A/c PROBLEM think it maybe a compressor

[Huff890]

The A/C clutch is about $100 new or you can buy a compressor from the junkyard with a working clutch for about $50. The puller is about $21 if you have to buy one, AutoZone may rent you one for free.

The clutch hub is usually what fails, the rubber shock damper shears off from the steel hub and plate. The pulley turns, but the hub doesn't when you power up the A/C.
www.rockauto.com Ford MOTORCRAFT Part # YB289A $39.00

The hub comes off without much problem if you have the puller. You don’t have to do anything with the refrigerant (R12 or R134a), you can replace the clutch without draining and refilling the system. The snap ring hiding inside the hub is the only tricky part.

Remove the nut; remove the snap ring (if present) and then remove the washer. Loosen the puller tool center bolt so that you can get the larger threaded section of the puller screwed into the clutch hub. Tighten up the center bolt on the puller and the clutch hub will come off.

Clutch hub puller tool

Part Number: 27002
Alternate Part Number: 59509
AutoZone and most other major auto parts chain stores will rent or loan the puller. Cost is $21.00 if they don’t have one to loan.


A few simple electrical tests are advised before popping out the wallet to buy a clutch assembly. With the engine running, use a test light connected to the 2 wires on the A/C clutch harness to make sure you have voltage when you turn the A/C on. If the system is low on refrigerant, the clutch will not engage (safety feature, keeps you from burning up the compressor due to no oil). There is an aluminum canister on the firewall with a large hose leading to the A/C compressor. There is a pressure switch on it with a 2 wire connector: pull the connector off and jumper the wires. The compressor circuit will power up, and the test light will light if the electrical circuit is good. This test is also a good way to check the compressor & clutch if the system is low on refrigerant. You can jumper the wires and the compressor will turn if the clutch is good.

The clutch also has a relay that shuts off when you go to WOT (wide open throttle). It is located on the passenger side inner fender well. The close proximity of the relay to the headers can cause the insulation on the wiring and the relay socket to deteriorate. The relay can become non functional when this happens.

Caution: replacing the A/C compressor seal requires removing the R12 refrigerant. By law you are supposed to recover it and not dump it to open air. I will leave that up to you...
The A/C compressor seal is less than $12. See AutoZone Santech A/C Compressor Shaft Seal Kit MT2039. You will need a pair of internal snap ring pliers to remove and install the seal snap ring

Diagram courtesy of Tmoss & Stang&2birds

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.

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

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

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

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 & pinout

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

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I jumped the connector on a.c switch next to the firewall used a test light on the connector side of the ac compressor and i have no power on both sides

 

[Huff890]

is there any chance my ignition module would affect this i have a zip tie temp fix but it affected my blower motor lights alot of things didnt work

 

[Huff890]

so i tested everything with a test light i had power and ground up from the a/c switch by the firewall to the diode so i upluged the diode and gave it power and ground from the batt. clutch still woundnt engage so i think i need to replace the diode on the clutch?

 

[jrichker]

so i tested everything with a test light i had power and ground up from the a/c switch by the firewall to the diode so i upluged the diode and gave it power and ground from the batt. clutch still woundnt engage so i think i need to replace the diode on the clutch?

The diode will not affect your problem; it just clamps the reverse voltage spike that happens when the clutch coil power is turned off.

Using a diode as a dampener in automotive circuits:

Theory of operation:
The diode acts as a surge absorber or one way gate. Anytime you turn the power off an inductive load (coil, motor, solenoid, etc) the collapse of the magnetic field creates a voltage spike of opposite polarity to the voltage applied. The positive wire sees a negative spike and the negative wire sees a positive spike. The diode is wired backwards so that it does not conduct during normal forward operation. When the magnetic field collapses, the diode sees the reverse polarity spike and clamps it. This prevents the spike from possibly damaging the rest of the electronics in the car.
When used to clamp spikes in automotive circuits, connect the lead that comes from the end of the diode that has the band on it to the positive side of the circuit. Connect it the other way and you will make smoke.

Diode markings

A properly functioning diode will measure very high resistance or open circuit in one direction. Reverse the meter leads and it will measure a lower resistance.

 

[Huff890]

The diode will not affect your problem; it just clamps the reverse voltage spike that happens when the clutch coil power is turned off.

