Need AC help

[Eric1971]

Thanks all, I will use all these suggestions to investigate further as soon as I can. Hopefully later today.

 

[Eric1971]

Yes, it's the EATC

Do you have the EATC (automatic climate control) or is it manual? If EATC, the problem may be there Much simpler for manual, but I wouldn't trust the Haynes generic schematic -- look for the proper one for your model -- they are in the "Electrical and Vacuum Troubleshooting" booklet.

 

[Eric1971]

The only new thing to add is that in removing the LP switch, it blew out and broke the o-ring, so now I have to wait until I can go pick up a new one!

 

[1998Exp]

Yes, it's the EATC

Hope you already checked the A/C fuse and it's OK. Your next logical step is to check whether the A/C relay is good (swap with the fuel pump relay -- check your manual for location). If that doesn't solve the problem, you need to check the signal out of the PCM that operates the relay. This is "active low", so the relay coil gets +12V directly to one end, and current through it is enabled by the PCM grounding the other. Your wire colors may be different from mine and I don't want to mislead - you will need a complete schematic for your year model.
The relay is controlled by the PCM. With a manual climate system, it gets inputs from the HP and LP switches and the mode selector (A/C on in all positions except vent), and decides whether to turn the A/C relay on, also depending on engine load. In an EATC system, the PCM gets the input from the EATC instead of the mode selector. The EATC, in turn, uses the mode and temperature settings, two temperature sensors, and a sun load sensor. PCM failure on that particular function only is quite unlikely, so if you determined that the A/C relay coil is not energized, it's probably the EATC or one of its sensors. Replacing the EATC with a known good one may be the most practical thing to do next -- albeit quite expensive.

 

[Eric1971]

I had already checked the fuse, swapped the relay, and also tried to bypass the relay but need to try that again now that I have a wiring diagram. I'll have a manifold gauge set tomorrow to properly check high and low sides. Hopefully, I can get that replacement O-ring for the LP switch today.

I don't entirely trust my "jumps" on the connectors so once I have the new switches in and the gauges to verify all the pressures, this should all go more easily.

Hope you already checked the A/C fuse and it's OK. Your next logical step is to check whether the A/C relay is good (swap with the fuel pump relay -- check your manual for location). If that doesn't solve the problem, you need to check the signal out of the PCM that operates the relay. This is "active low", so the relay coil gets +12V directly to one end, and current through it is enabled by the PCM grounding the other. Your wire colors may be different from mine and I don't want to mislead - you will need a complete schematic for your year model.
The relay is controlled by the PCM. With a manual climate system, it gets inputs from the HP and LP switches and the mode selector (A/C on in all positions except vent), and decides whether to turn the A/C relay on, also depending on engine load. In an EATC system, the PCM gets the input from the EATC instead of the mode selector. The EATC, in turn, uses the mode and temperature settings, two temperature sensors, and a sun load sensor. PCM failure on that particular function only is quite unlikely, so if you determined that the A/C relay coil is not energized, it's probably the EATC or one of its sensors. Replacing the EATC with a known good one may be the most practical thing to do next -- albeit quite expensive.

 

[Eric1971]

Ok, so here we are today and everything is squared away with new switches, replacement o-ring, etc.
I ran the EATC self-test and got the 888.
I swapped and checked all relays and fuses. All, not just the AC ones.

I'm looking at the attached EATC diagram, starting at the top-left:

• Engine ON
• Controls set to "Max AC"
• ~14V coming into "A/C Clutch Cycling Pressure Switch", measured to ground
• Low-pressure switch is closed and passing voltage through
• ~14V coming into the "A/C high-pressure cut out switch", measured to ground
• High-pressure switch is closed and passing voltage through
• I don't know where/how to check what is getting to the PCM but its sending on the voltage to the relay so that seems OK(?)
• Tracing around the diagram through the PCM and on to the AC WOT cutout relay, at pin 85 of the relay socket, I have ~14V coming in when measured to ground
• Should I measure the voltage from pin 85 to pin 86 instead of directly to ground? (I did this and it came out the same)
• Pin 30 (to relay from fuse panel) I am reading 10-12.3V, mostly steady at 12.3V, measured to ground. That seems a little odd since everywhere else is reading 14V
• If I put in 12-14V from the battery (or anywhere else) to pin 87a (to A/C clutch), the clutch engages.
• But if I jump pin 30 to pin 87a, I get nothing.

 

[Eric1971]

I just noticed that the diagram says "When the A/C Cutout Relay is de-energized and A/C clutch cycling pressure switch is closed, current will flow to the A/C Compressor Clutch Solenoid which allows the engine to drive the compressor."

Based on my test steps above, the cutout relay is energized. I don't know why it would be unless the PCM has gone bad and that still doesn't explain why jumping the relay socket pins doesn't engage the clutch, so I'm still confused.

 

[Eric1971]

Got the manifold gauges and made sure high and low pressures are good. I did have to add a little refrigerant but the results from yesterday are the same and the AC clutch is still not getting engaged. Seems like it boils down to the PCM energizing the AC WOT relay. I don't know where to go from here.

While I manually powered the clutch so that I could charge the system, it was blowing nice and cold in the interior.

Anything I can try that might indicate if it's the EATC, or if the PCM itself is messed up?

 

[1998Exp]

Ok, so here we are today and everything is squared away with new switches, replacement o-ring, etc.
I ran the EATC self-test and got the 888.
I swapped and checked all relays and fuses. All, not just the AC ones.

