SERVICING TIPS FOR BTU AND OTHER DUCT HEATERS

NO HEAT

1 Check that the controlling T'Stat is set to call for Heating. If the T'stat has a Fan Switch, check the ON position. If the Fan runs, you have learned there is power to that section and the Transformer, Fan Relay and Motor are apparently OK Return Fan Switch to the Auto position for checking out the Heater next.

2. The Heater should be checked only by qualified service personnel who know how to safely check that there is Power and Control Voltage to the Heater. After that various components can be checked with a Continuity Meter with ALL HIGH VOLTAGE POWER OFF. Replace parts that have failed but remember the following:

• An open Fusible Link or Manual Reset is usually caused by a stuck contactor that allows Heater to "run on" after T'stat is satisfied and the Fan goes off.
• Our U.L. Label is voided and liability passes from us when other than an exact replacement part is used or an Approved Alternate Listed in our U.L. Procedure. The same holds true it any safety device is by-passed. All parts are readily available from our Distributor or on "ship today" basis from our plant.

NOT ENOUGH HEAT

1 . Check that the Ampere draw is reasonably close to that on the Heater data plate. If that is not feasible, check Heat Rise against Performance Formula. Some systems have slower Fan speed on Heating so calculate Heat Rise accordingly. You shouldn't be more than 10% short on either check unless the Supply Voltage is lower than the Heater Data Plate rating or part of the Heater is not operational. Replace any non4unctioning parts with EXACT BTU PARTS or Approved Alternates listed in our U.L. Procedure.

2. A Heater that cycles off before the Thermostat is satisfied may cause complaints only during the coldest days when maximum performance is required. (See Section on "Heater Cycling" on back of this page.)

3. Thermostat with Heat Anticipator current draw set too low will "short cycle" a Heater off before the set temperature is reached and when maximum running time may be required. Be sure to figure the extra components that may be energized during the defrost cycle on Heat Pumps. DO NOT FORGET that other than exact replacement components may require a change in the Heat Anticipator setting.

4. If the shortage of heat is in only some areas you might have a condition that requires seasonal damper adjustments to balance differing ratios of Heat Loss and Heat Gain. A kitchen may require proportionately more summer cooling than winter heating. A recently crushed or broken duct would affect a particular area. Also restricted airflow usually affects rooms at the end of the duct system first.

5. TIP: Your customer may have turned on the heat after the area had gotten cold and expected it to warm up quickly or may have made some preliminary checks before calling you. Discharge Air with a low Heat Rise blowing on a 98*F. hand or face might seem like the system wasn't working properly or that there was no heat at all. This is a typical complaint in southern climates or in commercial applications 9 the Heat Rise is relatively low. If the system is functioning properly, you will have to educate your customer to turn on the Heat before it gets so cold. U.L. Listed "Zero Clearance" Duct Heaters are more acceptable than those with more Heat Rise but without Zero Clearance to combustible surfaces. Maintaining a satisfactory Heat Level on the coldest days, with safety, is the primary concern.

HEATER CYCLING ON AUTOMATIC LIMIT

1 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.

2. Improper airflow caused by obstructions to Return Air, Loose or Broken Fan Belt, Clogged Filters and/or Evaporator Coils may cause the Limit Switch to cycle Heater off before T'stat is satisfied and could cause riot enough heat in general or just in the "end of the line" rooms because of the reduced pressure in the duct system.

3. Improper Installation -with insufficient or uneven airflow over the entire Heater. Borderline installations may start cycling after Coil, Filter and Blower get dirty. Heaters are designed not to nuisance cycle provided that sufficient velocity and thickness of inlet air curtain flows between the Primary Limit and Heating Element. The LIL rule for Duct Heaters to be located 4 feet downstream from an A/C unit and 2 feet before or after an elbow has its place in elimination of nuisance cycling. Some other conditions that contribute to cycling of a Heater are listed below:

• Heater in a large plenum but too close to a small blower prevents even airflow.
• Baff les bouncing air off Heating Element onto Limit Switch can add to problem.
• Base of Heater Controls Box not flush with the air stream reduces air curtain
• Heater connected to higher than rated voltage results in Superheated Elements.
• Installing Heaters in the top of a horizontal duct is not authorized. Primary Limit Switch cut-out point is lowered by its location on top.

OPEN SECONDARY PROTECTIVE DEVICE

1 An open Manual Reset, Fusible Link or other Secondary Thermal Device is usually the result of a stuck Coritactor where the Tstat is satisfied and there is no more Fan. The Heater "runs on" in this abnormal condition until the Secondary Device opens.

2. Lack of proper air over the Heater could cause enough cycling of the Limit Switch so that a Secondary would open after a build up of enough residual heat. This is particularly so when a Heater is installed from the top of the duct.

3. 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.

CONTACTOR CHATTER

1 . Improper Wiring

2. Insufficient Transformer Capacity (This may occur during defrost on some heat pumps when many extra components are temporarily energized OR if chatter happens after a component substitute change the substitute may draw more VA overloading the transformer.)

3. Vibration or Contamination of Mercury Thermostat.

4. Excessive Static Pressure on an open face Limit Control (Rare)

ELEMENT FAILURE (Not prevalent if properly designed and not abused)

1. Excessive overheating with wrong temperature or by passed Primary Limit Control.

2. Improper installation with enough air directed over the Primary Limit to keep the Heater operating but severely overheating other places not getting enough air.

3. Improper filtering so that Elements can not dissipate heat through dirty covering.

4. Corroded hardware or loose connections causing bumed-off wires or Elements.

5. Any physical damage, grounding, a nick or an impurity in the Element itself.

6. Bad Element Design with too much KW in a given space and/or riot enough Element mass to dissipate heat. The hotter an Element operates, the quicker It deteriorates.

7. Very light gauges of Element wire may be sufficient electrically but they simply flutter in the high velocity air until they are grounded out and burn through.