HVAC Heating System Controls

Assignment #1

• Thermocouple and Thermopile are two components that produce electricity when heated.
• Ignition controls supervise the operation of a gas fired appliance.
• Thermostat, Fan controls, and Aquastat are three types of operating controllers.
• Safety controllers are normally closed.
• Hi-limit, Flame roll-out, and Door switch are three types of safety controllers.
• Continuous, Intermittent, and Interrupted are three types of pilots.
• Interrupted, Direct spark, and Hot surface are three types of ignition control modules.

Module 12

• Two causes for induced draft switch failure can be a plugged vent and an inducer that is not working.
• A licensed plumber can change a low water cut-off.
• The maximum operating pressure for a commercial steam boiler is 15 psi.
• The maximum voltage generated by a thermopile is 750 mV.
• An open circuit thermocouple test will produce 20-30 mV.
• Pilot drop out voltage is between 2-4 mV.
• In a thermopile system, a thermostat without an anticipator will have a voltage drop of about 10 mV max.
• A combination gas valve includes a pilotstat, main & pilot regulator, and a main valve.
• A flame roll-out is a snap action disk.
• A diaphragm valve is slow opening and fast closing.
• A solenoid valve is a fast opening and fast closing valve.
• Most ignition controls have a flame failure response time of 0.8 seconds.
• Combination gas valves have a pilot gas valve in line with the main gas valve.
• A flame rod should project 1/2" inch into the flame.
• A thermocouple should project 3/8 to 1/2 inch into the pilot flame.
• The ground must be at least 4 times the surface area of the flame rod.
• The flame safeguard control will read a pulsating direct current from a flame rod system.
• A noisy lifting pilot flame is caused by high gas pressure.
• Excessive draft at the pilot location will cause a waving blue flame.
• The process of conduction of electricity through a flame is called flame ionization.