[Gannu_1]

I recharged the refrigerant in my Polo’s AC system some time back. The AC’s cooling effect in my car had noticeably reduced and I could feel it during my daily drives. I began hearing a strange hissing noise from the vents which wasn’t there before. I decided to read up more on this, how the refrigerant on car’s AC systems are recharged and figured out that if the system is running low on refrigerant and there are no other issues with the other components of the system, topping it up is pretty simple and restores the cooling performance. Putting up a dedicated, detailed DIY thread to our repository for reference.

Disclaimer:

I am not an HVAC expert and whatever I did was purely for the learning and experience.

Background:

When the issue cropped up, I did a quick check on all the related components of the HVAC system:

1. Compressor - turns on when I press the AC button and I could hear a distinctive ‘click’ from the relay. Upon physical inspection, there were no issues with the drive belt driving the compressor. It was also replaced during the timing belt service. No other noise related to the pulley or bearing.
   
   
2. Evaporator - assumed to be working fine. I did not see any water collected in the footwell or a clogged drain outlet. No visible frosting observed when viewed from the cabin air filter cavity.
   
   
3. Condenser - assumed to be working fine. The fins were not clogged or dirtier than usual. I use the compressed air from these service centres and garages to clean the fins. Never did an alkali cleaning though.
   
   
4. Expansion valve - assumed to be working fine. The expansion valve is installed outside the firewall/plenum chamber bulkhead.
   
   
5. Blower - works fine. Spins at different speeds depending on the setting so the blower resistor had no complaints either.
   
   
6. Dust and pollen filter - relatively clean. It was changed during the last service 5 months back and the recirculation mode is set to ON at all times so the car doesn’t draw fresh air from outside and therefore does not contaminate the filter quickly.

The last thing left to check was the refrigerant in the system.

The lack of refrigerant in the system can result in ineffective cooling. Despite being completely sealed systems, refrigerant levels drop over time as the rubber seals/o-rings in the connectors of the rubber hoses and metal tubes wear out and causes the refrigerant to gradually leak out over time. If there is a puncture in the metal tubes or hoses, or the condenser coil due to a nasty stone hit, the refrigerant would again leak out. Sometimes, gas leaks out from the schrader valves present in the charging ports of the car in extremely minor quantities. But if the car is over 6-8 years old and the AC’s cooling effect has reduced over time, there’s a good chance this is due to the lack of refrigerant in the system; as it turned out to be in my case. Over all these years, I have never had an AC refrigerant recharge. But at this stage, I do not know if there are any leaks in the system.

Tools required:

1. AC manifold setup
   
   
   
   
2. Probe thermometer or the one in your digital multimeter (DMM) if you have the option
   
   
   

Consumables required:

• R-134a refrigerant can - 450g (costs Rs 430 for a can; sufficient for a hatchback)
  
  
  
  The type of refrigerant used in the car and and the quantity is indicated in a sticker stuck on the engine bay or on the hood.
  
  

PPE required:

1. Safety goggles
   
   
2. Nitrile gloves

The AC manifold setup:

The AC manifold setup is used to recharge or evacuate the refrigerant from the system and measure the pressures at the low-pressure (LP) and high-pressure (HP) lines. It has a brass manifold with 2 pressure gauges - one for the low pressure side marked in blue (marked from 0 - 220 psi) and the other for the high pressure side marked in red (marked from 0 - 500 psi).



There is a valve mounted on either side which controls the flow of refrigerant through the 3 threaded ports on the manifold. While charging the refrigerant, the valve next to the LP side is opened and the refrigerant flows from the refrigerant can (stored under high pressure just like your LPG cylinder) to the system (low pressure side) in the liquid phase. The manifold has a gauge glass at the centre which shows the flow of refrigerant while charging the setup.



Color coded hoses are used to connect the manifold to the system. Just like the pressure gauges, blue for the LP side, red for the HP side and yellow for charging or evacuating. Color codes are for easy identification - otherwise the hoses are identical in terms of connectors and size.



These hoses have threaded schrader valves at the ends just like the ones in the tyres. Press the central pin and the gas escapes.



