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There is a bank of 8 dip switches, (See Figure 15), located at the upper right side of the board. The dip switches work in pairs to match the cooling/heat pump airflow (CFM/TON), Fan off-delay options, and electric heat airflow adjustment. The switches appear as shown in Figure 15. Page 15 t DIP SWITCHES (TYPICAL SETTINGS) ICM FAN CONTROL CFM SELECTION LIGHT DIP SWITCHES DEMAND DEFROST SYSTEM PIN IDENTIFICATION FRC_DFT DEFROST CONTROL The demand defrost control measures heat pump outdoor ambient temperature with a sensor located outside the outdoor coil. A second sensor located on the outdoor coil is used to measure the coil temperature. The difference between the ambient and the colder coil temperature is the difference or delta-T measurement. This delta-T measurement is representative of the operating state and relative capacity of the heat pump system. By measuring the change in delta-T, we can determine the need for defrost. The coil sensor also serves to sense outdoor coil temperature for termination of the defrost cycle. FAULT DETECTION A fault condition is indicated by the flashing light on the defrost TEST_COMMON TST DEFROST CONTROL CHECKOUT control inside the heat pump control box. Normal operation requires: In normal operation, the defrost control light will flash once each a. LED on board flashing 1 time/second. second. If the light is flashing more than once per second or not-atall, refer to the service manual for that unit. b. 24V AC between R & B c. 24V AC between Y & B with unit operating PIN IDENTIFICATION (See Figure) 1. TEST_COMMON (Shorting any of the other pins to this pin d. Defrost initiation when FRC_DFT pin is shorted to causes the function of the other pin to be executed. Leaving this TEST_COMMON pin. pin open results in the normal mode of operation.) If a defrost control problem is suspected, proceed to DEMAND 2. TST = Test (Shorting TEST_COMMON to this pin speeds up DEFROST CONTROL CHECKOUT in this Service Facts. all defrost board timings.) 3. FRC_DFT = Forced Defrost (Short TEST_COMMON to this pin Do NOT connect 24 VAC to T1 ^ WARNING: for two (2) seconds to initiate a forced defrost. Remove the short (ODS-A) terminal. ODS-A thermistor WILL BE BLOWN. after defrost initiates.) PROCEDURE FOR TESTING SENSORS TEMP °F RESISTANCE Measure the temperature the subject sensor is exposed to. If the sensor is mounted on a 86 7.85K tube, place the lead on an Annie A-8 (or equiv.) temperature tester on the same tube near 81 8.85K the sensor and insulate the bulb. 75 10.24K 70 11.59K Unplug the sensor and measure the resistance with a good quality ohmmeter (Simpson 65 13.14K 260 or equiv.). Read the value as quickly as possible to prevent the meter current from 59 15.32K changing the resistance reading. 55 16.93K Using the chart on the right, locate (as close as possible) the actual sensor temperature. 50 19.41K The measured resistance should be relatively close to the resistance value shown in the 45 22.20K chart. 41 24.76K Example: 36 32 28.45K 31.84K Sensor temp. = 19°F. 25 37.50K Measured Resistance = 46K ohms 19 14 46.44K 53.94K This sensor is good since the measured value is relatively close to the 10 57.64K chart value. 5 67.06K 0 78.05K FLASH RATE INDICATIONS: 1 — Flash/Second = Normal operation. 2 — Flashes/Second = Fault A (Low .T) i.e.: Inoperative compressor, loss of charge, open ambient sensor, shorted coil sensor. 3 — Flashes/Second = Fault B (20 defrosts terminated on time) Fault C (High .T) i.e.: SOV stuck in heating, shorted ambient sensor, open coil sensor, closed TXV, OD motor failure, OD fan on in defrost, undercharged unit. 4 — Flashes/Second = Fault A & C or A & B For additional information consult Pub. No. 34-1001 Heat Pump Defrost Controls. Page 16 DEMAND DEFROST CONTROL CHECKOUT SYMPTOMS CHECKS YES/NO ACTIONS 1. LED off. 1. 24V R-B & Y-B at board, with unit running? N Repair low voltage wiring. Y Complete Check #2. 2.Short FRC_DFT pin to TEST_COMMON pin. Is defrost cycle initiated? N Replace defrost control. Y LED is bad but control will still function. 2. LED flashing very rapidly (greater than 4 times/sec) or appears to be on continuously. TEST_COMMON pin shorted to TST pin? Y Remove short. N Replace defrost control. 3. Control does not initiate a normal defrost. OD Temp. below 49°F. OD Coil temp. below 35°F.? "Delta" T increasing? N Check refrigerant circuits for balanced distribution of refrigerant if OD coil is frosting and delta T is not increasing 1. LED flashing? N Refer to SYMPTOM #1. Y Complete Check #2. 2. Check for 24V Y-B at board with unit running. N Repair low voltage wiring. Y Complete Check #3. 3. Check sensors for correct mounting (connection) and resistance. Remount or replace sensor if necessary. 4. Short FRC_DFT pin to TEST_COMMON pin. Is defrost cycle initiated? N Replace defrost control. Y Y-B signal or control may be intermittent 4. Control does not initiate a forced defrost. 24V R-B & Y-B at board with unit running? N Repair low voltage wiring. ...

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