Table 4-3. Normal Operating Pressures and Currents.

Table 4-3. Normal Operating Pressures and Currents.

Outdoor Ambient

95 F

120 F

FDb

Temperature-

(35 C)

( 4 8 . 9 C)

90FDb

R e t u r n Air to

(26.7 F)

( 3 2 . 2 C)

75 F Wb

67 F Wb

Unit-

FDb

and

(19 C)

(24 C)

Gage Pressure

60-70

75-90

Suction-PSIG

260-270

360-380

Discharge-PSIG

14-16

18-20

Current-Amperes

Note: Db (Dry bulb)

Wb (Wet bulb)

required for the suction strainer. The only in-

4-59. Solenoid Valves

spection being, checking for refrigerant leaks

T w o solenoid valves are used in the air conditioner.

particularly at the inlet and outlet suction line

B o t h are normally open valves. L1 (fig. 1-6) is the

c o n n e c t i o n s (para 4-55). A clogged suction strainer

liquid line solenoid valve. It is controlled by the

would result in excessively low suction pressure

thermostat setting. W h e n e v e r t h e i n t a k e a i r

(para 4-58). Severe clogging of the strainer could be

temperature reaches the setting of the thermostat

e v i d e n c e d by frost forming on the exterior surfaces.

t h e electrical circuit to the L1 solenoid is energized

thus closing the valve to stop the flow of refrigerant

4-62.

Thermostatic

Expansion

Valves

through the evaporator coil. When the temperature

a. General. Two thermostatic expansion valves

rises, the valve is de-energized and thus opens

a r e used in the air conditioner. One expansion valve

p e r m i t t i n g liquid refrigerant flow to the evaporator

controls the rate of flow of liquid refrigerant into

t o resume cooling. The L2 solenoid valve (fig. 1-6)

the evaporator coil during the cooling cycle of

i s the compressor by-pass solenoid and is piped in

operation. The second expansion valve functions

parallel with the compressor. When the compressor

w h e n the unit is in the by-pass cycle of operation.

stops the valve de-energizes and assumes its nor-

E a c h valve is equipped with a super heat setting or

mally open position thus allowing pressure to

adjustment, 10 F. for the main valve and 25 F.

equalize from the discharge to the suction side of

for the by-pass valve to assume efficiency in the

the compressor. To determine if L1 is functioning

refrigerant system. The adjustment procedures may

properly, observe the sight glass and if flow is

be applied to either or both expansion valves.

noted, valve is open. Adjust thermostat to the

Adjust only when absolutely necessary and then

higher setting and flow should stop. Check L2 by

only during the cooling cycle.

r e m o v i n g the top panel of the unit and feeling the

b. Adjustment.

l i n e out of the valve. If line is warm, valve is not

(1) Tape the bulb of a thermometer to the

closing when energized. Check coil of both valves

suction tube near the sensing element. Insulate the

f o r continuity and ground by using an ohmmeter. It

thermometer bulb.

s h o u l d r e a d a r e s i s t a n c e o f SO o h m s , a p -

(2) Install a suitable pressure gage at suction

proximately.

service valve.

4-60. Suction and Discharge Service Valves

(3) Operate the unit for approximately 30

minutes or until thermometer reading stabilizes.

T h e air conditioner is equipped with a suction and

(4) Check thermometer and pressure gage

a discharge service valve located behind an access

readings. Compare readings with figure 4-2.

p a n e l next to the CBR duct cover at the rear of the

Thermometer reading should be approximately

air conditioner. Test of the service valves consists of

1 0 F. for the valve feeding the evaporator coil and

c h e c k i n g to insure that they do not leak. (para. 4-

25 F. for the by-pass valve, higher than the

5 5 ) . Be sure that the caps are securely fastened to

saturated refrigerant temperature.

the service valve-openings.

(5) Remove cap from side of valve. If tem-

4-61 Suction Strainer

perature reading is high, turn adjusting screw

The suction strainer is an integral part of the

counter-clockwise approximately one turn for each

c o m p r e s s o r . It serves to prevent large contaminants

4 F. that temperature is high. If temperature

(particles measuring greater than 5 microns) from

reading is low turn adjusting screw clockwise

entering the compressor. Service is normally not

approximately one turn for each 4 F. that

4-19