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Ford Expedition AC problem

cjd on Thu July 29, 2010 10:53 PM User is offline

Year: 2006
Make: Ford
Model: Expedition
Engine Size: 5.6L
Refrigerant Type: 134a
Ambient Temp: 92
Country of Origin: United States

My 2006 Expedition with front and rear A/C started intermittentally blowing cool air and then ambient air on a long trip this last weekend.

I stopped along the way and had a service shop check the refrigerant. They said it was a little low and added some refrigerant with UV dye. For the remainder of the trip the A/C only blew ambient air.

Today, I had a local service shop check for refrigerant leaks and it was confirmed to have no leaks. I jumped the connector at the low pressure cycling switch and the A/C clutch did not engage.
I have tapped the clutch...it also will not engage.

Occasionally the clutch will engage for about 10 seconds at random...the A/C will blow cold when this happens.

Does anybody know what I should check next?
Thanks in advance for the help.

bohica2xo on Thu July 29, 2010 11:20 PM User is offline

The PCM controls the compressor via a relay in that vehicle.

The PCM gets it's data from the HPCO, the LPCO, and a "De-icing switch" located at the front of the climate control unit.

Given the intermittent nature of the problem, I would start with the relay & the fuse that feeds it. The relay is located in auxiliary relay box 1, left front of the engine compartment. The fuse is located behind the right kick panel at the central junction box. It is fuse #32.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Fri July 30, 2010 12:39 AM User is offline

Thanks for the help...

I checked fuse #32...it is OK

Is there any way to check the relay? or should I just replace it?

bohica2xo on Fri July 30, 2010 1:15 AM User is offline

A bad relay can be a pain to test. Pull it out & look at the plug terminals. Check for signs of heating or burning. Shake it - it should NOT rattle like a playskool item.

Re-install it & see if the A/C works for a cycle or two...

You can swap it with another relay in the panel - this only works if the other relay is not essential for operation obviously.

Or just replace it.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Fri July 30, 2010 11:07 AM User is offline

tested the relay.....it works but makes a squeeky noise as the contact closes.

Do I need to replace it?

mk378 on Fri July 30, 2010 11:58 AM User is offline

Did you swap it with another one like Bohica suggested, there should be a bunch the same on the truck. Actually swapping with something vital would be good, if that vital system now doesn't work you know the relay is bad.

Edited: Fri July 30, 2010 at 11:58 AM by mk378

bohica2xo on Fri July 30, 2010 12:46 PM User is offline

That "squeaky noise" would make me replace it. A good relay should make a single, fast click.

The problem with bench testing a relay is that you can energize the coil, and a meter or test light will show the contacts closed. But once you put a 6+ amp load on the relay, the voltage drop looks more like a resistor...

That relay is the most likely culprit. Relays are capable of odd faults due to their mechanical nature.

The three gates in the PCM side of things are the HPCO, LPCO, & a thermistor. The two switches usually just fail - and do not come back to life randomly. Thermistors can go bad, but again they either short, open, or go out of range - for good.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Fri July 30, 2010 2:00 PM User is offline

Just replaced relay...no change.

On the way to pick up the relay...the AC was "pulsing" on and off.

After replacing relay....nothing, just recycled air.

bohica2xo on Fri July 30, 2010 2:21 PM User is offline

Ah, new data.

A "pulsing relay" would be driven by the PCM. If you pull the codes it may indicate an A/C fault, but it can't tell you what is at fault.

The HPCO & LPCO are wired in series with the thermistor. Either one of those switches could be bad, or a broken wire could be the fault. Or it could be "cycling" on one of those switches, due to a real high or low pressure event.

You jumped the LPCO switch with no result. I would not jump the high side without a gauge set attached. I recommend a push button switch for a jumper in an HPCO switch test.

Don't feel bad about that relay. It probably has a half million cycles on it in the last 4 years, and replacing it gives you a test spare for the other half dozen relays like it in that vehicle.

B.


