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  #1  
Old 10-21-2010, 07:46 AM
jonfal jonfal is offline
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Default Unique A/C problem

2005 Ford Ranger 4.0 XLT 4WD - 130k miles

6 months ago, I had the compressor replaced when the A/C clutch went after trying a "band-aid" that worked for all of 1 day. A/C has been working fine, now it just stopped. I've searched all over the forum and the internet, and can't quite narrow down what's wrong, so here's what I have done:

1) Took it back to place the replaced the compressor, as it was under warranty. Compressor works when power is put straight to it, and the A/C does work intermittently. System is fully charged. They say it's something electrical and mentioned an A/C control module. Estimated repair is $400 including a ~$200 part. (I have been taking cars there for some time, and this shop has a stellar reputation and has always done right by me).

2) All 3 knobs on the panel work. I can get the air to blow from lukewarm to hot by turning the temp. control knob, so I'm pretty sure it's not the blend door, nor is it a loose connection at the knobs.

3) Had someone watch the compressor NOT turn on while changing to a variety of settings.

4) Jumped the pressure switches to test the plugs, and nothing changed.

5) Checked and swapped both related fuses and relays and nothing changed.

So I have ruled out the control panel, the blend door, the compressor, the plugs, the pressure switches, the fuses or relays, and the system is fully charged. I have looked high and low for something called an A/C control/computer module and can't even determine what this is (although I did find out that with some A/C systems, they are tied into the ECM - gulp!).

Any ideas from you gurus?
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  #2  
Old 10-21-2010, 07:51 AM
dangerrangerdbd dangerrangerdbd is offline
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Default Re: Unique A/C problem

man it seems you did everything right. you pretty much named off every piece of advice.
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  #3  
Old 10-21-2010, 08:20 AM
jonfal jonfal is offline
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Default Re: Unique A/C problem

I certainly tried, and had 2 people taking a look at it as well (including one that grew with a dad as a mechanic I believe).

At this point I'm just trying to find out if the ECM could indeed be the culprit and the part that my mechanic is talking about, or if there is some other component I'm missing that would be able to be snagged at a junkyard. It's not that I doubt my mechanic, as much as it's that I don't have $400 to spend on it.

I'm tempted to grab the control panel with the 3 knobs from LKQ for $40, as they're the only local scrap yard I know of. I have read a few places that it can be the knob, but I doubt that, since I can make the air go from ambient/lukewarm to hot, and that would seem to rule out that panel or the sensors mounted behind the knob.
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Old 10-21-2010, 08:36 AM
rwenzing rwenzing is offline
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Default Re: Unique A/C problem

Quote:
Originally Posted by jonfal View Post
I have looked high and low for something called an A/C control/computer module and can't even determine what this is (although I did find out that with some A/C systems, they are tied into the ECM - gulp!).
There is no standalone A/C module - the compressor clutch is commanded directly by the PCM based on input from the HVAC panel and driving conditions. I don't buy the notion that the PCM is at fault here.

Basically, you should need 4 conditions for the PCM to be able to command compressor clutch operation.
  • Continuity through the low pressure cycling switch at the evaporator (open with too little pressure).
  • Continuity through the high pressure switch at the condenser (open with WAY too much pressure).
  • Continuity through the mode selector switch (open in OFF, VENT only or FLOOR only).
  • Continuity through the A/C clutch relay.

What I would do next:
  • Check fuse 27 in the Smart Junction Box.
  • Check fuse 25 in the underhood Distribution Box.
  • Check ground G103 (driver side inner fender apron, halfway back near Distribution Box)
  • Check ground G104 (driver side radiator core support, near the battery)
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Old 10-21-2010, 10:36 AM
jonfal jonfal is offline
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Default Re: Unique A/C problem

Rwenzing, thanks for that info. I had already checked and replaced both fuses, but checked them again just to make sure they were still OK.

As far as checking the grounds, I made need some help on that one, as I am a novice when it comes to much of the electrical systems (used to work on easily accessible diesel pumps, but there's no comparison to a gas loco engine). I looked in the Haynes and in my ops. manual, and no surprise, but there doesn't seem to be a diagram that illustrates where these grounds are. I have googled them as well, and do not see a guide to finding them. I will try to find them and sand them down when I do and give that a try, unless you've got a good link for a picture of where I'm looking!

EDIT - I found one ground the is roughly 6 inches in front of the distribution box (if that's the same thing as the underhood fuse box). It is close to the bracket that holds the underhood fuse box. Might this be G103? And I found another ground that is to the right of the radiator and that bolt actually shares a ground with an 8 inch ground from the battery. Might this be G104?

Last edited by jonfal; 10-21-2010 at 10:48 AM.
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Old 10-21-2010, 11:06 AM
rwenzing rwenzing is offline
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Default Re: Unique A/C problem

Quote:
Originally Posted by jonfal View Post
EDIT - I found one ground the is roughly 6 inches in front of the distribution box (if that's the same thing as the underhood fuse box). It is close to the bracket that holds the underhood fuse box. Might this be G103? And I found another ground that is to the right of the radiator and that bolt actually shares a ground with an 8 inch ground from the battery. Might this be G104?
That sounds right. As long as both are clean and tight and the wires are undamaged, they should be good to go.
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Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles

2003 XLT 2.3L M5OD-R1 reg cab, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid
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  #7  
Old 10-21-2010, 12:27 PM
jonfal jonfal is offline
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Default Re: Unique A/C problem

Well, the grounds look fine, and they were tight. However, something popped into my head, and I decided to swap the relay for the AC/Clutch with the Fog Lamp. Long story, but my windshield wiper pump hasn't been working, and I swapped that relay for the AC/Clutch relay about a week ago and the pump still didn't work, so I assumed it was the pump itself. I never thought that both the AC/Clutch relay and the wiper pump relay could be bad. However, I just remember that (wrong) assumption and put in the relay from the fog lamp which works, and now the compressor comes on.

However, it is cycling on and off repeatedly now, maybe on for 2 seconds, off for 5, and so on. I did some more research, and this points towards either low freon, which my mechanic ruled out, or faulty pressure switches. However, when I unplug either the high or low pressure switch, the compressor stays off completely until I either jump the pressure switch, or plug it back in. Even more odd is that if I rev my engine up and keep it around 2k RPM, the compressor will come on and stay on.

My thinking is that even if I had low freon, when I jump the low freon pressure switch, it should stay on (although I wouldn't want it to stay on for long and burn up the compressor).

Edit - I read about people having 2 very similar problems, and both refer to replacing a WOT relay. I have looked in my Haynes and in the Ford Manual, and do no see anything labeled a "WOT" or wide open throttle relay (the Haynes diagram barely address A/C wiring). However, I found that Mustangs and Explorers have the WOT relay in the main fuse/relay panel under the hood. Does anyone know if the WOT relay might be the same as the A/C Clutch relay? The A/C clutch relay is the only relay in that box other than the fuel Pump, wiper pump, auto-down window, and fog lamp relays, which makes me wonder if what is labeled as the A/C clutch relay may be the same thing as the WOT relay.

Last edited by jonfal; 10-22-2010 at 07:18 AM.
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