I'm looking at the attached EATC diagram, starting at the top-left:

• Engine ON
• Controls set to "Max AC"
• ~14V coming into "A/C Clutch Cycling Pressure Switch", measured to ground
• Low-pressure switch is closed and passing voltage through
• ~14V coming into the "A/C high-pressure cut out switch", measured to ground
• High-pressure switch is closed and passing voltage through
• I don't know where/how to check what is getting to the PCM but its sending on the voltage to the relay so that seems OK(?)
• Tracing around the diagram through the PCM and on to the AC WOT cutout relay, at pin 85 of the relay socket, I have ~14V coming in when measured to ground
• Should I measure the voltage from pin 85 to pin 86 instead of directly to ground? (I did this and it came out the same)
• Pin 30 (to relay from fuse panel) I am reading 10-12.3V, mostly steady at 12.3V, measured to ground. That seems a little odd since everywhere else is reading 14V
• If I put in 12-14V from the battery (or anywhere else) to pin 87a (to A/C clutch), the clutch engages.
• But if I jump pin 30 to pin 87a, I get nothing.

ASSUMING that this is the correct diagram for your model:
1) Seems that you made a typo in what you wrote above, and you connected the battery to 87, not 87A, because according to this diagram the clutch is connected to 87, while 87A is not connected anywhere.
2) Your low voltage reading on pin 30 seems to indicate a high resistance (poor contact or a broken wire, barely touching) somewhere between the battery and pin 30. Did you measure this voltage with the 87 shorted to 30 (or the relay energized)? I'd guess you will see something close to 0 when doing so. If that's true, I would start looking carefully at the connections from the battery to pin 30 of the relay, starting with the contacts in the fuse holder.
Caution: DVMs have very high input resistance, which will often result in measuring what's called a "phantom" voltage on a de-energized line. Some DVMs have a special, "low impedance" mode for measuring in such situations. Otherwise, just hook up a small load (for example, a test light) across the DVM probes when measuring a line suspected of this. Good luck!

 

[Eric1971]

The AC is now working, for now... It seemed like the PCM was acting a little wonky in my testing so I did an overnight reset (battery disconnect), hooked it back up this morning, let it idle for 5 minutes, drove to the park and back without any AC since it was cool out and I was trying to avoid the continued frustration for one hour. Got home, hit Max AC and it worked like one would expect it to. Wish I had a better explanation but I'll take it!

 

[RickOTR]

I would first check to see if there was any freon in the system. Also check the accumulator for any signs of holes from rust. That's what was wrong with mine and after replacing it and all the seals (5), it was up and running again.

 

[Gary Crist]

After all you have been through, I wonder if the culprit
was/is the WOT relay cut-out.

 

[Eric1971]

The refrigerant was within the proper range.

I didn't replace the relay, just tested/swapped, and made sure it was OK.

I'm wondering if while trying to clear a fixed EGR error code a while back if I inadvertently failed to allow the engine to run/calibrate for 5 minutes after a reset and the PCM got "wonky" which I didn't notice was affecting the AC until now when it got hotter and I started driving a little after 10 weeks of sitting at home.

Thanks for all of the advice everyone!

 

[1998Exp]

The refrigerant was within the proper range.

I didn't replace the relay, just tested/swapped, and made sure it was OK.

I'm wondering if while trying to clear a fixed EGR error code a while back if I inadvertently failed to allow the engine to run/calibrate for 5 minutes after a reset and the PCM got "wonky" which I didn't notice was affecting the AC until now when it got hotter and I started driving a little after 10 weeks of sitting at home.

Thanks for all of the advice everyone!

That's unlikely. Enjoy your cool truck!
And if the problem returns one day, I humbly suggest referring to my previous post in this thread (#29).

 

[Eric1971]

That's unlikely. Enjoy your cool truck!
And if the problem returns one day, I humbly suggest referring to my previous post in this thread (#29).

I did integrate your post into my investigations. There was definitely a mistake in the diagram I posted as it clearly said one thing, but the diagram showed another. I did find a correct diagram with all the right wire colors and it was 100% the same except for that one 87/87a issue.

In fact, thank you for pointing that out! I have updated my previous post with the correct diagram since I know someone will find this thread when searching for their own AC solution and I'd hate to lead someone down the wrong path!

 

[Eric1971]

Question... in reading the above wiring diagram, there's a few things I can deduce, like "C123M/C123F" is a male-female connection.

Can someone tell me what the plain numbers, like 198 or 347 mean, and also the "S144"? S144 Looks like a 3-way connection but I'm not sure what I'd be physically looking for in the truck. Thanks!

 

[1998Exp]

Question... in reading the above wiring diagram, there's a few things I can deduce, like "C123M/C123F" is a male-female connection.

Can someone tell me what the plain numbers, like 198 or 347 mean, and also the "S144"? S144 Looks like a 3-way connection but I'm not sure what I'd be physically looking for in the truck. Thanks!

"S" means splice or crimp -- in other words, a 3-way connection like you thought. If you have access to the EVTM book for your model, it will have a list to identify the location of those splices by number. Otherwise, I don't think that wire numbers are useful for repair purposes.

Incidentally, I can no longer see your diagram attachment.

 

[Eric1971]

I don't know what the EVTM book is, but I do have 72-hour access to the service manuals on motorcraftservice.com. Would the info be in there?

Reposting the diagram. 100% sure this one is the right one!

 

[Eric1971]

I found it in the "location index". It says S175 location is "Near T/O to power distribution box". I think there's a short or bad connection somewhere between S175 and pin 30 of the AC WOT relay.

If it's not clear, the AC stopped working again, so the hunt continues.

 

[Eric1971]

Oh FFS, I went through the service pinpoint test for AC and it says it's the EATC controls: " REPLACE A/C, heater control switch. "

As annoying as it is to now need to try replacing the EATC unit, I'd have gladly paid the $20 for all this info a week ago!