By Arlen Mauland
Vehicles:
1993 Chrysler, Dodge or Plymouth Minivan.
Engine:
2.5L, 3.0L, 3.3L
System:
Body/Chassis/Electrical.
Symptom/Problem:
A/C compressor clutch is inoperative except when the fan comes on for engine temperature.
The A/C compressor clutch is not being energized unless the radiator high speed fan turns on to cool the engine. It would seem obvious that an electrical problem is causing this. What is not as obvious is that the A/C clutch relay does not appear to be connected to the high speed fan relays. Let's take a closer look at the control of the radiator fan and the A/C compressor clutch.
The two-speed radiator fan motor has two sets of windings. The two windings are interconnected near the center of the windings within the fan motor, which is an important feature to remember. The low speed winding is permanently grounded on the black wire and the high speed winding ground is controlled through the yellow wire. The yellow wire goes to a relay that is energized at the same time the high speed fan relay is energized by the PCM.
The low speed fan relay is on the left fender side shield and has four wires. The gray wire supplies 12v to one of the relay's contacts at all times. The dark blue wire supplies 12v to the relay's winding when the ignition switch is in the "on" position. The dark blue with pink tracer wire is grounded by the PCM when the low speed fan is desired. When the relay is energized, the relay contacts close and 12v is supplied to the dark green wire to the fan motor and to the A/C clutch relay winding. This means that the radiator fan should run on low speed before the A/C clutch is able to energize.
The high speed fan relay is also on the left fender side shield and has five wires. The gray wire supplies 12v to one of the relay's contacts at all times. The dark blue wire supplies 12v to the relay's winding when the ignition switch is in the "on" position. It has two yellow wires that control the ground side of the relay's winding. One wire goes to the PCM and the other goes to the high speed fan relay and then to the radiator fan switch found on the A/C high pressure line near the condensor. When the yellow wire is grounded by either, the relay contacts close and deliver 12v to the light green wire that goes to the high speed fan motor winding. The high speed fan will not run until a ground is provided by the high speed fan ground relay.
The high speed fan ground relay is on the right fender side shield near the firewall. It also has five wires. The black wire is always grounded. The dark blue wire supplies 12v to the relay winding when the key is in the "on" position. It has three yellow wires. One terminal has two yellow wires and one terminal has one yellow wire. The terminal with two yellow wires is the relay's winding controlled ground. One wire goes to the radiator fan switch and the other comes from the high speed fan relay mentioned above. When either of these yellow wires is grounded, the relay contacts close and provide a path to ground for the terminal with one yellow wire that comes from the high speed fan motor winding.
The fourth relay involved is the A/C clutch relay found on the right fender near the high speed fan ground relay. This relay has four wires. The gray wire provides 12v to the relay at all times. The dark green wire is supplied 12v whenever the low speed fan relay is energized. The dark blue with orange tracer wire is grounded by the PCM when A/C is selected and the relay's contacts close, and supplies 12v to the dark blue with black tracer wire that goes to the compressor clutch.
The problem develops when the low speed fan relay's contacts will not close, and does not supply 12v to the dark green wire to the low speed fan motor winding and to the A/C clutch relay winding. This means that the A/C clutch relay cannot be energized even when the PCM supplies a ground on the dark blue and orange wire. If the engine runs hot enough so that the PCM will energize the high speed fan relay, a voltage potential will be supplied through the interconnected windings of the fan motor to the dark green wire. This will then allow the A/C clutch relay to energize as long as the high speed fan is running.
To diagnose, check the voltage on the dark green wire at the low speed fan relay when the A/C is selected. If it has more than 6v only when the high speed fan comes on, check the operation of the low speed fan relay.
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Arlen Mauland is an IDENTIFIX DaimlerChrysler, Mitsubishi and Hyundai specialist. He is ASE master and L1 certified.
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