Carrier 90MA/MF/MU manual Service

switch T-HIGH to energize liquid line solenoid (LLS) [to activate the full evaporator coil and all compressor cylinders]. If thermostat switch T-HIGH is not calling for cooling, power flows to energize compressor unloader solenoid (US) [to unload compressor cylinders].

When room temperature falls to the cutout point of T-LOW, switch T-LOW opens to de-energize CHR, stopping the compressor motor and energizing CH. The machine enters a stand-by state, ready to restart automatically on room thermostat call for cooling.

If any safety device opens (CLO, SPS, DPS, IP, OLA or, OLB) relay CHR is de-energized, stopping the compressor motor and energizing the crankcase heater.

TO PLACE THE UNIT IN THE HEAT MODE: The switch (SW) is placed in the HEAT position. With thermostat (T-LOW) calling for heating (closed to contacts R & B), 24 volt control power flows through manual reset temperature cutout MC to energize safety relay H2. Power also flows through air flow switch (AS) and automatic cutout (AC) to energize operating relay (H1). Energizing relays H1 and H2 closes contacts to energize the heaters.

Placing SW in the FAN position de-energizes all cooling or heating control circuits in the same manner as activation of a safety switch. Placing SW in the OFF position also de-energizes IFC to stop the indoor fan motor.

5.SERVICE

WARNING

Never reach into unit while fan is running. Lock open and tag unit disconnect before working on fan. Remove fuses and take them with you after noting this on tag.

CAUTION

Sharp edges of coil fins are exposed. To pre- vent injury, cover top of evaporator with cardboard or a few layers of heavy tape.

CAUTION

To avoid coil damage, cover evaporator face with plywood or other rigid sheet material. If any coil fins are mashed or bent, straight- en with a coil fin comb of the proper tooth spacing (refer to “coil fins/inch” in Table 1 through Table 2). Check for refrigerant leaks.

5.1Return--Air Grille Removal a. Pull grille out from top.

b. Pull grille up to release hinge pins from lower panel. c. To reassemble, reverse procedure.

5.2Access Panel Removal

a.Remove return-air grille as described above.

b.Remove the panel fastening screws now exposed.

c.Pull out and down to remove top panel.

d.Pull out and up to remove bottom panel.

5.3Evaporator Fan Adjustment

WARNING

Never reach into unit while fan is running. Lock open and tag unit disconnect before working on fan. Remove fuses and take them with you after noting this on tag.

SPEED ADJUSTMENT - The fan motor pulleys are factory set at the fan speeds listed in Table 1, Table 3 or Table 2. to change fan speed, do the following:

a. Shut off unit power supply.

b. Loosen fan belt by loosening fan motor from mount- ing bracket. Do not loosen fan motor mounting brack- et from unit.

c. Loosen movable pulley flange set screw (Figure 8).

d.Screw movable flange toward fixed flange to increase fan speed and away from fixed flange to decrease speed. Increasing fan speed increases load on motor. Do not exceed maximum allowable fan speed or mo- tor full load amps indicated on motor nameplate.

e.Set movable flange set screw at nearest flat of pulley hub and tighten set screw.

f.Check pulley alignment and belt tension adjustment as described below.

g.Check fan operation. Repeat above procedure as re- quired.

Figure 8 Fan Pulley Adjustment

PULLEY ALIGNMENT - Shut off unit power supply. Loosen fan motor pulley set screws and slide fan pulley along fan shaft. Make angular alignment by loosening motor from mounting bracket (See Figure 8).

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