Electrical Ac Issue Help Needed

ggradtech

Active Member
Jun 17, 2016
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My 92 Mustang has recently been converted to R134. When that was done, car was using a Megasquirt standalone ECM. I decided to go back to a stock ECM....long story. When the car uses the "stock" ECM, my compressor will kick on only for a second or 2. It will run normally with the Megasquirt computer and not turn off though. Could it be that the Megasquirt somehow bypasses a relay like the WOT clutch one that the stock ECM needs? My low pressure relay was changed when they did the R134 conversion and it's not low on refrigerant. Any ideas? Thanks!!
 
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My 92 Mustang has recently been converted to R134. When that was done, car was using a Megasquirt standalone ECM. I decided to go back to a stock ECM....long story. When the car uses the "stock" ECM, my compressor will kick on only for a second or 2. It will run normally with the Megasquirt computer and not turn off though. Could it be that the Megasquirt somehow bypasses a relay like the WOT clutch one that the stock ECM needs? My low pressure relay was changed when they did the R134 conversion and it's not low on refrigerant. Any ideas? Thanks!!
I know nothing about the MS system, but @a91what will know, he's our guru on the MS stuff.

By the way @a91what , @madmike1157 will be wanting to talk to you.
 
I know nothing about the MS system, but @a91what will know, he's our guru on the MS stuff.

By the way @a91what , @madmike1157 will be wanting to talk to you.
I'll get with mike.

The MS is a fantastic system if you know what your doing. Check the high pressure switch could be kicking the system off. Or you could try the system a few times and then pull the codes off the stock ecm. This will help @jrichker figure out what you may need to do.

As far as the MS and AC is concerned it's up to the installer to figure out what the system needs when wiring the unit. Check out some wiring diagrams and see what switches go back to the ecm. Jrichker can help with that as well.
 
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86-93 Mustangs only have a WOT relay and a low pressure cutoff switch in addition to the A/C control panel on the console above the ratio.

The WOT relay is controlled by the stock engine control computer. It is pin 54, pink/yellow wire.
The WOT relay shuts off the A/C when the engine goes to WOT. The computer provides a ground to make the relay provide power to the A/C clutch. You can ground the Pink/Yellow wire to force the relay to close the contacts and provide power to the A/C clutch.
This is for test purposes only!!! Do not go to WOT with the pink/yellow wire jumpered to ground, it may damage the A/C compressor.

a9x-series-computer-connector-wire-side-view-gif.71316.gif


eec-iv-computer-connector-for-5-0-mustang-gif.88243.gif



Diagrams courtesy of Tmoss & Stang&2birds

Fuel, alternator, A/C and ignition wiring
fuel-alt-links-ign-ac.gif


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

94-95 Mustang wiring diagrams
http://www.veryuseful.com/mustang/tech/engine/#95-95Diagrams

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057
 
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