Thanks for reply. 'Not holding charge' was told to me by Kwikfit after dropping it in for an ordinary recharge with them. They didnt specify, which is why I have it in with another mechanic presently. Its he that says the controller unit is at fault.

The vents work great when normal heating is engaged. No problem there. Its just no cooling operation is possible currently.

A bit of chatGPT seems to suggest the module J255, which is part of the driver facing A/C control display apparently. Have you ever encountered failures with that that would nix the actual cooling operation of the system? V grateful.

I have seen a reference to a failed Air Quality sensor preventing AC from operating.

If Shi*Fit say AC isn't holding charge, I'd say it's a reasonable guess that there's a refrigerant leak.

Edited 19 September, 202519 Sep by Warrior193
typo

Ill try and get the failure mode from the mech today.

With HVAC leak issues; it is worth putting getting a reputable HVAC specialist to put in some UV green dye to identify leaks. Usual contenders are the Schrader valves (high pressure and low pressure) that can leak as well as the condenser located as part of the cooling package on the front of the car. The former takes 2 mins to fix, the latter requires a new condenser. Both operations require evacuations of the refrigerant from the vehicles.

Typically on the MK3 Octavia's / MK7 Golfs, VAG recommend that a regas is performed every 2-3 years. I can say that after about 30 months, the HVAC does need regassing. What happens is that the cooling gets 'asthmatic' and needs attention.

I'm guessing that the "AC operator" is the evaporator - which is where the Fridge system chills the cabin air, that ties in with needing to work behind the dash, or remove it.

I'm guessing that is what is wrong with my wife's 2015 VW Polo - but that is just a guess, I really should get it professionally leak/pressure tested instead of thinking the worst!

8 minutes ago, varaderoguy said:

With HVAC leak issues; it is worth putting getting a reputable HVAC specialist to put in some UV green dye to identify leaks. Usual contenders are the Schrader valves (high pressure and low pressure) that can leak as well as the condenser located as part of the cooling package on the front of the car. The former takes 2 mins to fix, the latter requires a new condenser. Both operations require evacuations of the refrigerant from the vehicles.

Typically on the MK3 Octavia's / MK7 Golfs, VAG recommend that a regas is performed every 2-3 years. I can say that after about 30 months, the HVAC does need regassing. What happens is that the cooling gets 'asthmatic' and needs attention.

... And yet my MY16 Octavia AC is still operating well, never been touched!

Having said that, have I put the Kiss of Death on it now? 😆

Dashboard removal would suggest that an evaporator leak is suspected, or somehow confirmed.

That is the bit that cools the air, and is indeed deep behind the dashboard.

Edited 19 September, 202519 Sep by Breezy_Pete

6 hours ago, Warrior193 said:

... And yet my MY16 Octavia AC is still operating well, never been touched!

Having said that, have I put the Kiss of Death on it now? 😆

My MY13 has never been touched either, works a treat.

13 minutes ago, ords said:

My MY13 has never been touched either, works a treat.

Blimey, my system is checked every two years by my independent specialist, usually around 10-15% loss of gas every few years. I just prefer to look after it as well as I do my engine, with regular maintenance.

Edited 19 September, 202519 Sep by paulski

So after a leak test, it is indeed the evaporator.

Mechanic says that taking apart the interior dash to access it, plus new unit, would be a two day job at around £450. Does that sound reasonable? I think it probably does?

For the amount of work involved, including materials, I think your answer must be yes.

On 19/09/2025 at 19:51, paulski said:

Blimey, my system is checked every two years by my independent specialist, usually around 10-15% loss of gas every few years. I just prefer to look after it as well as I do my engine, with regular maintenance.

Except - apart from pressure and visual tests, there isn't really any maintenance that can actually be done on the AC system.

On 19/09/2025 at 12:49, Warrior193 said:

I have seen a reference to a failed Air Quality sensor preventing AC from operating.

My AQS has never worked but the A/C works just fine.