Without CRT/DID

CIRCUIT DESCRIPTION
When the ECCP communications are lost. service diagnostics usually cannot be entered but a quick scan of the panel will usually help isolate the source of the fault. The ECCP is powered by ignition. If the power source is lost the IPC will usually display a "Electrical Problem" Loss of serial data will result in three dashes being shown on the panel VF display. This indicates power and ground are OK. If the panel displays normal outside or interior set temperature. power. ground. and serial communications are being received thus panel replacement is indicated.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This step checks for power and ground to the panel Test light should be "ON" for both power to ground checks.
2. Step checks for serial data voltage. Normal voltage should be above 1 volt and varying.