To connect the hoses to the car’s LP and HP ports, quick coupler fittings are provided. These are also color coded - blue for the LP side and red for the HP side.



The quick couplers are foolproof because the openings are different. The LP quick coupler has a smaller opening while the HP one has a larger opening. One cannot fit the wrong fitting to the port.



These quick couplers snap onto the charging ports in the car, just like the LPG gas cylinder regulators we have at home.



While charging the system, the yellow hose connects to the refrigerant can using a threaded valve. The valve has a pointy end:



Screw the valve in the clockwise direction and it pierces the can, open the valve in the counterclockwise direction and the refrigerant escapes out. Take extra care to ensure the valve is opened before screwing it to the can; otherwise, it’ll pierce the can and refrigerant would leak out!

While recovering the refrigerant or pulling a vacuum on the system, the yellow hose is connected to a recovery unit or vacuum pump respectively. Changing the compressor/condenser coil/evaporator coil/leaking hoses or tubes demands evacuating the refrigerant from the system.


(Source: Google Images)

The manifold has dummy threaded ports at the back...:



...to park the hoses when not being used. This will prevent dirt and dust from entering into the hoses.



I sourced the complete manifold kit with the hoses and quick connectors from a neighbourhood car AC parts store and cost me Rs. 2300. The good thing was unlike buying online, I could physically check the parts and their quality. Plus, the shop also agreed to replace a part if there was any leak but no other guarantee otherwise. Plus, the same setup can be used to charge the refrigerant in a home AC unit with the right refrigerant; not that I intend to for now but good to know this can be done with the same kit.

Procedure:

• Start the engine, set the temperature to the lowest setting, blower to the highest speed and measure the temperature of the air from the vents using the probe thermometer for reference. I’ve used the one on my DMM.





As you can see, the air is not chilled enough.

• Pop up the hood and hang the AC manifold setup. Ensure that both the valves are closed. Hang the ref. can and screw the valve to the can (ensure the valve is open!).



• Find the LP and HP service ports from the AC system in your car.

LP port - smaller port on a larger pipe
HP port - larger port on a smaller pipe.



Remove the dust caps from the ports. Keep the dust caps secure.



• Connect the LP/blue quick coupler fitting to the LP port and the HP/red quick coupler fitting to the HP port. Take care to ensure that the quick couplers are closed while connecting them.



• Gently open the valves on the quick couplers and the reading would show up on both the pressure gauges. There is no need to open the valves on the quick couplers completely. Once the gauges show the reading, that’s sufficient.



On that note, even if the valves on the manifold unit are closed, the readings will show up on the gauges as these valves control the flow of refrigerant from the centre port to the LP or HP ports.

• Have a partner start the engine, rev it to 1500 rpm and check the pressure readings on both the gauges. At higher engine speeds (like in real life situations when the car is in motion), the compressor's pulley would be spinning properly and this would give a proper reading on the gauges.



Measure the ambient temperature and compare the reading with the pressure-temperature chart of R134a below:



In my case, the ambient temperature was around 28°C.



Corresponding to this temperature, the LP gauge should read between 45 - 50 psi and the HP gauge should read between 190 - 230 psi from the reference chart. The LP gauge reading is okay but as evident from the HP gauge, the reading is 135 psi which is low and indicates the HP/discharge side does not have sufficient refrigerant flow.

• Wear the safety googles and a pair of nitrile gloves before working on the ref. can as direct contact with the refrigerant can result in frostbite.



• Screw down the valve on the ref. can completely to puncture it and turn it back in the opposite direction to let the refrigerant flow through the yellow hose to the manifold unit.



The yellow tube now has a combination of ambient air + refrigerant. Air/moisture is not good for the system and must be purged from the line before charging. Gently unscrew the connector of the yellow hose at the manifold end to purge the air from the hose until some refrigerant comes out.



Screw the connector back firmly.

• Gently open the LP side valve on the manifold unit to charge the system with the refrigerant.



You will notice the flow of refrigerant in the liquid phase through the gauge glass on the manifold:



Close the valve. All the refrigerant from the can should not be charged into the system at once!

