96 explorer a/c electrical question

[koda2000]

Yes the PCM controls the AC compressor clutch in the Gen II explorer.

Real PITA when you try to convert Rangers to use our AC system because in a Ranger the dash controls the AC clutch...silly Ford

Do you think the reason the PCM is involved is because or the Sun and temp sensors on the right side of the dash?

 

[IanL]

Is it possible that the PCM generates the 3.6V as a reference signal? I recently watched a SMA YouTube video recently where this was happening on a vehicle where there was a 12V open circuit due to bad wire. This was on a newer vehicle though. IDK that the PCM on the Gen II Explorer's is involved with A/C compressor operation.

I dont think it is a reference signal. According to the posted diagram, the same voltage source is applied to all safety switches, as they are in series, and to pin 30 of the WOT relay. If I read 3.6 volts at pin 30 I should read 3.6 v at the Clutch connector and the Low pressure sw. I read 0 volts. Remember, all connectors were disconnected and jumpered to remove the active device in order to preclude shorts or high resistance problems through that device. I think the 3.6v reading is bogus, and I have an open circuit from the voltage source. EATC, open wire, who knows.

 

[IanL]

Do you think the reason the PCM is involved is because or the Sun and temp sensors on the right side of the dash?

The PCM has to trigger the WOT relay in order to allow current to pass to the compressor clutch coil. It does not supply 12 volts to the safety switches or cycling relay. That circuit is Hot when ignition is on or engine is running, whether the WOT relay is energized or not. The WOT relay is cycled by the PCM module because it monitors engine load. Its purpose is to protect the drive train regardless of creature comfort by disconnecting the AC to reduce engine load if required when climbing a long or steep grade. Thats why WOT stands for Wide Open Throttle. You have your foot in it climbing a grade, its hot outside, and are placing the drive train in a unnecessary load according to the PCM.

 

[IanL]

Thanks everyone for your help.
I think the problem is in the EATC module for the following reasons
I disconnected the AC clutch solenoid and hard wired it to a on off switch that i installed under the dash.
I used the High Pressure Cut Off switch 12 volt source, downstream of the switch, to power the loop.
This way I can manually cycle the AC clutch.
The loop functioned as designed and the compressor engaged and i get cold air at the registers.
However, with engine running and a digital meter connected to the , now disconnected clutch connector, I read voltage readings from 0 volts to 11 volts depending on EATC setting, ie max AC, Automatic with a requested set point, blending door setting etc. and the worst thing was the voltage reading appeared to be random and non repetitive.

I believe my work around would be ok if I manually cycled the clutch periodically .
This is based on a rather dangerous assumption.
1. With a functional EATC The compressor is cycled off when the user setpoint is achieved.
2. The compressor is cycled back on when cabin temperature is above setpoint by some margin
3. Allowing for setpoint deadband, loop hysteresis, and overall loop accuracy, I assume this to be between 3 and 5 degrees so as not to create a continuously cycling clutch. Not sure of the algorithm with respect to temp drop over time
4. If ( and this is the dangerous assumption) setpoint is never achieved, ie. AC system age, then the compressor is always on.
5. If max AC is requested, then the compressor is always engaged, never cycled. and the only protection is the High Pressure Sw.

Assuming the above is reasonably true I should be ok to operate manually while I remove the EATC and service / replace it.
Anybody please let me know if this is not ok

 

[koda2000]

Thanks everyone for your help.
I think the problem is in the EATC module for the following reasons
I disconnected the AC clutch solenoid and hard wired it to a on off switch that i installed under the dash.
I used the High Pressure Cut Off switch 12 volt source, downstream of the switch, to power the loop.
This way I can manually cycle the AC clutch.
The loop functioned as designed and the compressor engaged and i get cold air at the registers.
However, with engine running and a digital meter connected to the , now disconnected clutch connector, I read voltage readings from 0 volts to 11 volts depending on EATC setting, ie max AC, Automatic with a requested set point, blending door setting etc. and the worst thing was the voltage reading appeared to be random and non repetitive.