-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Fri July 30, 2010 2:55 PM User is offline

So, I should try to jump the HPCO now?

Could there be something going on with the refrigerant circuit that is causing the high or low pressure switch to kick the clutch off?....like an obstruction or problem with the compressor?

Edited: Fri July 30, 2010 at 3:12 PM by cjd

bohica2xo on Fri July 30, 2010 7:35 PM User is offline

You need system pressures to go any farther.

I clearly do NOT recommend jumping the HPCO unless it is done while observing the gauge set, and with a momentary contact switch to allow shutting the system down if a high pressure event is the cause here.

Like I said before, this may be a bad switch, broken wire or it may be cycling on the HPCO switch due to an actual event. There is no way to tell without a gauge set attached.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Fri July 30, 2010 9:05 PM User is offline

Update.....Pressure readings (94 D ambient temp)

125L 145H

Same if AC is off or on....clutch not engaging

Edited: Fri July 30, 2010 at 9:29 PM by cjd

bohica2xo on Sat July 31, 2010 4:35 AM User is offline

Make yourself a short jumper with a couple of male spade lugs on it.

Put the gauges on the system.

Pull the A/C relay.

Start the engine.

With the engine idling, insert the jumper into the relay socket load terminals - WATCH the High side gauge!

If you see the high side go over 300 psi, pull the jumper!

If it idles with pressures in the expected range, then it is the HPCO or the thermistor, or a damaged wire / connector in the control circuit. You have already tested the LPCO, and checked the fuse.

If the clutch fails to engage when you jumper the relay socket, the fault is with the clutch coil / wiring / connector. Stop the engine. Turn the key back on, but don't start the engine. Put the jumper in the clutch relay socket. Tap on the clutch face to be SURE it is not a gap issue you are chasing.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Sat July 31, 2010 12:35 PM User is offline

More data:

I pulled the A/C relay and jumped the load terminals.....

Clutch engages , cool air and 42L 225H on the gauges....ran for 15 minutes and it never went over 225 on the high pressure side.

So it is a bad thermistor or a damaged wire?......I just jumped the HPCO the same way I did the LPCO and it didn't help.


Another point of data:

I noticed after running fifteen minutes...there was no condensate on the garage floor. My wife (her car) mentioned to me a couple of weeks ago that there was some dripping on the passenger side floorboard. Might there be a clogged line and full drainpan sensor causing an issue? I don't know if cars have something like that....

Edited: Sat July 31, 2010 at 1:32 PM by cjd

bohica2xo on Sat July 31, 2010 5:22 PM User is offline

Well your refrigerant loop looks good.

Obviously the two most accessible switches are ok, and you don't see any damage to the wiring harness in the engine bay.

At this point either a Mitchell or Alldata subscription for the vehicle is in order. You can probably look at the wiring diagram, and decide if there is a way to check the thermistor in the circuit with a DVM. If you do need to replace the thermistor, you will need that info anyway.

The evaporator case does not have a level switch. The water on the floor is a bad sign, and you should clear the evaporator drain.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Sun August 01, 2010 3:34 PM User is offline

I search and found the discharge air tempature sensor (thermister)...with the help of Alldata

I jumped the sensor and guess what? Yep...bad sensor. I will replace.

THANK YOU..... bohica2xo for your expert help.


A huge BOOOOO to the TWO A/C shops that told me I needed a new compressor (quotes of $1600 and $850)....I knew something didn't add up with that diagnosis.

bohica2xo on Sun August 01, 2010 4:20 PM User is offline

You are welcome.

Sorry the diagnosis took the long way around. Typically a thermistor will either fail open, or closed - but forever. Occasionally they go way out of range.

The "pulsing" you described may have been the PCM looking for an in-range signal from the thermistor. I keep finding more & more self testing subroutines buried in newer PCM's....

Glad you got the problem pinpointed.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

cjd on Sun August 01, 2010 9:54 PM User is offline

Can't find the temp sensor any where on the Internet. I guess I will try the Ford dealership tomorrow.

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