• Notice the reading on both the gauges. The reading on the HP gauge (discharge side) should begin rising gradually as the refrigerant is being charged into the system.



• For the measured ambient temperature (28°C), find out till what value should the HP gauge needle should climb from the R134a temperature pressure reference chart. It should be between 190 - 230 psi. Open the LP valve to charge the refrigerant in short intervals so the HP gauge needle climbs up to this value and stop.



Additional refrigerant does more harm than good - affects cooling performance, can damage the compressor, valves and the seals. Please be careful not to open the LP valve completely in one go!

• Check the temperature from the probe thermometer inside the cabin. It should now read a lower temperature suggesting that the charging process went properly.



If you still have issues, you may want to visit a good car AC service garage/technician - unlike other car garages, these guys can quickly diagnose an issue related to the AC system and suggest a proper course of action for a shorter turnaround time and expense. I could have done this too but preferred to do this on my own just to know the process and learn from it.

• For those who prefer a video tutorial, here it is:

https://www.youtube.com/watch?v=ZV30LNeCcKs

Thanks for reading guys. Trust this was useful. Let me know if you have any comments or feedback or if I've erred in my assessment somewhere.

PS: If you're interested, there's a very handy training manual that I got off the internet about car AC systems which is attached below.

[GTO]

Thread moved from the Assembly Line to the DIY section. Thanks for sharing!

Going to our homepage today . Good to have Gannu back in the DIY section .

[hserus]

Nice diy but don't be surprised if the AC gas level goes down again within the next few weeks.

The aircon is a sealed system and gas will not escape in a well functioning AC. Check the car's evaporator / cooling coil for dust clogging, then check your AC filter which I hope you are cleaning if not replacing every 5k (if you clean replace it at the 10k mark, regardless of what your car's manual says).

[sagarpadaki]

Originally Posted by hserus

Nice diy but don't be surprised if the AC gas level goes down again within the next few weeks.

The aircon is a sealed system and gas will not escape in a well functioning AC. Check the car's evaporator / cooling coil for dust clogging, then check your AC filter which I hope you are cleaning if not replacing every 5k (if you clean replace it at the 10k mark, regardless of what your car's manual says).

That depends. In my case, the cooling dropped one fine day 9 years into the ownership and the cause was low refrigerant. Maybe the refrigerant was leaking gradually and one day it dropped below the threshold and the cooling dropped. When checked for leaks, there was not leaks since the vacuum held for almost 1.5 hrs. After it was refilled with fresh refrigerant, no issues for the past 3 years

[Pulse500]

Originally Posted by hserus

Nice diy but don't be surprised if the AC gas level goes down again within the next few weeks.

The aircon is a sealed system and gas will not escape in a well functioning AC. Check the car's evaporator / cooling coil for dust clogging, then check your AC filter which I hope you are cleaning if not replacing every 5k (if you clean replace it at the 10k mark, regardless of what your car's manual says).

I faced different issues on different occasions that resulted in refrigerant escaping out.

Once there was a damaged hose connecting the AC condenser that leaked out the refrigerant within a few seconds. This needed replacement of hose, gaskets/seals etc, fresh compressor oil and refrigerant through a trained professional at a workshop.

Second time, slow leakage was suspected due to defective AC evaporator (took 8-9 months for refrigerant to leak out). Even after replacing the evaporator, hoses, gaskets etc and keeping vacuum for ~3 days that suggested no leakage, some refrigerant still used to escape especially driving on rough roads. The evaporator assembly replacement was done at Mahindra authorized service center.

Driving on rough roads still results in slow leakage of refrigerant. There are no compressor oil traces visible anywhere even after the refrigerant leaks, which surprised me.

I have used DIY method twice to top up the refrigerant, first time in summer 2016 (consumed nearly one full 400gm can, the total capacity of the XUV system is mentioned as ~800gm), and once in Oct'21 (used nearly 350 gm).

I also did DIY on my Accent Viva CRDi, which had cooling performance degradation after nearly 10 years of use.

In all the cases, I did ensure prior cleaning/replacement of cabin AC filters, inspection to find traces of oil, clean external condenser (water spray using garden hose) before attempting DIY topping up refrigerant.

