Tricky Air Conditioner

[kingpolaris]

Ok, I'm don't consider myself an a/c newb but this rig is kicking my ass.

2003 Expedition Eddie Bauer

A/C kicks on as soon as i start the vehicle but only stays on for about 5 seconds. Refrigerant pressures are low (i tried jumping out the low pressure switch) but shouldn't the compressor cycle back on after the pressure comes up - like ever other car i have ever worked on. I've checked high and low side pressure switches, interior and exterior air temp sensors, clutch relay and diode and all are good. The only way i can get the a/c to stay on is to jump out the compressor relay located behind the lh headlight. the only thing i can think of is it might have a bad WOT switch (wherever that is), a bad coolant temperature switch (again, wherever that is) or the dreaded bad pcm?

I'm running out of things to check so any advise would be awesome.

Thanks!

 

[Skauber]

Couldn't it just be low on refrigerant?

 

[kingpolaris]

Couldn't it just be low on refrigerant?

Jumped the low pressure switch.

 

[Hamfisted]

Are you trolling us ?
Why wouldn't you just add some freon to the system rather than "jump" system safety switches ? The issue is "kicking your ass" ? Take it to a shop. Don't ruin it.

 

[kingpolaris]

Are you trolling us ?
Why wouldn't you just add some freon to the system rather than "jump" system safety switches ? The issue is "kicking your ass" ? Take it to a shop. Don't ruin it.

i jumped the switch because it is a ***** to get a meter on the low pressure switch. suction pressure switch is fine, freon is fine.

 

[Skauber]

If you jump the low pressure switch, and it turns on, logic says that the pressure is low and the switch opens to protect the compressor from running dry, right? You need to connect an AC manometer on it to check the pressures, if it's low then you probably have a small leak somewhere. Just adding some freon is not gonna permanently fix your problem and may even be illegal to do without verifying that you don't have a leak, depending on where you are located. Anyway, check your pressures, if you don't have the tools to do that then it's time to contact a AC specialist.


Edit: it's a bit unclear from the opening post, but you say "Refrigerant pressures are low (i tried jumping out the low pressure switch)", and then "The only way i can get the a/c to stay on is to jump out the compressor relay". Have you checked the pressure in the system with a manometer? And does this mean that if you jump the low pressure switch, it does NOT turn on, but only when you jump the relay?

 

[Skauber]

BTW, the few seconds the compressor runs when starting the engine is by design. It does that regardless of the settings on the AC-system. When starting the engine, the AC compressor will engage for a few seconds to circulate the system, it is a preventive measure to ensure that the oil doesn't accumulate in the compressor and cause leaks, a problem commonly seen in vehicles after winter when the AC hasn't been used for more than 6 months.

 

[stamp11127]

Any advice.....go buy a good set of gauges and diagnose the correct way. Winging it is a waste of time.

 

[kingpolaris]

I've got a good set of gauges, a vacuum pump, a weight scale, a full bottle of 134a (30lb), and about every other tool needed to fix this problem - i hope.

I just got this rig and this is my first no cool experience with an expedition but I'm not totally unexperienced when it comes to ac (i have a bs in hvac engineering - not that that matters in this situation).

i guess i needed a little more of a back story on this. i received this ford from my uncle...for free. It had a blown spark plug, no ac, and a few other problems. i finished the spark plug repair last week (super fun) and now it runs ok. I'm still chasing problems, e.g. code P0356 (F ignition coil), so i decided to tackle the no ac problem while i wait for parts. i hooked up my gauges and noticed that my pressures where over 100 psig on both high and low sides which seemed normal. i noticed that someone put leak detection dye into the system so i recovered the freon and pulled a vacuum. system held a vacuum for about an hour with no movement in the gauges - sweet no leaks. i began to weigh fresh freon back into the unit (58 oz is factory charge) and got about 10 oz into the system before all pressures equalled out and system would accept no more freon. like every other vehicle system that i have ever worked on in the past i started the vehicle and tried to fill the system through the suction side while the compressor cycles. i could only charge the system for about 5 seconds before the system would kick out on something and never come back on (not sure at this point but i and everyone here would assume low pressure). systematically jumped out the low pressure switch, high pressure switch (multimeter indicates that that one is good), pulled and verified that the interior and exterior temp seniors were ok with an ohm meter. i replaced the relay (and diode) thinking that it might have a weak coil unable to handle the electrical current but no change. the only way i can get the ac to stay on is to jump out this relay. i had to take a break (before i raged) and a look for answers online hoping someone out there has experienced my pain. at this point i think it might be the WOT but I'm not sure how to check it. any useful advise would be awesome.

