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My AC system has been problematic recently on 2014 Ford with barely 31000 miles.

Its uses Visteon 16 compressor. When driving, after some minutes, it will shut off for long enough until the vent blow warm air for 1 or 2 minutes. Then turn on again for some minutes, then shut off again, keep cycling like that. This cause the cabin to become warm when it shut off for that long. I find the AC stay cool when idling though. Also when the AC is on, my automatic transmission will change gear around 2500 - 3000 rpm, while when the AC off, it will change gear just around 1800 - 2000 rpm.

Any advice?

Thanks

  • With the AC on, your automatic transmission changes gear at a higher RPM range to accomodate for the increased engine load due to the compressor. The ECU knows that the compressor is running and probably tells the transmission to change gear at a higher rpm, either that or it somewhat senses the additional load on the engine. – Al_ Aug 17 '18 at 12:40
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The Visteon VS16 is a variable displacement compressor. It shouldn't cycle off and on. Evaporator temperature is regulated either by a mechanical control valve actuated by the suction pressure and set to not allow the suction pressure to get below the value that makes the evaporator cold enough to freeze up, or an electronic control solenoid valve actuated by a control unit. Look for any connectors and wires on the back of the compressor to check if it's the electronically controlled version (if there's no wire and connector on the back, it's the one with the mechanical control valve). Either way, it sounds like the compressor is destroking too much once the evaporator gets cold. It may be a defective control valve or sensor.

Might also be some moisture stuck inside the AC piping that freezes the evaporator's thermal expansion valve's needle shut until it thaws out (and this also makes the compressor destroke), but it's unlikely, since there's a dryer.

Begin with having the refrigerant charge evacuated and weighed by a licensed professional, like Solar Mike probably suggested (pressure doesn't tell anything about charge weight and these compressors, especially the ones with mechanical control valves, behave erratically when the charge level becomes too low, and can also be damaged by the inadequate lubrication flow peculiar of a low charge condition). Then have the system thoroughly vacuumed and the correct charge level put inside and check for any improvements.

  • It seems that mine only have power cable, so it is using mechanical control valve? So now there are 3 possible cause that i understand it : control valve issue, evap issue, and condenser issue. Do you know how i can narrow down the issue? My low side pressure at idle is around 38 psi on (90-95F) ambient. and high side at 225 psi. When revivng to 2000 rpm, low will go down to around 30 psi, and high to around 285 psi. But if I hold the rev long enough, compressor will stop compressing and low side will jump up to 40 psii. Based on that condition, do you able to tell anything? – hudarsono Aug 16 '18 at 5:53
  • I already went to 3 repair shop before, but none seems to find the root cause, mostly they deal with denso only, and one repair shop said that clutch was still engaging when it stop compressing at 2000rpm. he suspected the control valve, but can do nothing about it as he can't find the replacement control valve in here. – hudarsono Aug 16 '18 at 6:06
  • 38 psig and 40 psig in my R134A PT chart equate to 6°C and 8°C, which are definitely high evaporator temperatures (while 30 is ok being around 0-2°C). I'd suggest first checking charge weight (maybe it has already been done by the shop), and then giving the condenser a good cleaning and trying to seal any gaps between radiator and condenser (if not already sealed). If not, it's the control valve. If you want to check for any clutch disengagement yourself it's simple: look at the compressor clutch while someone is keeping the engine revved up. – Al_ Aug 16 '18 at 10:53
  • Anyway, can you see any frost on the high side and especially on the dryer? – Al_ Aug 16 '18 at 10:57
  • Check if the drier isn't clogged. I had similar issue, but for me it was about 20 minutes at highway speed. After stopping the car, after a while I got large puddle of water underneath. So apparently the water was filling the drier up and at some point, because of that, the A/C disconnected. After the excessive water escaped the drier, it was fine again. – Mark Aug 17 '18 at 6:55
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You should check the refrigerant level - or have it checked,

Also check that the condensor is not blocked with leaves, paper etc As if it cannot get rid of the heat it shuts down.

  • If it were a condenser airflow problem it wouldn't stay cool at idle and most importantly it wouldn't alternate between cool and warm air. – Al_ Aug 15 '18 at 11:11

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