Heater Performance; Maximum Heater Output; Obstructed Coolant Flow; Mechanical Problems - Jeep Wrangler 1997 Manual

TJ
DIAGNOSIS AND TESTING (Continued)
HEATER PERFORMANCE
PREPARATIONS
Review the Service Warnings and Precautions in
the front of this group before performing the follow-
ing procedures .
Check the radiator coolant level, serpentine drive
belt tension, and engine vacuum line connections .
Also check the radiator air flow and the radiator fan
operation . Start the engine and allow it to warm up
to normal operating temperature .
WARNING : DO NOT REMOVE
THE RADIATOR
PRESSURE CAP WHEN THE ENGINE IS AT OPER-
ATING TEMPERATURE, PERSONAL INJURY MAY
RESULT.
If the vehicle has been operated recently, wait 15
minutes or longer before removing the radiator pres-
sure cap . Place a rag over the cap and turn it to the
first safety stop. Allow any pressure to escape
through the overflow tube . When the system stabi-
lizes, remove the cap completely.
MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core
through two heater hoses . With the engine idling at
normal operating temperature, set the temperature
control knob in the full hot position, the mode control
switch knob in the Floor position, and the blower
motor switch knob in the highest speed position.
Using a test thermometer, check the air temperature
coming from the floor outlets, refer to the Tempera-
ture Reference Chart.
Minimum Heater System
Ambient Temperature
Floor Outlet Temperature
Celsius
Fahrenheit Celsius
Fahrenheit
15 .5° 60 0
62 .2 ° 144°
21 .1 0 70 0
63.8 ° 1470
26 .6 ° 80 0
65 .5 ° 150 0
32 .2 °
90o
67 .2 0
153 0
Temperature Reference Chart
9124-4
If the floor outlet air temperature is low, refer to
Group 7 - Cooling System for the coolant tempera-
ture specifications . Both of the heater hoses should
be hot to the touch. The coolant return hose should
be slightly cooler than the supply hose. If the coolant
return hose is much cooler than the supply hose,
locate and repair the engine coolant flow obstruction
in the heater system .
HEATING AND AIR CONDITIONING 24-11
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant
flow:
" Pinched or kinked heater hoses.
" Improper heater hose routing.
" Plugged heater hoses or supply and return ports
at the cooling system connections (refer to Group 7 -
Cooling System) .
" A plugged heater core.
If proper coolant flow through the heater system is
verified, and outlet air temperature is still low, a
mechanical problem may exist.
MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat :
" An obstructed cowl air intake.
" Obstructed heater system outlets .
" A blend-air door not functioning properly.
TEMPERATURE CONTROL
If the heater discharge air temperature cannot be
adjusted with the temperature control knob on the
heater-A/C control panel, the following could require
service :
" The heater-A/C control .
" The temperature control cable.
" The blend-air door.
" Improper engine coolant temperature .
VACUUM SYSTEM
Vacuum control is used to operate the mode doors
in the heater-A/C housing. Testing of the heater-A/C
mode control switch operation will determine if the
vacuum, and mechanical controls are functioning.
However, it is possible that a vacuum control system
that operates perfectly at engine idle (high engine
vacuum) may not function properly at high engine
speeds or loads (low engine vacuum) . This can be
caused by leaks in the vacuum system, or a faulty
vacuum check valve.
A vacuum system test will help to identify the
source of poor vacuum system performance, or vac-
uum system leaks. Before starting this test, stop the
engine and make certain that the problem isn't a dis-
connected vacuum supply tube at the engine intake
manifold vacuum tap or the vacuum reservoir.
Use an adjustable vacuum test set (Special Tool
C-3707) and a suitable vacuum pump to test the
heater-A/C vacuum control system . With a finger
placed over the end of the vacuum test hose probe
(Fig. 6), adjust the bleed valve on the test set gauge
to obtain a vacuum of exactly 27 kPa (8 in. Hg .).
Release and block the end of the probe several times
to verify that the vacuum reading returns to the
exact 27 kPa (8 in . Hg.) setting. Otherwise, a false
reading will be obtained during testing .