here is what i found on ALLDATdiy

"The A/C compressor clutch will only be engaged by the PCM if all of the following conditions are met:
The climate control assembly is set to a mode which provides an A/C request to the PCM.
The A/C thermostatic switch is reading a temperature above 37°F .
The high pressure cutoff switch is not open due to excessive pressure in the high side of the refrigerant system.
The low charge protection switch is not open due to insufficient low side refrigerant system pressure.
The A/C compressor relay is switched to the closed position by the PCM.
The engine coolant temperature is not excessively high.
The PCM has not detected a wide open throttle (WOT) condition."

i will not take this vehicle to a mechanic so stop advising that...please.

Thanks again!

 

[Skauber]

Ok, thanks. That does clear things up a bit more, and it's easier to advice when we know a little more about the background and of course your own abilities and qualifications. I have similar qualifications myself when it comes to HVAC systems.

That said, there are no WOT switch, this is determined by the PCM based on the TPS. What may be the cause for compressor not engaging is if the PCM thinks it's too cold outside, does the outside air temp display work? That sensor is located in front of the condenser, behind the front grille. What type of AC unit do you have? The digital climate control with dual zones, or the standard manual control with manual fan and temp selector?


EDIT: On a side note, do you have any sort of diagnostic OBD scanner? Like the OBDLink MX? If you do, you can download FORScan for Windows, which gives you almost the same access to read data PID's as the dealer has with their scantool.

 

[kingpolaris]

The outside temp display works (95F all ready - flm). i also pulled the sensor and checked the ohms last night, room temp and in a glass of ice - ohms matched specs.

dual zones with digital climat control.

i do have an obd scanner (innova 3100) which is currently flashing a p0356. i think i can download a ford specific program for it, is it worth getting?

could the pcm be bad? im working on the p0356 code right now and i have found that coil #6 has a resistance reading 10x's of the others on the input conector from the pcm at the coil and i cannot find any shorts in the wire harness. i ohmed out the ignition coils and all seem good (coil circuit complete/closed). i read somewhere that bad coils can kill drivers in the pcm. could a this be my problem? i jumping back on the ford to dig more into the harnees now to look for shorts.

thanks and any other advise would be great.

Ok, thanks. That does clear things up a bit more, and it's easier to advice when we know a little more about the background and of course your own abilities and qualifications. I have similar qualifications myself when it comes to HVAC systems.

That said, there are no WOT switch, this is determined by the PCM based on the TPS. What may be the cause for compressor not engaging is if the PCM thinks it's too cold outside, does the outside air temp display work? That sensor is located in front of the condenser, behind the front grille. What type of AC unit do you have? The digital climate control with dual zones, or the standard manual control with manual fan and temp selector?


EDIT: On a side note, do you have any sort of diagnostic OBD scanner? Like the OBDLink MX? If you do, you can download FORScan for Windows, which gives you almost the same access to read data PID's as the dealer has with their scantool.

 

[Skauber]

If it was a bad PCM driver for the AC, you should be able to see the PCM commanding AC to ON with the scantool. If it's not commanding the AC to ON, then there's something it's not happy with. You should be able to see the inputs as well. I'm not familiar with your scanner, but when using a bluetooth or USB OBD adapter like the OBDLink MX and FORScan in Windows, you can read all these parameters. It's useful to determine if the PCM might not receive an input from a switch, like low or high, and that prevents it from engaging the AC. Since you've already done a great deal in diagnosing it by verifying that the system has a correct charge, and checking all the sensors and switches as well as jumping the relay to turn it on, the next step is to diagnose it through the PCM to verify that all inputs has correct signal, and if the PCM is trying to engage the compressor or not. FORScan on Windows is free, but you'll have to buy the adapter as I don't think the Innova scanner can support it.

