Hartzell CD15K - 11.4 TROUBLESHOOTING - HEATER ACCESSORIES; 11.4.1 Overheat switch; 11.4.2 Combustion air pressure switch; 11.4.3 Ignition

2900 Selma Highway, Montgomery AL 36108 USA
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MM10001
Dated 1/1/08
Rev L dated 5/21/15
11.4 TROUBLESHOOTING - HEATER ACCESSORIES
11.4.1 Overheat switch
These switches are mechanical and typically have automatic reset after cool-down of
approximately 3-5 min. Switch terminals are numbered 1, 2 & 3. Terminals 1 & 3 are
normally closed.
 If no voltage is coming out of auto-reset switch, but has power to it, replace
switch.
11.4.2 Combustion air pressure switch
With combustion air blower running, check both sides of combustion air pressure switch
to see if voltage is present.
 If voltage is to switch, but not out, yet airflow is constant out of exhaust, check
switch setting or replace.
11.4.3 Ignition
• If rated voltage present at ignition power at terminal 2(10), remove power from
heater.
 Remove lead from spark plug and, using rubber-handled pliers, hold lead
approximately 1/4” from shroud of heater.
 Turn heater on and observe spark. It should be strong, blue and constant.
• Weak or no spark (1) check ignition lead under ceramic tip at plug end and coil end.
Replace if arcing is evident. If arcing is found on lead, also check spark plug
insulator where ceramic end of lead is housed.
• Spark plug has a fixed gap setting and should only be cleaned using M.E.K. or
cleaning solvent. NEVER sandblast.
• Verify lead is secured properly to both the ignition unit and igniter plug. Torque at
igniter plug is 15-20 ft. lbs. and ignition unit, 12-15 ft. lbs.
11.4.4 Adjustable duct (thermostat) (See Figure 31A & B)
Red wire - power in, blue wire - power out, black wire - ground, yellow wires – to
thermostat control. (0 to 10 OHMS resistance)
 Voltage to (red wire), but is less coming out (blue wire), or erratic in operation,
replace switch.
11.4.5 Cycling/Limit switch (See Figure 31A & B & C & diagnostic chart)
NOTE: See heater and or CD21252 installation instructions
11.4.5.1 General description
The CD21252 operates as an upper limit cycle switch, adjusted to cycle the
heater off at 250˚F regardless of how high the duct switch is turned up in the
cockpit. The upper limit of the heater is adjusted and set at the time of assembly
and testing is done at the factory. However, final adjustment can be made upon
final installation of the heater.