Using a diode as a dampener in automotive circuits:

Theory of operation:
The diode acts as a surge absorber or one way gate. Anytime you turn the power off an inductive load (coil, motor, solenoid, etc) the collapse of the magnetic field creates a voltage spike of opposite polarity to the voltage applied. The positive wire sees a negative spike and the negative wire sees a positive spike. The diode is wired backwards so that it does not conduct during normal forward operation. When the magnetic field collapses, the diode sees the reverse polarity spike and clamps it. This prevents the spike from possibly damaging the rest of the electronics in the car.
When used to clamp spikes in automotive circuits, connect the lead that comes from the end of the diode that has the band on it to the positive side of the circuit. Connect it the other way and you will make smoke.

Diode markings

A properly functioning diode will measure very high resistance or open circuit in one direction. Reverse the meter leads and it will measure a lower resistance.

Yea but shouldn't I be getting power after that connector I have power all the way up to the a.c compressor harness

 

[jrichker]

Yea but shouldn't I be getting power after that connector I have power all the way up to the a.c compressor harness

Do you know how to use your meter to measure resistance?

 

[Huff890]

Do you know how to use your meter to measure resistance?

Yes

 

[Huff890]

Do you know how to use your meter to measure resistance?

I'm getting O.L. on the power side

 

[jrichker]

I'm getting O.L. on the power side

From your answer, I'll take it that you don't know how to use a meter to measure resistance.
Never measure resistance with the circuit power on. You will get inaccurate readings and may damage the meter.

Here's some help... https://www.wikihow.com/Measure-Resistance

If that didn't help, here are some more resources...

Google Search

Digest that and we'll start testing the components of the A/C clutch power circuit...

 

[KRUISR]

Fastest way to see if a/c clutch works is unplug the 2 wire connector on the compressor. This is power and ground to the clutch coil. Run jumpers from battery to the 2 wires with engine running. If clutch is working, pulley will start spinning when jumped. If clutch is working and A/C doesn't run normally, issue is elsewhere in wiring.

In my opinion (and was the reason in my case) the next possible cause would be the A/C clutch relay (looks same as fuel pump relay and is interchangeable). This can be jumped to test as well. On my 90 it is located passenger side near factory air box inlet. With engine running, jump the 2 heavier gauge wires at the relay. System will start if issue is a signal problem to relay or bad relay. If jumping works, can test relay resistance to see if it is good or simply replace relay.

I know this is not the troubleshooting guide and definitely not as thorough. It will give a ruling on clutch functionality in a couple minutes. It is not the fix, but can rule out clutch as the issue very quickly.

 

[Huff890]

From your answer, I'll take it that you don't know how to use a meter to measure resistance.
Never measure resistance with the circuit power on. You will get inaccurate readings and may damage the meter.

Here's some help... https://www.wikihow.com/Measure-Resistance

If that didn't help, here are some more resources...

Google Search

Digest that and we'll start testing the components of the A/C clutch power circuit...

I didnt have power to it I disconnected the a.c harness from the compressor and the connector on the side of the engine bay so yea I do know how to

 

[Huff890]

Fastest way to see if a/c clutch works is unplug the 2 wire connector on the compressor. This is power and ground to the clutch coil. Run jumpers from battery to the 2 wires with engine running. If clutch is working, pulley will start spinning when jumped. If clutch is working and A/C doesn't run normally, issue is elsewhere in wiring.

In my opinion (and was the reason in my case) the next possible cause would be the A/C clutch relay (looks same as fuel pump relay and is interchangeable). This can be jumped to test as well. On my 90 it is located passenger side near factory air box inlet. With engine running, jump the 2 heavier gauge wires at the relay. System will start if issue is a signal problem to relay or bad relay. If jumping works, can test relay resistance to see if it is good or simply replace relay.

I know this is not the troubleshooting guide and definitely not as thorough. It will give a ruling on clutch functionality in a couple minutes. It is not the fix, but can rule out clutch as the issue very quickly.

I jumped from my battery to the compressor and the clutch didnt do anything

 

[RonaldCarter]

It is the faulty compressor or there is some other issue with the ac unit. As such issues can get fixed by own, contacting experts is the only solution to such problems.