAC nominal. Check for loose connections.
The resistance of a good solenoid coil measures about 600 ohms.
The SteamCraft 3.1 solenoid valves operate at a maximum pressure of 60 psi.
Higher pressure causes unnecessary valve wear and requires frequent valve
replacement. If necessary, install a pressure regulator set at 50 psi.
If an electronic key pad timer or mechanical dial timer fails the SteamCraft 3.1 can
usually be operated in MANUAL mode (TIMED/MANUAL switch set to MANUAL).
This allows continued operation while waiting for a replacement timer.
The 3-minute timer (all units) and the 3-second timer (mechanical timer only)
operate identically except for the time delay. When 120 VAC is applied across
terminals 2-3 (INPUT), the timer circuits provide 120 VAC across terminals 1-3
(LOAD). When the time. elapses (3 minutes or 3 seconds), the timer sets the LOAD
terminals to 0 VAC.
A timer contains electronic components which work like a relay and contact Refer to
Figure 5-9. When the switch doses, the timing circuit (shown as a relay and contact)
energizes. The timing circuit doses its contact to energize the solenoid. When the
delay time of the timer elapses (3 minutes or 3 seconds), the tuning circuit opens
the contact and the solenoid deenergizes.
A load most be connected to the LOAD terminals of the timer during testing. Use a
spare solenoid or buzzer as the test load. Without a load connected to the LOAD
terminals, the voltage across the LOAD terminals will read 120 VAC when the timer
energizes and will remain at 120 VAC indefinitely.
Because the LOAD terminals remain energized only for a short time, connect the
voltmeter across the LOAD terminals before energizing the timer and leave it
connected during the test. Watch for the LOAD voltage to read 120 VAC when the
timer energizes and 0 VAC at the end of the proper delay (3 minutes or 3 seconds).
Thermostatic snap switches, the high temperature limit switch that protects the
heater elements and the compartment temperature thermal switch (electronic timer
units only) can be tested by voltage or resistance measurements. Closed switches
should always measure 0 ohms. Resistance of any open switches should always
measure infinity.
Model 21-CET-8 Service Manual Page 79
Printed 12/90