Intermittent AC
#1
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Join Date: Nov 2011
Location: Coarsegold, CA
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Year: 1998
Model: Cherokee
Engine: 4.0
Intermittent AC
When I was driving this afternoon, AC blew hot air.. When I check it in my garage in my garage there is plenty of refrigerant and the AC blew cold. Any ideas why it would be intermittent?
#2
Senior Member
Hook up a set of r134a manifold gauges and see what the pressures are. There's also a high and low pressure switch that will prevent it from energizing the compressor clutch, and the clutch itself could be the problem. But start with the pressure first.
#3
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Join Date: Nov 2011
Location: Coarsegold, CA
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Year: 1998
Model: Cherokee
Engine: 4.0
Am I going about this the wrong way?
#4
Senior Member
If there is sufficient static pressure that you know there is at least enough refrigerant so the compressor won't be damaged, try bridging the contacts in the low pressure switch connector with a paperclip and see if the compressor engages. If it does then your low pressure cutoff switch is defective. (Keep an eye on pressures. You don't want the compressor running with the low side below about 20 psi, which is when the low pressure cutoff would kick in.)
This is the low pressure test procedure in the 1999 service manual:
This is the low pressure test procedure in the 1999 service manual:
LOW PRESSURE CYCLING CLUTCH SWITCH
Before performing diagnosis of the low pressure
cycling clutch switch, be certain that the switch is
properly installed on the accumulator fitting. If the
switch is too loose it may not open the Schrader-type
valve in the accumulator fitting, which will prevent
the switch from correctly monitoring the refrigerant
system pressure. Remember that lower ambient tem-
peratures, below about -1° C (30° F), during cold
weather will open the switch contacts and prevent
compressor operation due to the pressure/tempera-
ture relationship of the refrigerant.
Also verify that the refrigerant system has the cor-
rect refrigerant charge. See Refrigerant System
Charge in the Service Procedures section of this
group for more information.
For circuit descriptions and diagrams, refer to
8W-42 - Air Conditioning/Heater in Group 8W - Wir-
ing Diagrams.
(1) Disconnect and isolate the battery negative cable.
(2) Unplug the low pressure cycling clutch switch
wire harness connector from the switch on the accu-
mulator fitting.
(3) Install a jumper wire between the two cavities
of the low pressure cycling clutch switch wire har-
ness connector.
(4) Connect a manifold gauge set to the refrigerant
system service ports. See Refrigerant System Service
Equipment and Refrigerant System Service Ports in
the Description and Operation section of this group
for more information.
(5) Connect the battery negative cable.
(6) Place the heater-A/C mode control switch ****
in any A/C position and start the engine.
(7) Check for continuity between the two terminals of
the low pressure cycling clutch switch. There should be
continuity with a suction pressure reading of 262 kPa
(38 psi) or above, and no continuity with a suction pres-
sure reading of 141 kPa (20.5 psi) or below. If OK, test
and repair the A/C switch sense circuit as required. If
not OK, replace the faulty switch.
Before performing diagnosis of the low pressure
cycling clutch switch, be certain that the switch is
properly installed on the accumulator fitting. If the
switch is too loose it may not open the Schrader-type
valve in the accumulator fitting, which will prevent
the switch from correctly monitoring the refrigerant
system pressure. Remember that lower ambient tem-
peratures, below about -1° C (30° F), during cold
weather will open the switch contacts and prevent
compressor operation due to the pressure/tempera-
ture relationship of the refrigerant.
Also verify that the refrigerant system has the cor-
rect refrigerant charge. See Refrigerant System
Charge in the Service Procedures section of this
group for more information.
For circuit descriptions and diagrams, refer to
8W-42 - Air Conditioning/Heater in Group 8W - Wir-
ing Diagrams.
(1) Disconnect and isolate the battery negative cable.
(2) Unplug the low pressure cycling clutch switch
wire harness connector from the switch on the accu-
mulator fitting.
(3) Install a jumper wire between the two cavities
of the low pressure cycling clutch switch wire har-
ness connector.
(4) Connect a manifold gauge set to the refrigerant
system service ports. See Refrigerant System Service
Equipment and Refrigerant System Service Ports in
the Description and Operation section of this group
for more information.
(5) Connect the battery negative cable.
(6) Place the heater-A/C mode control switch ****
in any A/C position and start the engine.
(7) Check for continuity between the two terminals of
the low pressure cycling clutch switch. There should be
continuity with a suction pressure reading of 262 kPa
(38 psi) or above, and no continuity with a suction pres-
sure reading of 141 kPa (20.5 psi) or below. If OK, test
and repair the A/C switch sense circuit as required. If
not OK, replace the faulty switch.
#6
CF Veteran
generally when this happens the system is slightly low and the evap coil temps are too low and make the water in the air condense and freeze. Then the air gets blocked in the coil and you blow hot air. Turn it off and the ice melts and the air will blow cold again
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