Topic: A/C Clutch Engagement Question

[Tiggie]

I asked this question on VMF but haven?t gotten the absolutely yes or absolutely not I am looking for. This is my first 1960s Ford A/C experience.

68

Factory A/C

A/C clutch is engaged at all times with the key on/engine off. Even with the system set to off. Seems odd that Ford would set it up this way. Extra load on the starter and battery is not optimal from my experience.

Once the car is started and vacuum builds, the clutch disengages as appropriate.

I need someone with first hand experience that I trust (you all)! It?s not a concours question but a question nonetheless.

[67gta289]

"A/C clutch is engaged at all times with the key on/engine off"
When you say that the clutch is engaged with the engine off, what is the position of the key?  If the key is still in run but the engine stalled, this is possible.  But if the engine was stopped via the key, the clutch power should be interrupted.

"Once the car is started and vacuum builds, the clutch disengages as appropriate."
The only way that vacuum could affect this is when the "A/C-defrost door arm" is moved off the AC control switch

I'll need to do some more digging, but if you could answer the question about key position that would help.  If you have power to the clutch with key off - engine off, we should get that problem fixed before going down any other rabbit trails.  Fixing that might solve more than one problem/symptom.

[RoyceP]

Any time the fan switch is "OFF" there is no power to the AC clutch. I recommend that you unplug the power to the clutch and see what the situation is.

The power circuit for the AC fan clutch also goes through an "icing switch" mounted on top of the evaporator / heater core housing. If ambient temperature is below freezing the AC clutch gets no power if the switch is working properly.

I suspect that you have one of two things going on - either the clutch is seized so it is on regardless of power, or someone has installed a home brew wire that supplies power to the clutch any time the key is on. 

I asked this question on VMF but haven?t gotten the absolutely yes or absolutely not I am looking for. This is my first 1960s Ford A/C experience.

68

Factory A/C

A/C clutch is engaged at all times with the key on/engine off. Even with the system set to off. Seems odd that Ford would set it up this way. Extra load on the starter and battery is not optimal from my experience.

Once the car is started and vacuum builds, the clutch disengages as appropriate.

I need someone with first hand experience that I trust (you all)! It?s not a concours question but a question nonetheless.

[67gta289]

Looking at some Ford documents, starting with the wiring diagram (attached), the power flow is:

1. From the ignition switch power source - need to confirm what key position(s) provide(s) power. 
2. Through a circuit breaker via wire 257
3. To the controller (mode,blower speed, and temperature blend door position)
4. Need to determine the exact conditions that will pass power to the clutch.  The blower switch diagram is not the easiest to decipher, but I can talk myself into the interpretation that any time the switch is off, power to the clutch is interrupted.  From this diagram there is no influence on the mode switch.  Of course the blend door positioning is via cable, and for completing the discussion that has no influence.
5. Out via wire 348 to the AC thermostat switch.  This switch is normally closed, and opens if the coil freezes over, allowing it to thaw before energizing the clutch again.
6. Out via wire 348A to the AC control switch.  I don't recall off hand the exact conditions under which this contact is closed vs. opened. 
7. Out via wire 348B to the AC compressor clutch.

More Ford docs to follow.

[67gta289]

These charts indicate that the clutch is controlled "by AC defrost door arm" position.

My interpretation is that in Max AC, Fresh AC, and Off positions (mode select), the clutch switch is "on".  In the Heat and Defrost modes, the clutch switch is "off".

Does anyone else see that?  Or do you have a different interpretation?

[RoyceP]

If you look at the chart it says the AC compressor is supposed to be switched off by the Defrost arm. That arm won't move unless the mode select is set to "DEFROST". It will still have power if you have HEAT selected.

The defrost switch is activated only in DEFROST mode.

In any case he needs to determine if there is power all the time and if so, why. If there is no power, or power when it's supposed to be there, then the clutch is defective.

[Tiggie]

Awesome replies. Once again never disappointed with the knowledge here. Let me try to help you help me.

"A/C clutch is engaged at all times with the key on/engine off"
When you say that the clutch is engaged with the engine off, what is the position of the key?  If the key is still in run but the engine stalled, this is possible.  But if the engine was stopped via the key, the clutch power should be interrupted.

