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A/C Clutch and Coil Problem

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This topic contains 19 replies, has 3 voices, and was last updated by Avatar Mark Stephen Lammers 5 years ago.

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  • #667465

    I replaced the compressor and clutch with a used assembly on my 2001 PT Cruiser. I bench tested the coil with a OHM meter and was around 5 Ohms. 2-5 is a good coil. Hooked up 12 volts to the clutch and coil and the clutch pulled in just fine. Put compressor /clutch assembly back in car and clutch would not engage with the ac switch. Checked OHMs on the coil and it was close to .4 OHMs. Bad Coils. Applied 12 volts straight to the clutch coil and still nothing happened other than wires getting hot because of a short. Could it be a fluke that the clutch coil went bad or is something in the wiring caused it.? All my wiring checks out fine with the wiring diagram. Checked for continuity and power to connectors and nothing is bad.

    I do have a question that is puzzling to me. In the line from AC relay to the Clutch coil, there is a diode. Symbol shows a Transient Voltage Suppression diode. I know what a regular diode is for but I have no idea what this diode does. Could this be a problem why it went bad? I’d hate to get another clutch and it burn up also.

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  • #667474
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    Andrew Phillips
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    The TVSD is designed to protect the clutch from electrical system weirdness (usually overvoltage) by shunting the circuit to ground. Just to clarify, when you re-checked the ohms on the clutch, it was disconnected, just like on your bench test?

    It’s possible the TVSD has failed, but that’s rare unless there was an electrical system problem (sometimes a faulty alternator can destroy the TVSD).

    #667487

    [quote=”cap269″ post=140253]The TVSD is designed to protect the clutch from electrical system weirdness (usually overvoltage) by shunting the circuit to ground. Just to clarify, when you re-checked the ohms on the clutch, it was disconnected, just like on your bench test?

    It’s possible the TVSD has failed, but that’s rare unless there was an electrical system problem (sometimes a faulty alternator can destroy the TVSD).[/quote]

    I did re-checked the ohms on the clutch on the car, it was disconnected, just like on your bench test. Used a multi-meter and got .4 Ohms (2-5 is good). Originally, on the bench it had 5 Ohms. Also applied voltage to the two leads at the connector to see if it would engage.

    #667638

    Just went to Pull a Part and bought another A/C compressor with clutch. Bench tested the coil and got 4 ohms. This should be good according to specifications. I applied 12 volts to the coil and did not get the clutch to engage. Now the coil reads .2 ohms. Now bad. Is it bad now from creating a load to the used coil? Is there a diode in the ac clutch coil in a 2001 2.4L PT Cruiser? Would the coil short out if you place a 12 volt positive source to the negative line of the coil and a the negative source line to positive of the coil?

    This is really getting frustrating.

    #667641
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    Andrew Phillips
    Participant

    The clutch coil is an electromagnet. It doesn’t matter which way polarity is hooked up.

    I have an idea the the bench testing is what is killing the clutch. I’ll bet you didn’t re-check the resistance after you put voltage to it. The diode in the diagram may be there to limit the amount of current flowing through the clutch, so without that, the clutch pulls an unrestricted amount of current and the coil wire melts, shorting it out.

    #667657

    [quote=”cap269″ post=140417]The clutch coil is an electromagnet. It doesn’t matter which way polarity is hooked up.

    I have an idea the the bench testing is what is killing the clutch. I’ll bet you didn’t re-check the resistance after you put voltage to it. The diode in the diagram may be there to limit the amount of current flowing through the clutch, so without that, the clutch pulls an unrestricted amount of current and the coil wire melts, shorting it out.[/quote]

    Good to hear that polarity doesn’t matter. So I didn’t burn it up from switching positive and negative voltage leads. Here is what I did exactly. Compressor and Clutch out of vehicle disconnected. I measured the Ohms at .4 before voltage testing the clutch. Battery I used had close to 12 volts. Hooked up positive to one line in connector and negative to other line. Rechecked resistance after putting voltage to coil and it measures .5 ohms. Bad coil.

    First compressor and clutch I tested, clutch engaged perfectly with voltage supplied. I put this compressor completely back into the vehicle and turned the ac switch to air. Nothing happened. Disconnected connector at the and measured resistance, which was .3 ohms. Could it be possible that both used coils were weak and could take the 12 volts?

    Therefore this is a big puzzle to me. So I’m burning up the coil in the vehicle and also on the work bench.

