Tricky Air Conditioner

[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.