Thread: 2013 D4 Air Conditioner Issue

I’ve had a quote for $980 to replace valve by an Indy here in Adelaide. Anyone know someone here who can do it at a better price. I don’t have the wherewithal to do it myself.

Originally Posted by letherm

Mine is an HSE and I just set the desired temperature for passenger and driver via the dials either side of the console. Usually I just leave it on Auto and A/C and it does its own thing. To answer your question, I assume it is internally shut off as there is still cool air coming out of the vents. It was 41 outside and I had the temp set at 16 and then put it on 20 thinking the difference in temp might be outside its working range but it has handled heat before.

Martin

16 is very low and asking a lot of the system. Have you tried 24?

Originally Posted by DiscoMick

16 is very low and asking a lot of the system. Have you tried 24?

If its 41 outside there will be zero difference between 16 & 24. Either way the system will be running flat out to try and keep up.

If you want an idea as to how hard it'll be working, check out the system pressure, interior temperature and left/right solar loads on the IID.

Yeah should maybe aim for about 10 below the ambient temperature.
The climate control in our Mazda 2 seems happy set on 24.

Originally Posted by DiscoMick

16 is very low and asking a lot of the system. Have you tried 24?

I don't normally run it at 16 but was trying to see if it would get colder. I suppose on average I run at 20 to 22. My wife likes to live in a fridge so I acclimatised. That said, it's never been a problem before.

Martin

Originally Posted by BradC

If you want an idea as to how hard it'll be working, check out the system pressure, interior temperature and left/right solar loads on the IID.

What would be a normal reading? I did pull up some data but didn't know whether it was good or bad. From memory there was a pressure reading of around 1600.

Martin

Originally Posted by letherm

What would be a normal reading? I did pull up some data but didn't know whether it was good or bad. From memory there was a pressure reading of around 1600.

Martin

Ok, this started out as a quick pt post, but it has rapidly grown. Excuse the ramble.

"Normal" is relative. That pressure is the high side pressure of the system and is a direct measurement of the saturated condensing temperature.
This can be easily translated using a pt chart for r134a.
Pressures in kPA, Temp in C. Roughly rounded

900	39
1100	46
1300	53
1500	58
1700	63
1900	68

The condenser is designed roughly for a 10/15C split above ambient. So at design conditions on a 40C day you'd be expecting to see 50/55C saturated condensing temperature (SCT), or ~1200-1360kpa.
This is going to be at road speed with a large airflow over the condenser.
Sitting at traffic lights that will rise considerably, and at low cabin heat loads it'll fall.

At the same conditions, your evaporator temperature is going to target somewhere around ~2C. At traffic lights when the SCT is high and the compressor speed is low that will rise (I've seen 9C). Get the revs up a bit and it'll drop back down. When the airflow over the condenser increases it'll fall further.

The compressor is just a normal gas compressor. It takes gas at a low pressure and compresses it up to a higher pressure. It suffers the same losses as any other compressor with regards to valve efficiency, blowby and dead space in the head. So, the higher the output pressure, the lower the efficiency of the compressor.

That translates as the lower the SCT (head pressure) the more gas the compressor will move for the same displacement. So the system always works better at speed as you have a lower condensing temperature resulting in a lower head pressure.

The condenser serves 2 roles. It condenses the hot vapor into warm liquid, and it subcools that warm liquid below the condensing temperature. It does this because at the correct charge level there is enough liquid to both fill the evaporator and back up some liquid into the condenser. As the charge level falls, the amount of liquid in the condenser is reduced and therefore the degree of subcooling falls. When that reaches the point you start to feel it there is no subcooling and the liquid reaching the TXV is already starting to boil. That reduces the flow through the TXV and starves the evaporator of liquid, reducing its capacity.

You'll see that as an increased evaporator temperature, and a reduced high side pressure. As the evaporator extracts less heat from the air, the refrigerant has less heat to reject into the condenser. This'll result in a lower SCT as with less heat to reject the refrigerant is easier to condense.

That leads to the final element, which is oil flow. The compressor ejects oil in the discharge gas. It works its way through the condenser by gravity and condensing refrigerant droplets where it is carried by the subcooled liquid into the evaporator. In a properly charged system the refrigerant in the evaporator is violently boiling such that at the evaporator exit there is a superheated vapor of refrigerant and entrained oil leaving. As the charge level falls, the boiling moves down from the top of the evaporator. This reduces the amount of oil ejected from the top of the evaporator (as it has time to start to fall out of suspension before it leaves) and so more oil stays trapped in the evaporator rather than making its way back to the compressor. The compressor ends up getting starved of oil resulting in mechanical damage.

Back to the condenser. As it performs 2 roles (condensing and subcooling) there is a balance between these roles, and the specified refrigerant volume (weight) is designed to hit the right balance as determined by the manufacturer. When you charge a system there are 2 ways to do it :
- By weight. Pull all the gas out (weigh it to see how much was left) and put the right qty back in.
- By subcooling. Get the system running at design parameters, measure the high side pressure and liquid temperature leaving the condenser, and adjust the charge until you have the correct subcooling level. For this you need the design parameters and correct figures to go by.

Too much gas and you raise the SCT so the compressor has to work harder. Too little gas and you lower the subcooling which will affect the TXV and cause reduced evaporator capacity.
This is why everyone does it by weight. It's the easiest method to know you have it right.

Sorry, that got a bit longer than I had intended.

geoffx19 found this link online, specifically related to the valve issue and there is now a part number for it.

https://testing-public.carmd.com/Tsb...5/LTB00693NAS1