maxandtara

I have a 2005 a8 d3 v8

I am not satisfied with the cooling performance of my car. Comfort is relative, I do recall my car’s A/C ran a lot better than this some time before.

VCDS = no errors
reading show hvac is running efficiently

Car R134a psi readings Low = 30 H = 180


This first website I came across states psi reading for my A/C is about normal.

At 90F L = 30 H = 230 ( I am no expert H side a little low maybe ?)

It is the Houston Summer. I want my A/C to run COLD!
I did a little more research and picked a chart with that was easy to read and had the most common Ambient temp to PSI readings out there.
(see chart below)



Based on this chart here are my conclusions:

Low pressure

• Cooler temp 65-80F (Max psi changes 1 psi per 1 degree F) (35-50 psi range)
• Warmer temp 85-110F ( Max psi 55)

High pressure

• 65-110F psi range consistently increases as temp increases

According to my phone Houston temp is at 90F. Based on this chart my car is low on refrigerant.

90F L = 45-55 H = 250-270 Actual at 90F L = 30 H=180

There is a lot of talk about adding the exact amount of refrigerant.
The best procedure is to evacuate the system and then add r134a I agree.
I also agree that adding too much refrigerant is not good.
(I have seen this happen. Too much refrigerant will decrease performance.)
Most of us reading these posts prefer to do stuff ourselves.
Since I am not happy with the temp. Adding refrigerant is the better option than status quo.
If this does not work, I may have to replace parts therefore must evacuate the system anyway.

Concerns:

• Overcharging will destroy the A/C.
• Flooding the A/C with refrigerant will destroy the compressor

Since
-VCDS says hvac is normal.
-Low and Hi pressure reading indicate low refrigerant.
-I have the proper tools and supplies( manifold gauge, tapping tool 12oz can of r134a).

Lets give this a shot!


My process.

1. Check manifold reading are at zero.
2. Check Dials on manifold are at closed position (clockwise).
3. My connectors are manual. Turn counter clockwise so as not to engage the schrader valves.
4. Attach connectors to low and high side (car is off). One more way to check gauges are working properly.

5. Turn Low side Clockwise until the gauges move .

6. Turn High side Clockwise until the gauges move . (Some say turning the connectors at max may destroy schrader valves)

7. Pressures should be the same because A/C is not running mine read 65 psi on the low and the high side .

8. Start Car. Open all windows. Turn on A/C to lowest setting (LO) I came from the office so I did not have to warm up the car.

9. Take note of readings. My reading L=30 H=180 according to the chart, refrigerant level is low. Therefore, I need to add R134a.



10. Confirm tap connector is turned counterclockwise (pin is up) and attached to middle yellow hose.

11. Attach refrigerant can to the tap connector.

12. Puncture can by turning valve clockwise. Turn counterclockwise to release r134a to the line. Bleed air in the line by releasing some refrigerant. Depress the middle valve on the manifold 2 to 3 sec.

13. Refrigerant can upside down. Open LOW pressure (counterclockwise) until psi hits 75 for 2 to 3 secs then close. Wait roughly 3 minutes. (I did this to avoid flooding the compressor with too much r134a [play it safe])

14. Kept on repeating step 11 above multiple times until I reach target pressures.

• To be on the safe side (avoid over pressurization) though ambient temp is 90F I will use the 85F range to add another layer of precaution.
• According to the chart at 85F L = 45 to 55psi H = 225 to 250psi

Observations while adding R134a
Sight glass shows liquid refrigerant
Initially, Low side psi went up faster relative to the high side.
Suspected something wrong because the gauges barely changed after each squirt of r134a.
So, don’t worry, go through the motions. I am no expert but I think this is normal.
Low side PSI came close to 53 PSI but settled to 50 PSI
High side PSI maxed out at 230 PSI

Stopping point :

I stopped because I ran out of refrigerant.
I using the smaller cans is safer for us non-professionals.

Target L = 53-54 (max 55) H = 240-245 (max 250)
Actual L = 50-51 H = 231 (close)

• One site said that I had enough r134a (initially).
• I added 12 ounces of refrigerant
• Specifications of A8 is at 21 ounces. I believe it is best to stop here and test the car before adding more.

15 When done, Check low side dial is in the closed position (clockwise).

16 Turn Connectors off (counterclockwise). Detach connectors.

17. Turn off Car.

Drove my car to work the following day. I usually have the settings at 68F. I had to turn it up to 72F. I think I am good.
For my case simply adding refrigerant was a good decision.

Lessons:

Don’t be afraid to work on your car.
Have some basic understanding of how your car works.
Have the proper tools.
Use common sense.
When you decide to take the plunge dot your I’s and cross your t’s. (putting a plan in place to avoid over pressurization and flooding compressor with refrigerant)
You need to be reading both High and Low side PSI when you are adding r134a.

I hope this helps somebody out there

Dart

PaulW

Awesome write up and I agree with how you did it. I think you could of also done that with an AC pro gauge/hose and a 375 ml of refrigerant. Takes a few minutes.

Thanks for posting!

maxandtara

Paul

Thanks for the compliment.

Ideally, I would have preferred evacuating the system first and then put refrigerant.

In fact I already bought some parts, I would have done it like the way Louise has done it to his car

I think like you we have added refrigerant to our cars multiple times through the years.

Simply adding the refrigerant is not the main concern but adding it properly as a DIY non-professional A/C technician.

I wanted to do it in such a way I ha a high level of confidence I was doing it right. I wanted to be sure, I was not making the situation worse.

If things did not pan out the way it did, I would have narrowed down the issues of the hvac.

For example. You are right that you can use a AC pro gauge/hose and see some low pressure reading that gives you indication that the refrigerant is bringing the low pressure side to spec.
To be able to see the high pressure side gives confirmation that the added refrigerant is allowing the system to come closer to spec
Being able to the same system using different perspectives (VCDS, Low pressure, & High pressure.) was my goal.