Automatic Temperature Control: Testing

Step	Tester Settings			Tester Should Indicate:	To Correct Abnormal Indication:
Step	Rocker Switch	Voltage	Manual Control	Tester Should Indicate:	To Correct Abnormal Indication:
1	Manual	Source	150	Battery Voltage	Check fuse and wiring.
2	Manual	Sensor	150	Battery Voltage	Check for open in sensor circuit.
3	Manual	Amplifier or Control Cal.	a. Max. Heat*	0-4 Volts	Malfunctioning Amplifier or Temperature Dial.
3	Manual	Amplifier or Control Cal.	b. Max. Cold*	8 Volts Min.	Malfunctioning Amplifier or Temperature Dial.
4	Manual	Transducer	a. Max. Cold*	8 Volts Min. 0-3 in. Vac.	Check for open or bad ground in transducer circuit. Check vacuum relay valve when voltage is correct but vacuum is incorrect in max. cold position.
4	Manual	Transducer	b. Max. Heat*	0-4 Volts 9 in. Min. Vac.
5A	Manual	Amplifier or Control Cal.	Set to 150 for Comfortron System	6.5 Volts	Rotate car temperature dial until meter reads 6.5 volts. Car temperature should indicate 75°. If not, see temperature calibration which follows.
5B	Automatic	Amplifier or Control Cal.	Same as 5A. Allow 5 min. for system to stabilize with doors and windows closed.	5.5 to 7.5 Volts	After 5 minutes of operation check for defective sensor.

Fig 1: Chevrolet Comfortron Electrical Diagram (With Indicated Test Points)

Courtesy of GENERAL MOTORS COMPANY

RESISTOR CHECK
Control Head Setting	Tester Settings			Tester Should Indicate:	If not, check the following:	Electrical Diagram Probe Points:	Voltmeter should read
Control Head Setting	Function	Manual Control	Voltage	Tester Should Indicate:	If not, check the following:	Electrical Diagram Probe Points:	Voltmeter should read
Lo Front	Manual	Rotate from Max. Heat to Max. Cold	Transducer	Complete series of blower changes from Hi to Lo to Hi again.	Resistor	14	Battery Voltage
Lo Front	Manual	Rotate from Max. Heat to Max. Cold	Transducer		Resistor	25-40-42-44-15	Minimum 6 volts
AMPLIFIER CHECK
Hi Front	Manual	150	Amplifier	Remove conn. from control head temperature dial. Voltage reading should be 9 volts minimum. Short this lead to ground. Voltage reading should be 0 volts. No voltage change indicates malfunctioning of amplifier.
COMPRESSOR CLUTCH CHECK
Hi Front	Manual	Max. Cold	Transducer	Cooling System Operation	Compressor Clutch (Grille Temp. must be above 40°.)	26-27-28	Battery Voltage
DE-ICE CIRCUIT
De-Ice 65° on Temp. Dial	Automatic	Max. Cold	Probe	Assuming rest of system is operating normally: Max. Heat to windshield.	Blower Switch	3-4	Battery Voltage
					Master Delay Relay	20-10-21	Battery Voltage
					Transducer	38	Zero Voltage
SENSOR STRING CHECK
Hi Front	Automatic	-	Probe	-	Sensor String	29-30	Battery Voltage
POWER SERVO FEEDBACK POTENTIOMETER CHECK
Hi Front	Manual	Rotate slowly from max. cold to max. heat and vice-versa	Transducer	Remove Power Servo 6-terminal connector and install ohmmeter at pink and yellow connections (points 32 and 33). Ohmmeter needle should move smoothly from approximately 70 ohms at max. cold to approximately 15 ohms at max. heat, or vice-versa. If an erratic movement is noted, the feedback potentiometer is defective.
TRANSDUCER CHECK
Hi Front	Manual	Max. Cold	Transducer	0-3" Vac. Reading 8 Volts Min.	Transducer voltage (at Max. Cold position)	37-38	Battery Voltage
		Max. Cold		0-3" Vac. Reading 8 Volts Min.	Transducer voltage (at Max. Cold position)	NOTE: If voltage is correct but vacuum is incorrect, check vacuum relay.
		Max. Heat		9" Min. Vac. Reading 0-4 Voltage Reading	Transducer Ground