"Once the car is started and vacuum builds, the clutch disengages as appropriate."
The only way that vacuum could affect this is when the "A/C-defrost door arm" is moved off the AC control switch

I'll need to do some more digging, but if you could answer the question about key position that would help.  If you have power to the clutch with key off - engine off, we should get that problem fixed before going down any other rabbit trails.  Fixing that might solve more than one problem/symptom.

Key on/engine off/never started clutch engages. Engine starts clutch disengages unless in the A/C or Max position.

Any time the fan switch is "OFF" there is no power to the AC clutch. I recommend that you unplug the power to the clutch and see what the situation is.

The power circuit for the AC fan clutch also goes through an "icing switch" mounted on top of the evaporator / heater core housing. If ambient temperature is below freezing the AC clutch gets no power if the switch is working properly.

I suspect that you have one of two things going on - either the clutch is seized so it is on regardless of power, or someone has installed a home brew wire that supplies power to the clutch any time the key is on. 

My fan switch could be bad if that is supposed to cut power to the clutch. It does get power in the off position. I have bench tested the icing switch (put it in the freezer!). It works as it should. Clutch is not seized. It disengages once the car starts and the vacuum motors do their thing.  Wiring is all stock, in good condition.

These charts indicate that the clutch is controlled "by AC defrost door arm" position.

My interpretation is that in Max AC, Fresh AC, and Off positions (mode select), the clutch switch is "on".  In the Heat and Defrost modes, the clutch switch is "off".

Does anyone else see that?  Or do you have a different interpretation?

This is nearly exactly what it?s doing once it?s running other than the clutch does cut off when in the off position. Which I am hoping is correct.

Looking at some Ford documents, starting with the wiring diagram (attached), the power flow is:

1. From the ignition switch power source - need to confirm what key position(s) provide(s) power. 
2. Through a circuit breaker via wire 257
3. To the controller (mode,blower speed, and temperature blend door position)
4. Need to determine the exact conditions that will pass power to the clutch.  The blower switch diagram is not the easiest to decipher, but I can talk myself into the interpretation that any time the switch is off, power to the clutch is interrupted.  From this diagram there is no influence on the mode switch.  Of course the blend door positioning is via cable, and for completing the discussion that has no influence.
5. Out via wire 348 to the AC thermostat switch.  This switch is normally closed, and opens if the coil freezes over, allowing it to thaw before energizing the clutch again.
6. Out via wire 348A to the AC control switch.  I don't recall off hand the exact conditions under which this contact is closed vs. opened. 
7. Out via wire 348B to the AC compressor clutch.

More Ford docs to follow.

I have pored over that diagram and get the same idea. I have the same question as you on your #6.

If you look at the chart it says the AC compressor is supposed to be switched off by the Defrost arm. That arm won't move unless the mode select is set to "DEFROST". It will still have power if you have HEAT selected.

The defrost switch is activated only in DEFROST mode.

In any case he needs to determine if there is power all the time and if so, why. If there is no power, or power when it's supposed to be there, then the clutch is defective.

I think that defrost arm is the only thing cutting my clutch on and off once the system has vacuum. I will try to verify tomorrow. The power is okay. It does switch on and off.

[RoyceP]

Sounds like a defective or bypassed fan switch.

[Tiggie]

Sounds like a defective or bypassed fan switch.

It?s not bypassed. But could certainly be defective!

Unfortunately, it?s below freezing in my garage right now so the icing switch won?t let the clutch engage at all. Will hopefully warm up in a bit.

[Tiggie]

Garage warmed up a little.

Can anyone confirm with first hand experience: with the fan switch OFF, the clutch should disengage? (It doesn?t right now).

[RoyceP]

Yes confirmed.

Garage warmed up a little.

Can anyone confirm with first hand experience: with the fan switch OFF, the clutch should disengage? (It doesn?t right now).

[RoyceP]

BTW this is ridiculously easy to troubleshoot. Unplug the fan switch. This will require removing the four screws securing the heat / AC control panel to the dash.

Garage warmed up a little.

Can anyone confirm with first hand experience: with the fan switch OFF, the clutch should disengage? (It doesn?t right now).

[Tiggie]

Pulled the two wire connector on the fan switch today. Continuity on the ?off? setting. Will be ordering a new switch. Thanks for you help everyone.

[RoyceP]

Glad you found it!

One thing,  67gta289 posted a photo of the 1967 wiring manual. The '68 is different with regard to the location of the circuit breaker and the wiring from the ignition switch. On your '68 the CB is located below the fuse panel.