Heater - Insufficient Heat
Article No.
87-6-8 HEATER - INSUFFICIENT HEAT
MERKUR 1985-87 XR4Ti
ISSUE: Some Merkur XR4Ti vehicles may experience one or more concerns affecting the heater system.
ACTION: This article outlines these concerns and applicable service actions. Because of the possibility of more than one concern cause on a complaint vehicle, technicians should consider all of the causes to assure proper operation of the total heat system.
NOTE: All 1985-86 and some early 1987 XR4Ti vehicles are equipped with a temperature gauge sending unit that, in cold weather, is slow to respond to a cold engine; and may cause the gauge to read in the lower end of the normal band when driving with a warm engine. The low gauge reading may lead some owners to believe the system is not producing maximum heat when in all probability it is. Refer to TSB 86-24-9 for this concern.
Engine Operating Temperature
In all cases relating to heater system concerns it is recommended that the vehicle be checked for normal engine operating temperature to assure proper repairs are performed. To do so, start with a cold engine and the coolant reservoir cap removed. Place a digital probe or dial-type thermometer in the reservoir and start the engine. When the temperature reading starts to rise, with a bare hand, feel the upper radiator hose a few inches back from the thermostat housing. The hose should remain cold until the temperature reading in the reservoir reaches approximately 165~F (74~C).
At this point the engine coolant at the thermostat will be 192~F (89~C), the thermostat should open and the radiator hose should rapidly become hot to the touch and then begin to cool slightly as the coolant flows through the radiator. Thereafter, with the engine RPM increased to 1500-1800, the hose heat can be felt alternately changing as the thermostat opens and closes.
If the temperature reading is very slow in rising and the upper radiator hose gradually warms at the same time (before the temperature in the coolant reservoir reaches 165~F, 74~C), the thermostat should be serviced before proceeding further. Refer to Group 27 of the Merkur XR4Ti Shop Manual for removal and testing procedures.
NOTE: Vehicles built prior to June 2, 1986 were equipped with a thermostat that may not have been properly seated in the housing during assembly of the engine. These thermostats may not fully close and often may stick fully open. Generally these vehicles will not reach normal operating temperatures and there will be insufficient heat, particularly when driving at highway speeds. This concern was corrected in production with a new design thermostat which is also released for service. The part number is E6FZ-8575-A (RT-1055).
Heater Control Servo Switch
All vehicles built prior to July 10, 1986 and subjected to high interior temperatures during summer months may have a servo switch that will stick in the cold position. This servo switch is attached to the heater/A/C temperature control lever in the control assembly and controls the vacuum supply to the heater water valve in the engine compartment. When the switch is stuck
there will be full vacuum to the water valve and as a result, cold air from the heater. To check the operation of this switch, place the temperature control in the full warm (red) position and disconnect the vacuum hose from the top of the water valve. With the hose disconnected there should be no vacuum at the hose and maximum heat from the heater. If vacuum is found at the hose the switch is not operating correctly. If the switch is not operating correctly, replace it with a new switch (E7RY-18C311-A). The switch can be accessed by removing the instrument panel cluster assembly. Refer to the Merkur XR4Ti Shop Manual, Section 33-50 for this procedure.
NOTE: Because the servo switch plunger is spring loaded, this concern is often intermittent in nature. It usually occurs when the temperature lever has been positioned to the lowest (blue) position and then moved up to the red area.
Heater Water Valve
To check the heater water valve, bring the engine to normal operating temperature. Place the temperature control lever in the full cold (lowest) position and activate the blower motor. The air flow from the heater should be cold. Place the temperature lever to full hot (highest) position. The air flow should now be maximum warm (approximately 140~F, 60~C, or higher). If the air is still cold or significantly below 140~F (60~C), remove the vacuum hose from the top of the water valve and recheck the air flow. If there is no change replace the water valve (E5RY-18495-A).
Heater Core
All vehicles built prior to May 19, 1986 were equipped with a normal duty heater core which may not produce adequate heat when outside temperatures are extremely low. Vehicles built after this date are equipped with a heavy duty core which increases the heat output by 12 to 15 degrees. Service part heater cores (E5RY-18476-A) were also upgraded at this time.
Temperature Guidelines
The following temperatures are measured at the center instrument panel register, outside air mode and on the number 2 blower position. Field readings will vary somewhat depending on the type of thermometer used and outside temperatures.
^ Idle - warm engine, 140~F (60~C).
^ Idle - hot engine, 150~F (65~C).
^ Highway speed - outside temperature 32~F (0~C), 152~F to 150~F (67~C to 65~C).
PART NUMBER PART NAME CLASS
E5RY-18476-A Heater Core C
E7RY-18C311-A Heater Servo Switch C
E5RY-18495-A Water Valve C
E6FZ-8575-A Thermostat C
(RT-1055)
OTHER APPLICABLE ARTICLES: 86-24-9
WARRANTY STATUS: Reimbursable within the provisions of the Warranty and Policy Manual
OPERATION: SP870608A - Check heater system*
TIME: 0.6 Hr. DLR. CODING: Basic Part No. 18476 - Code: 53
* Includes time to check engine operating temperature, operation of servo control switch, operation of water valve and road test.
Additional time as required:
OPERATION: SP870608B - Replace heater core
TIME: 2.1 Hrs.
OPERATION: SP870608C - Replace servo control switch
TIME: 0.5 Hr.
OPERATION: SP870608D - Replace water valve
TIME: 0.4 Hr.
OPERATION: SP870608E - Remove - test and install thermostat
TIME: 0.6 Hr.