Ford Fiesta Mk7 AC stops working at idle

[Vinjy]

So I got the the girlfriend's Fiesta down to the mechanics to have the AC leak tested and refilled which was great for the 2 hot days we had so far this summer. However, I took it for a drive the other day and noticed that when I stop at the lights or in traffic the AC stops working. So here is what I found with the AC turned on:

- The radiator fan turns on as it should if the AC button in pushed (or if the engine is warm) 

- At idle, circa 900RPM the AC does not work and the air is ambient

- At about 1500RMP the AC starts blowing beautiful cold air

From that limited info, does anyone have any ideas of what the problem could be? I read somewhere that AC won't turn on below a certain RPM but surely this cannot be the case that it won't turn on below 1500RPM???

 

[ThaiFiesta]

The engine usually speeds up at idle to compensate for the aircon being on. It sounds like yours isn’t doing that. Not sure what the fix is. Do you have an “Econ” button? Turn that off if it’s on and you might fix the problem, or there may be a setting in the menu. 

[Vinjy]

I don't have an econ button and there is no setting in the menu. I have gently increased the RPM until the AC kicks in and it is just about 1500 RMP that it kick in. I agree, the idle should increase but a small amount to compensate for the additional load but 500 extra RMP seems too excessive. I read that there is a valve in the compressor that controls when the compressor engage, could it be this that is failing? 

[iantt]

Sound like low on gas. Did it have any gas before it was refilled? If not the the leak is still there. 

[Vinjy]

Quick update, we had another really hot week and obviously the aircon was an issue again not working at rpm below 1500-1700. The faster the engine revs the colder the AC is. So I took the car to a local garage to check refrigerant levels and a leak test. No leak detected and no refrigerant was necessary. I checked and the clutch engages as it should when you turn on the AC and the pump runs at idle and the fan turns on as it should.  They suggested I should consider changing the expansion valve?

Does anyone have any ideas on where the issue could be?