GMC 1976 ZEO 6083 Maintenance Manual page 746

Figure 1 1-Time Delay Relay Check (Duo-Therm Only)
ROOF MOUNTED AIR CONDITIONER 24E- 7
Problem Remedy
3 . Circuit breaker box.
3. If there is no voltage to the compressor, check
the circuit breaker box. Be sure there is power to
the circuit, then check the circuit back to the
power source to find out where it's open . Make
these checks with a voltmeter negative (black)
probe at any common (white) wire terminal, and the
positive (red) probe at the terminal being tested .
a. Overload switch or circuit
a. Check for power to and from the overload .
breaker
If there is no power from the overload, but power
is okay to the overload, the overload is open .
Wait 15 minutes for the overload to cool . If it
doesn't reset, replace it .
b. Time delay relay
b. If the time delay relay has power in, there
(figure 11).
should be power out within three minutes. Close
the contacts with a stick of wood or insulated
handle screwdriver. Hold them closed long enough
for the compressor to start. If the compressor
starts and stays running after you release the
contacts, replace the relay.