    #668160

    I do not have any power to Low Pressure Switch (DB/OR wire at pin #2}. Best I can guess is it coming from Blower wiring diagram? Am I wrong?

    #668178
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    Andrew Phillips
    Participant

    The DB/OR wire is a switched ground, not a power feed. 12v should be on the LG/BK wire. The computer switches the DB/OR to ground when, and only when, all the programmed conditions for safe operation have been met (pressures ok, ambient air temp ok, evap core temp ok, blower on, radiator (condenser) fan running, etc.)

    EDIT: I misunderstood which DB/OR wire. I see the other one now, at the pressure switch. This is also a switched ground, controlled by the mode switch. Notice how it connects to the same ground as the blower motor (trace the lines on the diagram back to the G203, and S200 for the motor). The only 12v going to that control unit appears to be for the illumination.

    #668222

    [quote=”cap269″ post=140951]The DB/OR wire is a switched ground, not a power feed. 12v should be on the LG/BK wire. The computer switches the DB/OR to ground when, and only when, all the programmed conditions for safe operation have been met (pressures ok, ambient air temp ok, evap core temp ok, blower on, radiator (condenser) fan running, etc.)

    EDIT: I misunderstood which DB/OR wire. I see the other one now, at the pressure switch. This is also a switched ground, controlled by the mode switch. Notice how it connects to the same ground as the blower motor (trace the lines on the diagram back to the G203, and S200 for the motor). The only 12v going to that control unit appears to be for the illumination.[/quote]

    So you are saying, G203 of the Blower diagram is the connected switched ground that the “AC Switch Sense” (AC wiring diagram top left corner)? Is the “AC Switch Sense” (AC wiring diagram bottom left corner) a ground also and derived from 12 volt parameters? I’m looking at the basic ac wiring diagram.

    I didn’t know that circuits could be switch grounded. After doing a little research, I see how is works. I found a basic ac wiring diagram. Actually, it was a you tube learning video.

    So you are saying that many things (pressures ok, ambient air temp ok, evap core temp ok, blower on, radiator (condenser) fan running, etc.) have to be met before the coil to the relay is energized, therefore pulling in the switch to the coil? The wiring diagram I have of my 2001 PT Cruiser is just a stripped down version of what other parameters of the program have to be met? How does someone find what other component parameters have to be met? Basically for testing.

    I do know one thing. The fan to the radiator is not coming on. I’m a little perplexed. What do you suggest checking in the PT Cruiser wiring diagram first?

    #668232
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    Andrew Phillips
    Participant

    [quote=”lmarkie” post=140995]So you are saying, G203 of the Blower diagram is the connected switched ground that the “AC Switch Sense” (AC wiring diagram top left corner)? [/quote]
    No, G203 is not a switched ground, it is the ground “source” (always a continuous ground).The switching is done by the knobs on the dash.

    Is the “AC Switch Sense” (AC wiring diagram bottom left corner) a ground also and derived from 12 volt parameters? I’m looking at the basic ac wiring diagram.

    No, the AC Switch Sense is a computer input (also a ground, and has nothing to do with +12v). When the AC is selected on the dash, this wire becomes grounded. This “pulls down” a transistor inside the computer. The computer is programmed to recognized the state of this transistor as knowing the on-off status of the A/C selection. The computer looks at the other parameters it is programmed for, and if all conditions are met, it then activates the output that switches on the compressor relay. Inputs, outputs, pull-ups, and pull-downs are essentially how computers operate.

    I didn’t know that circuits could be switch grounded.

    Ground-side switching is probably the most common type of switching you will find in modern cars. It is safer than voltage-side-switching, as short circuits become less hazardous. A ground shorting to ground doesn’t blow fuses and cause fires. Voltage shorting to ground does. In automotive circuits you will often find the 12v is fused and wired directly to the component while the switching occurs on the ground. This switching can be manually controlled through mechanical means or knobs/buttons on the dash, or digitally controlled by the computer.

    So you are saying that many things (pressures ok, ambient air temp ok, evap core temp ok, blower on, radiator (condenser) fan running, etc.) have to be met before the coil to the relay is energized, therefore pulling in the switch to the coil?

    Correct. The actual number of devices and programmed conditions varies from one vehicle to another, but the idea is the same. There are conditions that must be met. When those conditions are met, the system operates. If the conditions are not met, the system won’t. This is to protect expensive parts like the compressor. These system controls are in place to shutdown or prevent operation in order to protect them. A complete circuit diagram of just the A/C system, rather than a general diagram of the whole vehicle, will show all the various components involved. Once you are familiar with reading and interpreting wiring diagrams then it becomes fairly obvious which components are used as controls (generally any time a component is connected to a computer or a control module, especially if connected to a port with ‘sense’ in its name).

