Issue with power to Aircond clutch

[bigmal 225]

Hi all,

I have been trouble shooting my air-conditioning working intermittently. I put 12 volts to the clutch and it works. Checked power from the clutch wire and it was 11.5 volts with engine running but will only occasionally pull the clutch in. I the noted that the voltage is dependant on fan position  - 6.5, 9 and 11.5 volts. I have a Sandon compressor.

Questions:

Should the clutch work at lower voltages? 

Is the power to the clutch from the wrong source? Should it be always 12-14 volts?

I can't see how it would be wired differently. I have been thinking of adding a relay so that the relay will work with less voltage. Could be a simple fix.

Thoughts???

[barnett468 418]

midlife will know where the factory wire tied into, however, it needs 12 volts direct from the battery. there may be a threaded post on the back of your switch. if there is, you can use that then install a fuse like around 15 - 20 amps. You can also connect it to the lighter fuse or heater fan fuse on the fuse box.

there should always be 11 - 12 volts when the clutch is engaged. if there is not then something is wrong. for a test you can just temporarily connect it directly to the battery. if it shuts off then, the clutch or clutch pickup is likely bad unless you have pressure sensors in the system. if the freon gets too low, the sensor will shot the power off to the clutch.

 

 

[Midlife 814]

Power to the AC clutch goes through two switches under the dash before going out to the AC unit itself; those switches should not be dependent upon fan speed selection, which is controlled by the heater box resistor wire.  I believe someone has mis-wired your AC such that the output of the resistor complex is now hooked up to the AC clutch output. 

Wiring should go like this: from the heater switch control to a two-spade switch on the heater box, then out through the firewall to the AC clutch. 

[bigmal 225]

Thanks guys. I have checked and the power is getting to the clutch. It just comes from the wire to the fan so the voltage changes depending on fan switch position. I think it is wired incorrectly. I think the idea of the two-spade connector could be the trick. I just need to get some time to get back into it.

I'll report back shortly.

[barnett468 418]

7 hours ago, bigmal said:

Thanks guys. I have checked and the power is getting to the clutch. It just comes from the wire to the fan so the voltage changes depending on fan switch position. I think it is wired incorrectly.

yes it definitely is.

[danno 128]

The fan switch is different for an  AC car or Non AC car.   The AC switch has a connection on it that goes to the compressor through the thermometer switch.  That way the compressor can be fully  on no matter what the fan speed switch is set at.   If your switch is correct and wired correct, then you have a different issue.  The different issue could be dirty contacts in the fuse block.   But we can cross this when you find out about the switch.

[bigmal 225]

3 hours ago, danno said:

The fan switch is different for an  AC car or Non AC car.   The AC switch has a connection on it that goes to the compressor through the thermometer switch.  That way the compressor can be fully  on no matter what the fan speed switch is set at.   If your switch is correct and wired correct, then you have a different issue.  The different issue could be dirty contacts in the fuse block.   But we can cross this when you find out about the switch.

Hi Danno, going from memory there are 3 wires out of the fan switch that go to the resistor on the fan unit. There is a wire from the resistor unit that runs to the micro switch on the vent position selector. From there it runs to the clutch. The problem is when it comes off the resistor unit the voltage varies depending on fan switch position. I looked at changing where the clutch wire comes off the resistor unit but there is nowhere that doesn't change voltage.

[Midlife 814]

The AC clutch unit wiring does not interface with the resistor unit itself.  There is a separate and distinct anti-icing switch located somewhere on the heater box.  Your heater switch connector should have all five pins used, with a short green wire on one end with a black spade lead on it.  That wire goes to an AC mode switch located close to the heater switch with another green wire with black spade lead on that two pin switch.

It sure sounds like you have a non-AC box with AC wiring...

[bigmal 225]

18 minutes ago, Midlife said:

The AC clutch unit wiring does not interface with the resistor unit itself.  There is a separate and distinct anti-icing switch located somewhere on the heater box.  Your heater switch connector should have all five pins used, with a short green wire on one end with a black spade lead on it.  That wire goes to an AC mode switch located close to the heater switch with another green wire with black spade lead on that two pin switch.

It sure sounds like you have a non-AC box with AC wiring...

The heater box does have the anti-ice switch which I have checked and is not interfering with the voltage. I also have a spare complete heater/aircond unit which is the same. As the dash is back together at the moment I can't recall wire colours (colors for your guys). I have a wiring diagrams for the car but they don't go into detail for aircond control.

Would you have a diagram?

[Midlife 814]

[barnett468 418]

3 hours ago, bigmal said:

The heater box does have the anti-ice switch which I have checked and is not interfering with the voltage.

There is no way to test it because it can have 12 volts on both sides but not enough amps to operate the clutch. I had this exact same problem with a couple mustangs and it ended up being dirty and loose connections on this exact friggen switch, so I would clean all the connections really good, then make sure they are tight and even possibly bypass the switch until you get the clutch working properly by jumping both wire connectors together. As I previously mentioned, if you connect the clutch directly to the battery and it does this, it is not a power issue.

 

 

[bigmal 225]

1 hour ago, barnett468 said:

There is no way to test it because it can have 12 volts on both sides but not enough amps to operate the clutch. I had this exact same problem with a couple mustangs and it ended up being dirty and loose connections on this exact friggen switch, so I would clean all the connections really good, then make sure they are tight and even possibly bypass the switch until you get the clutch working properly by jumping both wire connectors together. As I previously mentioned, if you connect the clutch directly to the battery and it does this, it is not a power issue.

 

 

Thanks Barnett. I have put 12v strait to the clutch and it works perfectly. The power to the clutch is at 6v, 9v and 11v depending on fan switch position. The clutch will sometimes engage at 11v but not at a lower voltage

[bigmal 225]

4 hours ago, Midlife said:

Thanks Midlife. Looks like my power for the clutch does not come off the fan switch but the resister on the fan itself. I need to get back into it and confirm. II think this is the issue.

[barnett468 418]

49 minutes ago, bigmal said:

Thanks Barnett. I have put 12v strait to the clutch and it works perfectly. The power to the clutch is at 6v, 9v and 11v depending on fan switch position. The clutch will sometimes engage at 11v but not at a lower voltage

Yes, and I agreed that the clutch will not work if you leave it wired that way so i thought you were going to change it and wire it differently, so i am confused as to what you want to know at this point or what you are doing now.

 

[bigmal 225]

2 minutes ago, barnett468 said:

Yes, and I agreed that the clutch will not work if you leave it wired that way so i thought you were going to change it and wire it differently, so i am confused as to what you want to know at this point or what you are doing now.

 

All good. Will be using the wiring diagram to make sure the clutch wire comes from the correct source. Thanks.