So I conclude that due to possible design issues (especially newly launched cars), inappropriate handling of parts during assembly or repairs of vehicle, worn out gaskets, defective parts or for some other reasons, the AC system, even if is fully sealed, still may have some minor slow leaks.

[ynot]

Depending on the amount of gas that needed charging, it may need a bit of oil in there. Sometimes loss of cooling can also be a faulty expansion valve or clogged receiver dryer. Good to see the tutorial of how its done.

[sukarsan]

I had posted (Understanding Car Air-Conditioners) a query couple of years ago on what should be the pressure for AC gas verification. I was thinking 350 psi/25 bar was a high value and was of the opinion that maybe the AC mechanic was intentionally creating a damaged coil. But now i see that its a legit value.

Great post.. Thanks for clearing my query!

[hserus]

At least with Mahindra I've experienced slow leaks caused by slightly damaged cooling coils (you can see spots of an oil leak in the coil as the damage increases and cooling power gradually drops off), sometime around the 5 year mark, in two scorpios so far.

Filling gas and checking how long it takes to leak out is certainly a way to go, as any AC repair will involve disassembling the dashboard for most cars. But audible clues to a leak exist as well, such as a slight hissing noise from the aircon vent, a gradual decrease in AC throw and maybe also a stuffy smell in the car caused by the refrigerant gas also coming in along with the air from the ac vents.

If you see unexplained slow leaks a test where some dye is mixed in with the ac gas and injected in, then you check for the presence of the dye outside the ac system is a good one to do. Check this video for example (and the comments are, for once in a youtube video, insightful).

https://www.youtube.com/watch?v=kZiQGWz7Ka0

Originally Posted by Pulse500

Second time, slow leakage was suspected due to defective AC evaporator (took 8-9 months for refrigerant to leak out). Even after replacing the evaporator, hoses, gaskets etc and keeping vacuum for ~3 days that suggested no leakage, some refrigerant still used to escape especially driving on rough roads. The evaporator assembly replacement was done at Mahindra authorized service center.

Driving on rough roads still results in slow leakage of refrigerant. There are no compressor oil traces visible anywhere even after the refrigerant leaks, which surprised me.
.

[sandeepmohan]

Thanks.

I want to add that this isn't a DIY for everyone. The equipment used here is pretty much what any aircon technician uses so you need to be clear and know what it is for before you venture into this. If you are okay with some trial and error, then all good. Any air conditioning system is complex. If there is a leak or technical glitch anywhere, you'll likely be pulling your hair out.

A system leak is easier to diagnose for a home aircon system versus a car where much of the plumbing is out of sight or hard to reach.

I had attempted this a couple of times for my Blue Star home aircon when I had to relocate twice and once for my wife's Mercedes A170. The process I followed for the car was easier and simpler. I'd say some luck played in my favor too as the system was low on refrigerant. Had there been a leak, a need to evacuate the system, I doubt if I would have ever attempted to fix it by myself. I also had a refrigerant top up solution like this CRC, which made the process a lot simpler.

For my home aircon, I had my uncle on hand for help, who is well versed with this stuff (Quite like you Gannu). He installed his brand new Samsung aircon as he wanted a perfect installation, meaning correct evacuation of the system before charging the system or releasing gas from the outdoor unit (They come pre charged these days). As a result, I got to learn a lot about the process.

The car was a simple and interesting process. Now that you've shared the ideal pressure values chart, it does look like I charged the system to the right level based on ambient temperature. We bought this car used and from the day we took delivery, I noticed the aircon was not quite up to it. When summer arrived, it was not blowing cold air unless the fan level was on 1, which was too low for effective cooling of the cabin. Once more air started passing through the evaporator (higher fan speed), the system did not have enough refrigerant to cool the exchanged air passing through. It was cool air, not cold. The car had a warranty and we needed to drive almost 15km back to the dealer to have them attend to it. I thought, why not attempt a DIY and if that did not work, we go to the dealer. I bought a CRC Refrigerant (link above) top up can and refill apparatus for $70. The refill can and gauge/apparatus are sold separate. The refill apparatus is a little trigger gun that releases refrigerant.

