This is a question in general about Fords. My 98 Ranger doesn't do it but a friend asked me if I could get some suggestions. He's got a 1987 Ford Mustang 5.0 with original factory a/c. He changed his compressor to a used one and it started running all the time whether the **** was off or on. He said he switched back to his original compressor and it still does it. I figured it might be something common for Ford a/c systems so I figured I would ask. I'm not sure why it would be unless the mode switch was bad. Any ideas?

 

The AC compressor in a Ranger, depending on outside air temperature, will cycle in all settings except Vent, Floor & Off. If the OAT is below 50F the A/C compressor won't cycle.

 

The 87 system should energize the compressor clutch in multiple settings.
A/C, Max A/C, Defrost, Defrost/Floor Mix.
It should not be energized in Vent or Floor or Off positions.

tom

 

If the A/C is running when the HVAC switch is in the off position then maybe the relay for the A/C is stuck in the on position? A total guess on my part that the A/C will have a relay. But if it does then you may be able to smack it with a wrench a few times to see if it loosens up.

 

^+1, Good reading catch on the A/C operating with the switch in the Off position, so yes, swap the A/C power relay out for a like known good one, or Thump the one in there now & see if it'll wake up & act right & let us know what you find.

 

Check the high pressure cut off switch. Mine was bad when I changed my compressor and caused me to blow a hose.