 

[kingpolaris]

If it was a bad PCM driver for the AC, you should be able to see the PCM commanding AC to ON with the scantool. If it's not commanding the AC to ON, then there's something it's not happy with. You should be able to see the inputs as well. I'm not familiar with your scanner, but when using a bluetooth or USB OBD adapter like the OBDLink MX and FORScan in Windows, you can read all these parameters. It's useful to determine if the PCM might not receive an input from a switch, like low or high, and that prevents it from engaging the AC. Since you've already done a great deal in diagnosing it by verifying that the system has a correct charge, and checking all the sensors and switches as well as jumping the relay to turn it on, the next step is to diagnose it through the PCM to verify that all inputs has correct signal, and if the PCM is trying to engage the compressor or not. FORScan on Windows is free, but you'll have to buy the adapter as I don't think the Innova scanner can support it.

Which adapter did you get and where did you get it. I found a few bluetooth adapters in town but i cant find any support info in FORscan's forum - Bosch and a Actron/U-SCAN.

 

[Skauber]

Amazon.com: ScanTool 426101 OBDLink MX Bluetooth: OBD Adapter/Diagnostic Scanner for Android & Windows: Automotive

 

[kingpolaris]

Amazon.com: ScanTool 426101 OBDLink MX Bluetooth: OBD Adapter/Diagnostic Scanner for Android & Windows: Automotive

Thanks!

 

[stamp11127]

Since you have the tools and the education in a/c, step back from the problem and look at your following statement:

"i began to weigh fresh freon back into the unit (58 oz is factory charge) and got about 10 oz into the system before all pressures equalled out and system would accept no more freon"

What would cause "all pressures to equal out"? And what pressure is that?

Not saying that this is a problem, but a leaky service port valve will stay under a vacuum with the connector still attached. Now I include new valves when servicing someones system. They don't like, move on down the road then.

 

[kingpolaris]

Since you have the tools and the education in a/c, step back from the problem and look at your following statement:

"i began to weigh fresh freon back into the unit (58 oz is factory charge) and got about 10 oz into the system before all pressures equalled out and system would accept no more freon"

What would cause "all pressures to equal out"? And what pressure is that?

Not saying that this is a problem, but a leaky service port valve will stay under a vacuum with the connector still attached. Now I include new valves when servicing someones system. They don't like, move on down the road then.

Pressure - Temperature Chart for HFC-134a

All pressure equal out because of the simple fact that the pressure in the bottle matched the pressure in the ford (i hate heating a bottle to force freon out). unfortunately you can't pore the freon in like oil or water. i guess i don't have "every" tool needed, a $4500 refrigerant transfer cart would be awesome - lol. even if i could get all the freon in i'm 100% sure that the ac still will not work.

I wish it was as simple as a leaky schrader valve.

I leading towards a bad pcm. i have a friend that is a ford mechanic coming over tomorrow with a real scanner. hopefully he will be able to shed some light on this. i feel that i have searched the entire internet with no luck.

thanks again for the suggestions.

 

[stamp11127]

To me when someone states the pressures equalled out that means both sides, low and high are equal. I don't take it as the low and high side pressures are within spec for the ambient temp.

You also stated the the system was under vacuum prior to refilling. I doubt 10oz would put the low and high sides anywhere near spec since that would be @1/5 of the charge. There is an error somewhere.

 

[kingpolaris]

To me when someone states the pressures equalled out that means both sides, low and high are equal. I don't take it as the low and high side pressures are within spec for the ambient temp.

You also stated the the system was under vacuum prior to refilling. I doubt 10oz would put the low and high sides anywhere near spec since that would be @1/5 of the charge. There is an error somewhere.

i guess i wasn't specific. ac system (ford), both high and low, was equal to the pressure in freon bottle.

doubt away but it's really not that uncommon, no error (well there's an error somewhere - system is still not running, lol). outside temp (and ford) when i was charging the system was about 105F (socal high desert). freon container was about 78F. once the "cool" freon entered the hot system (ford) the temperature differential equalled out faster than if i was in a cooler climate or if my freon was 1. a 100% liquid charge or 2. hotter than the system (ford).

is there another "secret" low pressure switch somewhere other than the one near/on the txv in the system that you know of that i can check or bypass or...is it possible that a bad pcm could prevent the compressor relay from closing. my theory is that the pcm isn't seeing a sensor input even though they all check good. i think the pcm already has a bad driver for the #6 ignition coil (75% sure) so maybe there is more than one issue with it. i wish i had a good sacrificial pcm that i could try.

 

[Bedrck47]

Stamp is he by chance related to King Brad? I always love these type that come on and brag about having a BS in something and do want to listen to the people they came on the forum seeking advice from.