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Failure to do so will constitute abuse. Equipment failure due to abuse is not covered by the Warranty To restart unit, push manual reset button in unit control box (except 38AB054 and 064 units). Reset button is on OPS on 38AB054 and 064. Compressor Motor Protection on 38AD024 thru 044 and 38AB084 consists of three temperature sensors (one for each phase) embedded in the motor windings, and solid state modules in unit control box. Sensors are part of a temperature bridge. If a motor winding overheats, the bridge circuit will unbalance and a silicone-controlled rectifier in the module will de-energize a relay which opens a set of normally open contacts in the module and stops the compressor. If one sensor fails, it can be jumped with a 75-ohm, 2-watt resistor. When checking or testing module, do not apply more than 6 volts across sensor terminals. Many test instruments exceed this voltage rating; check before using. If a component in a module fails on 38AD024 thru 044, the entire module must be replaced. On 38AB084, the transformer is external to the module and may be replaced separately. Replace transformer with a Carrier specified balanced transformer. To restart compressor after shutdown due to motor protection trip, push control circuit reset button in unit control box. Safety Relief — All 38AB,AD units are protected against excessive pressure by a fusible plug inserted in the liquid line. Winter Start Control — On 38AB units (not necessary on 38AD units because the timer supplies this function), install a liquid line pressure-stat (Carrier part no. HK02AB026) and evaporator freeze-up protector (defrost thermostat, Carrier part no. HH22UA025). 38AD control circuits incorporate a 150 seconds timed bypass of the low-pressure switch to 1П allow unit to start under low-ambient conditions. An evaporator freezestat must also be installed in series with the control thermostat(s) to prevent coil freeze-up (See lower part of Fig 15 — EDT Wiring section.) LIQUID LINE PRESSURESTAT - Connect to system liquid line service valve port. Connect switch into control circuit as shown on unit label -> diagram or in Fig. 15. Pressurestat is set to cutout at 5 psig with a differential of 10 psig. Do not change setting Fig. 15 — Unit Wiring Changes for Winter Start Control DEFROST THERMOSTAT - Position switch so that moisture cannot enter switch insulator. Install control with approximately 2 in. of top of thermostat capillary passing thru lower part of evaporator coil and with remainder of capillary inserted between fins on entering air side of coil. Connect thermostat electrical contacts into indoor cooling thermostat circuit or in series with compressor holding coil. Thermostat is set to cut out at 25 F and cut in at 55 F. Contact rating is 16 amps and 230 volts. As evaporator coil frosts, coil fin temperature drops to thermostat cutout setting, and stops compressor. Evaporator fans keep running to defrost coil with room air. As indoor coil defrosts, fin temperature will rise to thermostat cut-in setting. Compressor starts when cooling is required. NOTE. Use a defrost thermostat on all systems operating with outdoor temperatures below 45 F. Fan Adjustment — When replacing a fan, adjust fan until top surface of hub plate is below the top of the orifice ring as indicated in Fig. 16. Then, tighten both setscrews, located over the keyway of the fan hub of the motor shaft. Seal recessed area of fan hub bore with Permagum to prevent rusting. Lubrication FAN MOTORS have permanently lubricated bearings. No provisions for lubrication are made. COMPRESSOR has its own oil supply. Loss of oil due to a leak in the system should be the only reason for adding oil after the system has been in operation. To Add or Remove Compressor Oil 1. Stop compressor and close suction service valve. Pump down compressor to 2 psig. Stop compressor and close discharge shutoff valve. 2. Relieve crankcase pressure by disconnecting line, at compressor, which goes to low-pressure connection of oil safety switch. 3. Add oil thru oil filter connection. 4. Remove oil thru drain plug in bottom cover. Remove small amounts of oil thru oil discharge connection with compressor running. Fig. 16 — Fan Adjustment 11 I \ i For replacement items use Carrier Specified Parts. Manufacturer reserves the right to change any product specifications without notice. CARRIER AIR CONDITIONING COMPANY • SYRACUSE, NEW YORK Tab 4 Form 38AD-6S1 Supersedes 38AD-5SI Printed in U.S.A. 37 3 4-72 Codes B and MS Catalog No. 533-860...

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