GMC 1976 ZEO 6083 Maintenance Manual page 748

ROOF MOUNTED AIR CONDITIONER 24E- 9
COMPRESSOR STARTS, THEN CUTS OUT
COMPRESSOR IS OKAY, CHECK CAPACITORS AND RELAY
Problem Remedy
1 . Campsite power.
1 . One frequent cause is not enough power at the
campsite due to inadequate wiring or power avail-
ability. The air conditioner is designed to use
No . 12 gauge A/C wire cord . The campsite power
supply should be 120-volt AC .
2. Vehicle overloading. 2. The air conditioner may cut out when other ap-
pliances are operated on the 120-volt vehicle sys-
tem due to overloading.
3. Compressor winding 3. Turn power off and disconnect the compressor
continuity . leads. Use ohmmeter to check start winding conti-
nuity between the O and S terminals; run winding
continuity between the O and the M or R terminal ;
then check for continuity between the two winding
terminals. If there is an open circuit in any of
the checks replace the compressor .
4. Grounded compressor
4. Connect the ohmmeter between one of the copper
windings .
tubes and each of the winding terminals . There
should be an open circuit in each case. If not the
winding is rounded replace the compressor.
5. Shorted compressor 5. Use a precision ohmmeter with a 0-to-5 and
windings . 0-to-25 ohm scale. Check each winding resistance
and combined resistance against specifications .
Low resistance indicates a shorted winding and the
compressor should be replaced .
6. Motor generator.
6. If the unit works when connected to an external
power source but not from the generator the prob-
lem may be poor motor generator maintenance.
Check
the generator voltage. The motor generator must be
set to 60 cycles plus or minus one. Check with a
cycle meter (J-24673). The generator may cut out
due to an excess current draw caused by high head
pressure . This condition can be created by a high
heat load when the vehicle has been in the hot sun
all day. The return air to the evaporator may be
as high as 150°F (65 .6°C .) and the compressor
will cut out until it cools.
7. Compressor draw . 7. Put a snap-around amprobe around the power
wire . It should read about 16 amps with the com-
pressor running. Too much draw steadily, can indi-
cate an overcharge of refrigerant or a shorted
winding. A low draw can indicate an undercharge.
Problem Remedy
1 . Capacitors .
1 . With the power off connect the self-powered
test light (J-21008) to the capacitor terminals.
If the capacitor has an identified terminal, the