I believe my work around would be ok if I manually cycled the clutch periodically .
This is based on a rather dangerous assumption.
1. With a functional EATC The compressor is cycled off when the user setpoint is achieved.
2. The compressor is cycled back on when cabin temperature is above setpoint by some margin
3. Allowing for setpoint deadband, loop hysteresis, and overall loop accuracy, I assume this to be between 3 and 5 degrees so as not to create a continuously cycling clutch. Not sure of the algorithm with respect to temp drop over time
4. If ( and this is the dangerous assumption) setpoint is never achieved, ie. AC system age, then the compressor is always on.
5. If max AC is requested, then the compressor is always engaged, never cycled. and the only protection is the High Pressure Sw.

Assuming the above is reasonably true I should be ok to operate manually while I remove the EATC and service / replace it.
Anybody please let me know if this is not ok

I agree your EATC is likely your issue. I told you this early on. Your assumptions regarding compressor clutch operation are incorrect. The compressor should never run continuously, If it did your evaporator would freeze up, that's why the compressor cycles. Your blend door has nothing to do with A/C operation. It just blends warm and cold air depending on the doors position. Your compressor should engage and run for around 8-10 seconds then disengage for a similar amount of time before re-engaging. I believe this is controlled by the HIGH pressure switch. If your interior temp set-point is reached, the compressor may stay disengaged for a longer period of time, but I always run my A/C on MAX/60 degrees when I use A/C, so I don't know if the interior temp point has any effect on compressor cycling. Your compressor can run at any setting except VENT. This is done to remove humidity from the cabin. If you're low on refrigerant your compressor will cycle more quickly (engage for 4-5 seconds and then disengage for a similar amount of time). I have owned 4 EATC equipped Gen II Explorers/Mountaineers, this is how they functioned. I currently have a quick cycling compressor and insufficient cooling on my '01 Sport Trac (w/manual HVAC controls) because it is low on refrigerant. I plan to add some refrigerant today.

You can remove your EATC, take it apart and check the solder connections on the circuit board. I suspect that the solder joints for the compressor relay are broken. This condition has been reported here multiple times. Re-soldering the relay's connections has fixed the problem for others. If you don't want to do this, you can have your EATC tested/repaired for around $100.

 

[IanL]

I agree your EATC is likely your issue. I told you this early on. Your assumptions regarding compressor clutch operation are incorrect. The compressor should never run continuously, If it did your evaporator would freeze up, that's why the compressor cycles. Your blend door has nothing to do with A/C operation. It just blends warm and cold air depending on the doors position. Your compressor should engage and run for around 8-10 seconds then disengage for a similar amount of time before re-engaging. I believe this is controlled by the HIGH pressure switch. If your interior temp set-point is reached, the compressor may stay disengaged for a longer period of time, but I always run my A/C on MAX/60 degrees when I use A/C, so I don't know if the interior temp point has any effect on compressor cycling. Your compressor can run at any setting except VENT. This is done to remove humidity from the cabin. If you're low on refrigerant your compressor will cycle more quickly (engage for 4-5 seconds and then disengage for a similar amount of time). I have owned 4 EATC equipped Gen II Explorers/Mountaineers, this is how they functioned. I currently have a quick cycling compressor and insufficient cooling on my '01 Sport Trac (w/manual HVAC controls) because it is low on refrigerant. I plan to add some refrigerant today.

You can remove your EATC, take it apart and check the solder connections on the circuit board. I suspect that the solder joints for the compressor relay are broken. This condition has been reported here multiple times. Re-soldering the relay's connections has fixed the problem for others. If you don't want to do this, you can have your EATC tested/repaired for around $100.

Thanks for your help. I will try to repair the EATC
Also I did say my assumptions were dangerous didn't I.