Airco refrigerant pressure Climatronic - typical values?

[dieselV6]

Hi, 

2016 Skoda Octavia vRS TDI.

My airco stopped blowing out cold air, could have happened over time as due to covid car was not used much last 9 months.

 

No fault codes, I can adjust temperature, compressor is turning, can be switched on/off, refrigerant pressure changes when compressor is on.

I looked at VCDS measuring values for HVAC, and refrigerant pressure is around 5bar with airco off going up to perhaps 9 bar with airco on. What is a normal pressure in this measuring value?  

What does not look normal is temperature reading out of evaporator, it is pretty much outside temp+engine/sun heat, ie around 25deg when it's 15deg C outside.

 

Perhaps I just need to regas/add some leak sealer (last regas about 3 years ago when I bought the car, airco worked fine for at least 2 years afterwards). But would like to be sure.

 

What is normal refrigerant pressure range readable in the Advanced Measuring Values in Auto-HVAC (VCDS, OBD11)?

Help much appreciated.

 

Edited 26 April, 2022 by dieselV6

[J.R.]

The high & low side pressures are relative to the ambient temperature, the high side pressures that you have reported are reasonable and encouraging but are not worth much without knowing the consequent drop in the low side pressure and the ambient temperature.

 

A set of guages for less than £30 are a very good investment, I have left mine and my manuals in France so cannot comment on the readings but all the info is out there on the net, be aware that most is written for an EM coupling type compressor and your one being a constant drive modulated one works differently.

 

From memory mine in good working order would have 5 bar low & high side engine switched off at 20°c ambient, running the engine and putting the aircon on full cold high fan speed the high side would climb to 150psi and when the radiator fans cut in drop and stabilise to 100psi with the low side at about 3bar, sorry for mixing the units and they are all from memory so may not be spot on but the 150 and 100psi ones are as I wrote them down as being different to what most resources (for the clutch type compressors) say, when the charge was too low the fans did not cut in, do yours?

[J.R.]

9 bar would suggest they are not cutting in but VCDS reports the pressures differently to a manifold guage, I think VCDS is absolute pressure and the guage is well, - guage pressure as you would expect!!!

[dieselV6]

Thanks for replies, seems pressures are at least within the "should work somewhat" range

 

What puzzles me is that there seems no temperature drop after evaporator, it's basically temperature of incoming air - suggest airco not cooling at all, even on low fan settings. How's that even possible when there is refrigerant and it's pumped round?

 

I have just tried flap recalibration, compressor break-in procedure in basic settings, no result. 

I'm concerrned this is not a refrigerant problem but rather some sensor/wrong temperature readout problem, or some valve not switching, etc..

Makes no sense to do regas IMHO if the problem is elsewhere.

 

Anyone with VCDS/OBD11 who could check temperature after evaporator on their Mk3 ?

 

Fans are modulated, and at around 28% when VCDS read pressure is around 8-9bar. But the airco does not blow out cold air when the car is moving, either, so fans not an issue.

I also checked vent temp the old fashioned way, with a probe, never below intake air temp, even at "LO" setting, though as soon as I set "HI" temp, it rises to 40degC and above. So the temp flap is working

Edited 26 April, 2022 by dieselV6

[J.R.]

My suggestion is that you stop observing what is happening through a computer screen and use your real senses, a lot of what VCDS produces is utter rubbish, commanded or worse still theoretical values but with no closed loop feedback to know that the action is actually happening, fans at 28% being one of them, the power drawn by the compressor another.

 

You should look at the high side pressure (OK you need your screen for that) and watch the fans with your eyes, the pressure should climb and the fans should cut in after say 20-30 seconds at which point the pressure will fall and equalise & that is when the refrigeration occurs, it does not sound to me like your vehicle is doing this and in the absence of having proper high & low side guage readings plus ambient temperature my gut feeling is that you are low on refrigerant.

[dieselV6]

Well, I thought the whole point of overpaying for Skodas lately was that the extended sensors and internal diagnostics should be able to clearly indicate what is wrong 🙂

 

In any case, I rechecked high pressure side this morning before starting the car, it was 3 bar (2 bar relative) so looked like low on refrigenrant. 

By the way, even with refrigerant this low, the building up pressure from 5 bar to 9 bar and then the drop to 6.5 bar can be observed as you run the airco, yet it is not cooling at all.

 

Subsequently, I got a low pressure side gauge/trigger from local shop, confirmed low side to be below 10psi 🙄. Well, at least it was still above ambient pressure.

One 300g R1234yf topup later, everything is working fine, evaporator temp 0.7-2.3degC, vent temp around 6 deg C upper ones, 8 deg C footwells.

I have UV dye in the system now, so if it leaks (2nd topup in 6 years), there will be a chance to find out where.

 

Thanks for answers, just to make it clear, I would not have been asking all these questions about older refrigerant, as I have a gauge and even a leftover half-topup for R134a from previous 3 cars, but the fittings for R1234yf are different.

At the same time, a lot more info in VCDS for this car's HVAC, shame they have failed to include low side airco pressure sensor - I guess it would be most useful.

 

 

[dieselV6]

I found this useful table for anyone wanting to diagnose with VCDS (look at "refrigerant pressure"):
https://forums.ross-tech.com/index.php?threads/633/

 

So if you see <4 bar before you switch the engine on and the temp outside is 15deg C or above, the airco is low on refrigerant... Hope this helps the next person

G65 Pressure vs. Temperature chart
(When key is on, engine is off, static system pressure)

15C - 59F - 4.0 bar
20C - 68F - 5.0 bar
25C - 77F - 6.0 bar
30C - 86F - 7.0 bar
35C - 95F - 8.0 bar
40C - 104F - 9.0 bar

Important to note about the G65 sensor:
- A reading of 0.0 bar would indicate an absolute vacuum
- At Sea Level (atmospheric pressure) the typical reading is 1.0 bar