Temp. Control Problem Diagnosis: Notes

In diagnosing a temperature control problem, it is important to separate refrigeration and heating problems from temperature control problems. If the complaint is no cooling or heating and the programmer moves to both extremes of travel with the air mix door, the problem is more likely in the refrigeration or heating system. Refer to appropriate Manual Systems (Heaters or Heater-Air Conditioner) article in this supplement for complete diagnosis procedures.

The following items may aid in determining area of temperature control problem, as many such problems result from poor electrical or vacuum connections:

1. A disconnected sensor or temperature dial interrupts electrical signal and drives programmer to maximum heating.
2. A poor sensor connection adds resistance to sensor string, driving system hotter.
3. An open amplifier power feed eliminates output signal and drives programmer to maximum A/C.
4. A disconnected vacuum hose supplying vacuum checking relay actuating nipple will lock relay in an intermediate position.
5. A disconnected vacuum hose in transducer-programmer vacuum motor line will drive system to maximum cooling.
6. A leak in auxiliary vacuum circuit may reduce transducer vacuum supply level below control requirements, causing an "off-calibration" or "poor heating" type complaint.
7. A loss of supply vacuum usually results in cold air flow on the floor.