Click here to make tpub.com your Home Page

Page Title: Heater Cycling on Automatic Limit.
Back | Up | Next

Click here for thousands of PDF manuals

Google


Web
www.tpub.com

Home


   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Logistics
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
   
   

 

TM 55-1905-223-24-17
(d) If the shortage of heat is only in some areas you might have a condition that requires seasonal
damper adjustments to balance differing ratios of heat loss and heat gain.  A galley may
require proportionately more summer cooling than winter heating. Crushed or broken duct
would affect a particular area. Also restricted air flow usually affects rooms at the end of the
duct system.
(e) Turning on the heat after the area has gotten cold and expecting it to warm up quickly is a
common complaint. Discharge air that has a low heat rise might feel, as it blows on a 980F
hand or face, as though the system is not working properly or as though there is no heat at all.
(3) Heater Cycling on Automatic Limit.
(a) The possibility of a defective or wrong temperature limit switch is always there, but more often
than not other conditions contribute to a heater cycling problem.
(b) Improper air flow caused by obstructions to return air, a loose or broken belt, or clogged filters
and/or evaporator coil, may cause the limit switch to cycle the heater OFF before the
thermostat is satisfied. This could cause a lack of heat in general, or just in the end-of-the-line
rooms, because of the reduced pressure in the duct system.
(c) Uneven air flow over the entire heater. Heaters are designed not to nuisance-cycle, provided
that a sufficient velocity of inlet air flows between the primary limit and heating element. Some
other conditions that contribute to cycling of a heater are as follows:
1
Heater too close to the blower outlet.
2
Baffles bouncing air off heating element onto limit switch.
3
Base of heater control box not flush with the air stream (reduces air curtain).
(4) Open Secondary Protective Device.
(a) An open manual reset, fusible link, or other secondary thermal device is usually the result of a
stuck contactor where the thermostat is satisfied and there is no more fan. The heater runs on
in this abnormal condition until the secondary device opens.
(b) Lack of proper air over the heater could cause enough cycling of the limit switch so that a
secondary would open after a buildup of enough residual heat.
(c) Grounded heating element may generate enough heat without fan to open a secondary.
Overcurrent fuses or circuit breakers may or may not open, depending on the amount of
element resistance to ground and the amount of related current it draws.
2-30

Privacy Statement - Press Release - Copyright Information. - Contact Us

Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business