System Performance Test

Fig. 1 Refrigerant Pressure & Temperature Charts. 190E:

Fig. 2 Refrigerant Pressure & Temperature Charts. 260E, 300CE, E, SD, SL & TE, 400E & SE, 500E, SEL & SL, 600SEL & 1992 300SE:

Fig. 3 Refrigerant Pressure & Temperature Charts. 300D:

Fig. 4 Refrigerant Pressure & Temperature Charts. 420SEC & 560SEC & SEL:

1. Do not allow vehicle to be exposed to sun before or during testing.
2. Ensure proper belt tension.
3. Check A/C fluid level as follows:
a. Remove pressure switch electrical connector.
b. Start engine and allow to idle, then position automatic climate control On using the up and down function key.
c. Clean sight glass on fluid reservoir.
d. While watching sight glass reconnect pressure switch electrical connector.
e. Before electromagnetic coupling is switched On, refrigerant should rise and then flow until refrigerant is not visible.
f. If system is empty or has refrigerant loss, pressure switch interrupts compressor voltage, then circuit is closed once pressure rises.
4. Check high and low line pressure as follows:
a. Remove high and low pressure line service caps.
b. Connect pressure gauges to service valves.
c. Open vehicle windows and close doors.
d. On 4 cylinder models, disconnect 100/110°C temperature switch electrical connector, then using suitable jumper wire, allow fan to run during test.
e. On all models, apply parking brake, start engine and allow to run at least ten minutes.
f. Read gauges, refer to Figs. 1 through 4, for specifications.
g. If suction pressure is too low and high pressure is too high a faulty expansion valve or clogged fluid reservoir, condenser or evaporator may be indicated.
h. If suction pressure is too high and high pressure is too low, a faulty expansion valve is indicated.
i. If suction and high pressure are the same, a faulty compressor is indicated.