    I do know one thing. The fan to the radiator is not coming on.

    This could be the part of your problem. Does the fan not come on at all, even when the engine is warmed up? That needs to be repaired first, as engine damage could result from overheating.

    #668234

    I do know one thing. The fan to the radiator is not coming on.

    This could be the part of your problem. Does the fan not come on at all, even when the engine is warmed up? That needs to be repaired first, as engine damage could result from overheating.[/quote]

    When the engine heats up to operating temperature, the radiator fan does come on. Works fine keeping temperature down on engine. The low speed fan does not come on. Guess all the parameters and components have to be made for the fan to come on?

    #668238
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    Andrew Phillips
    Participant

    There are two relays for the fan. A low-speed and a high-speed. Make sure the low-speed relay is good. The low speed fan should come on before the high-speed fan when the engine is warm. If the relay is good, and jumping the load side of the relay (pins 25 and 26) does not cause the fan to come on, the fan motor has an internal fault or a wiring fault on the dark green wire.

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    #668240

    I bought a almost new radiator fan yesterday on craigslist. Couldn’t resist, $25. I’m going to change it out. Maybe an hour at the most. Then I’ll check out the low speed relay on 85 and 86 pull in, and see if it jumps 30 to 87.

    #668257

    [quote=”lmarkie” post=141013]I bought a almost new radiator fan yesterday on craigslist. Couldn’t resist, $25. I’m going to change it out. Maybe an hour at the most. Then I’ll check out the low speed relay on 85 and 86 pull in, and see if it jumps 30 to 87.[/quote]

    Switched the new radiator fan. With the old fan turned didn’t turn on with AC switched on and turned on when engine reached operating temperature.

    Now the new one doesn’t turn on at all. Will not turn on with AC switched and when engine reaches operating temperature. Had to turn engine off before it over heated. I can jump 30 and 87 on the relay connector and it will work. 85 is switched power and bridges to 86, so this tells me that 86 is connecting to ground through the PCM. Same for High Pressure Relay.

    Very frustrating and disappointing.

    Edit: When I jumped 30 and 87 got a P1490 Code. Says over 10v detected should be 30-70 ohms. I bench test the relay with energizing the 85 and 86 terminal and measure 0 ohms across 30 and 87. That’s how you get low speed. From the relay reducing the 12v?

    #668264
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    Andrew Phillips
    Participant

    The relay is a magnetic switch. The electromagnet’s coil gets 12v (fused) on pin 85 and switched ground on pin 86 (sometimes the use of pins 85 and 86 is reversed, depending on manufacturer). When the electromagnet is energized, the contacts close and form an electrical connection between pins 30 and 87. For relays with 3 load side terminals, there is pin 30 (common), 87 (normally open contact), and 87a (normally closed contact). In that case, when the relay is not energized (off), the contacts 30 and 87a are closed together and 87 is open. When the relay is energized, it reverses, and 30 and 87 are closed together and 87a is open. For the fan circuit, the fused 12v is run directly to pin 30 on the relay, the fan motor is connected to 87, and 87a is not used. With the relay removed, there should be 12v on pin 30 in the socket. There should also be 12v on pin 85 (or 86, depending as stated above) when the key is on. If there is no voltage there then the fuse is bad or there is a wiring fault.

    To get the high and low speeds, there is a dropping resistor inside the fan motor. When the low speed relay is activated, the voltage is sent through the resistor, dropping it to around 9-10v, and on to the motor windings. When the high speed relay is activated, this dropping resistor is bypassed internally in the fan so that full voltage gets to the motor windings. It is common on these fans for this resistor to burn out, which is why they work on high speed but not on low speed.

    There are three wires on the fan. A black, a dark green, and a yellow. If you apply 12v to the green wire with the black wire grounded, the fan should run on low speed. If it does not, the dropping resistor or fan motor is bad. Likewise, if you apply 12v to the yellow wire with the black wire grounded, the fan should run at full speed. It not, the fan motor is bad. If the fan works on both low and high speed with the direct voltage test, but not when connected normally, then the relays or fuse is bad, or there is a wiring fault.

    #668288

    Testing the fan with ground in the middle of the connector and connecting a positive lead on the left side blue wire and right side blue wire, doesn’t sound like the fan speeds are any different to me. So I must have a bad resistor in the new fan.

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