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  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
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Electrical Foxbody AC System Issue!

  • Thread starter Thread starter mattskidooford
  • Start date Start date Jul 28, 2021
M

mattskidooford

New Member
Aug 23, 2018
1
0
1
Connecticut
Jul 28, 2021
#1
  • Jul 28, 2021
  • #1
I have followed Jrichker detailed steps on getting AC compressor Clutch to engage.

At WOT relay i have no power to black yellow wire.
I have 12V to Pink LT Blue as well as 12V to Red.
I Grounded the Orange LT/Blue wire with a good ground, and still didn't see 12V.
I then went and bought a new relay and still the same issue.

In simple terms:
RED: 12V
Pink/Lt Blue: 12 V
Orange/Lt Blue: 0
Black yellow: 0


I verified ground at AC Compressor Clutch as well as the I verified continuity from Black/yellow wire at relay to compressor clutch.


Info on car:
1987 Mustang, previous owner swapped an entire 1989 MAF harness in. I have installed a Fitech system. In other words the car is converted to a carb. I left the A9L in and harness to run AC. The only thing I removed was Injector harness at 10 pin connectors. I read the ground on the fire wall from the injector harness is for 02 sensors. Could removing this harness be my issue?

Any suggestions?

Thanks in advance for any help or to steer me in the right direction.
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,176
17,878
224
Massachusetts
Jul 29, 2021
#2
  • Jul 29, 2021
  • #2
Here's the wiring diagram for an 87-89 Mustang A/C and Heater system





Ground on the injector harness is for the O2 sensors. I would torubleshoot the WOT relay a bit more. If you ground the O/LB on the relay, it should close the relay with a click and you would have continuity from the Pk/lb wire over to the bk/y wire.
 

AnthonyA1234

5 Year Member
Aug 17, 2020
669
111
63
Florida
Mar 12, 2022
#3
  • Mar 12, 2022
  • #3
mattskidooford said:
I have followed Jrichker detailed steps on getting AC compressor Clutch to engage.

At WOT relay i have no power to black yellow wire.
I have 12V to Pink LT Blue as well as 12V to Red.
I Grounded the Orange LT/Blue wire with a good ground, and still didn't see 12V.
I then went and bought a new relay and still the same issue.

In simple terms:
RED: 12V
Pink/Lt Blue: 12 V
Orange/Lt Blue: 0
Black yellow: 0


I verified ground at AC Compressor Clutch as well as the I verified continuity from Black/yellow wire at relay to compressor clutch.


Info on car:
1987 Mustang, previous owner swapped an entire 1989 MAF harness in. I have installed a Fitech system. In other words the car is converted to a carb. I left the A9L in and harness to run AC. The only thing I removed was Injector harness at 10 pin connectors. I read the ground on the fire wall from the injector harness is for 02 sensors. Could removing this harness be my issue?

Any suggestions?

Thanks in advance for any help or to steer me in the right direction.
Click to expand...
Hello, could you please explain to me the process for getting the clutch to engage?
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,176
17,878
224
Massachusetts
Mar 13, 2022
#4
  • Mar 13, 2022
  • #4
AnthonyA1234 said:
Hello, could you please explain to me the process for getting the clutch to engage?
Click to expand...

Unplug the low pressure cutoff switch on the accumulator bottle. Jump the plug out with a piece of wire.

Assuming all the other electrical is intact, the compressor should cycle when you turn ac on
 

AnthonyA1234

5 Year Member
Aug 17, 2020
669
111
63
Florida
Mar 13, 2022
#5
  • Mar 13, 2022
  • #5
Mustang5L5 said:
Unplug the low pressure cutoff switch on the accumulator bottle. Jump the plug out with a piece of wire.

Assuming all the other electrical is intact, the compressor should cycle when you turn ac on
Click to expand...
Where is that switch located?
 

AnthonyA1234

5 Year Member
Aug 17, 2020
669
111
63
Florida
Mar 13, 2022
#6
  • Mar 13, 2022
  • #6
And also do I do this while the car is in auxiliary mode?
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,176
17,878
224
Massachusetts
Mar 13, 2022
#7
  • Mar 13, 2022
  • #7
AnthonyA1234 said:
Where is that switch located?
Click to expand...

Pass side firewall. There’s a bottle mounted to a bracket with a plug on top. Unplug and junp that.


Ac compressor won’t function in aux mode. Engine needs to be running
 
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