• You start by first hooking up the gauge/refill apparatus to the low pressure line (marked L) to check how much refrigerant there is in the system. When I checked, there was less than 10 psi.
  
• Cranked the car, air con engaged with the fan at maximum speed and temperature setting at its lowest (or coldest).
  
• Attach refill apparatus to refrigerant can. Its a simple screw on process.
  
• Snap the hose to the low pressure line. Squeeze trigger to release refrigerant. Swivel the can between the 12pm and 3pm every few seconds. Release trigger after 10 seconds and check psi levels. I followed the color codes on the gauge as that's all I knew. I stopped when it reached the 30 psi mark. The can was almost empty by this time.
  
• While gradually introducing refrigerant into the system, I noticed the radiator fan spin up to its highest speed. Had not observed this before. This can vary from vehicle to vehicle. Some have fixed speed fans. This was not to cool the engine. It was to push more heat out of the condenser. A sign that the system was working. I started to notice moisture deposits on the aluminum aircon lines too.
  
• Went into the car to check and the cabin was cold just minutes into this process.

Its over 2 years now since the refill and the system has held up. I have not checked the level again as the system is cooling as it should. In the end, was pleased that I took the DIY route before heading to the dealer. Saved a lot of time in the process.

On a side note, for some cars, reaching the low and high pressures lines are easy. For some, they are not. You'll need to look around or pull a schematic for your car to find the lines. Cars with smaller engines tend to have more working room too. My previous car, a Fiat Linea had the low pressure line deep behind the engine and close to the compressor which was near the firewall. Had to bend deep down to reach the nozzle. The high pressure access location was right in front, beside the headlamp.

[hserus]

One of those machines that evacuates all refrigerant from the system, pumps it back and then tops up the exact amount is ideal for this work. You don't deal in approximations that way, and all the air that may have bled into the system due to low pressure is also pumped out.

Originally Posted by sandeepmohan

Thanks.
I want to add that this isn't a DIY for everyone. The equipment used here is pretty much what any aircon technician uses so you need to be clear and know what it is for before you venture into this. If you are okay with some trial and error, then all good. Any air conditioning system is complex. If there is a leak or technical glitch anywhere, you'll likely be pulling your hair out.

[RGK]

Originally Posted by Gannu_1

• Check the temperature from the probe thermometer inside the cabin. It should now read a lower temperature suggesting that the charging process went properly.

Thanks for the DIY Gannu saab, but this is not a simple activity to be done. One need to be technically competent to take up this kind of work at home.

What was the final temperature shown by the gauge after the refill?.

There is one highly skilled AC technician (Guru) in East CIT Nagar (Backside of the Nexa Showroom, Nandanam, Chennai) who does service for all cars. He diagnoses the AC performance by holding the aluminium pipe and recommends if the refill is required or not. His recommendation is to use the AC daily and clean the filter periodically for better performance.

[Gannu_1]

Originally Posted by hserus

Nice diy but don't be surprised if the AC gas level goes down again within the next few weeks.

It has held up well so far. The recharge was done during Jan first week and the AC is chilling now.

Originally Posted by RGK

What was the final temperature shown by the gauge after the refill?.

As shown towards the end of the clip, the temperatures began dropping after the recharge and it went up to 6°C. This was today morn when the temperature from the climatronic panel was set to 22°C:

[RGK]

Originally Posted by Gannu_1

As shown towards the end of the clip, the temperatures began dropping after the recharge and it went up to 6°C.

. The AC technician in the Ford ASC told that the temperature should be a maximum of 7°C at the lowest fan speed.

The gas level goes down when there is a tube leak or the oil seals/o rings are worn out without much AC usage.

[hserus]

Originally Posted by Gannu_1

It has held up well so far. The recharge was done during Jan first week and the AC is chilling now.

Has the throw improved from before you refilled it?

[Gannu_1]

Originally Posted by hserus

Has the throw improved from before you refilled it?

No the throw of air is the same; just the temperature dipped.

I change the cabin filter every 6-8 months now since they are dirt cheap. Have to remove the blower and do a proper cleaning now; have never done this activity so far.