[joybhowmik]

Originally Posted by SS-Traveller

Nice article there, Joy, with lots of obvious homework done in connivance with Google!

Thanks for all the positive comments SST. I don't necessarily view Google as a bad thing... I am sure you would agree that you too would not like a world bereft of a good search engine.
Having said that, it's up to the person, how he wishes to use the information. If you find there is something factually incorrect do let me know. Do provide me what needs to be the correction.

Originally Posted by joybhowmik

The most common cause of AC failure is leakage of the refrigerant through cracks, pinholes or other leak points.

and your repartee...

Not really. The most common complaint in car AC systems is loss of cooling, which is equally commonly traced to a choked cooling coil under the dashboard - something like this...

Now Webster defines failure as :

1b) : a situation or occurrence in which something does not work as it should

The word failure used in my post referred to a complete loss of desired functionality.

My view is the word complaint as used by you does not necessarily imply a failure.
That said, I agree - a choked cooling coil will cause delayed cooling- yes and one may conceivably argue - that's not desired functionality either.
But it will not result in AC failure - as in, the AC will still work, one will eventually get to the desired temperature but one has to sweat for 10 minutes more (in a manner of speaking).

That said, I agree the chief cause of customer complaint is a choked cooling coil.
And that is why I have recommended that it may be appropriate to have the AC serviced once every 2 years or 24K km

Opening up and flushing a closed loop factory-sealed system every 2 years as a preventive measure? Not for me, thanks.

A very surprising comment. Surely that was in jest?

Do consider the rather dusty conditions in some parts of the country, including where we both live. I am sure you have experienced this given your car has been through most of the country by now - that the cabin filter (if there is one) , and evaporator (cooling coil) pick up dust on their surface from inside the cabin. How does it get there?
From our footwear, then on to the mat, and then pulled in by the suction in the footwell. The condenser is next to the radiator, and usually facing outside. One can well imagine the amount of dust/grime that gets on the surface after a while.
Now in an AC service, one of the most important jobs the mechanic does is - take out the condenser and evaporator and give it a thorough exterior wash. Washing off the grime and dirt that has accumulated on the condenser , is probably a good thing for the next few hundred km, but it does drastically improve the cooling efficiency of the evaporator for several thousand km (unless of course one persists in walking in and out of the car with muddy shoes on).

They can't very well do that without first draining the system of refrigerant. In case of roadside mechanics - they drain by just letting the refrigerant escape out into the air. In company A.S.S. workshops , (where there is a fear of environmental watch dogs), they recover the refrigerant in a slightly more civilized way, and recycle it. Then they create a vaccuum, before recharging the system. They will flush the lines on request , because sometimes, especially with a tired receiver/drier, small quantities of fluoric / hydrochloric acid forms as a result of retained moisture combining with the r134 (or variant) in the closed loop system, which in turn causes some corrosion in the lines - and effectively leads to a build-up of obstructive material.

Whose side are you on, anyway?

Again, its up to personal preference. One can pay for a complete service costing between 1.5 K to 6K (prices not valid for expensive supercars or bmw's or their genre ) once every 2 years.
Or one can do nothing but just sell the car after 5 years, and wash the problem off one's hands. To each his poison.

You didn't add cost as a reason.

Thanks. Yes cost is another reason. I wish someone in the moderator team can add this point to the main post. I unfortunately am unable. The UV test involves specialized equipment - primarily some injectable dye and a special UV light to shine on the plumbing. And that is not something you will find at the roadside mechanic. But you may find it at the A.S.S.
In fact, in Toyota's A.S.S. they have it. But one has to ask for the test to be performed as part of service, if one suspects a leak (no refrigerant left).

Replace what? The whole plumbing?

I have shown a picture of expected spots where leaks can occur.

If it is the condenser or evaporator - and rust has caused leak points, one can get away with a refurbishment. Typically A.S.S. will not do this - they will only replace. That's why, if one has a leaking condenser (perforated coil), or an evaporator, take it to the roadside mechanic , who will get it brazed at a specialist shop.
If on the other hand , it's a hose, or a joint, or a seal - get it replaced. Just for peace of mind. I am quite sure there's no returns in exchanging pennies now for a failure later.

Any comment about what kind of compressor has what advantage / disadvantage?

Fixed displacement, Swash plate compressors offer higher durability.smaller size , lower weight, lower NVH, higher efficiency

Variable displacement compressors provide the ability to give varying compression at different speeds, thus controlling the degree of refrigeration. This has the added benefit of improving clutch life.

Screw/Scroll compressors (types of rotary compressors) offer lower NVH, high efficiency, low maintenance.

Which automobile makers use what type of compressor?

Many automakers today prefer the swash plate type of compressor- e.g. Honda, Toyota. But others, e.g. Ford have not taken sides one way or another.

And how (if at all) are car AC compressors different from home AC compressors?

Different applications. And different drives. Two points.
1) To put it simply, a car AC compressor's only power input is the rotation of the pulley, whose speed depends on engine rpm (a variable factor). Hence,the way to control the degree of refrigeration , has taken on increasing complexity. Now we have variable displacement compressors, swash plate compressors et al. These have evolved due to the different needs and expectations from an auto compressor:
e.g. low nvh, high efficiency, higher performance, less weight, small size , more durability, less maintenance requirement etc.

This kind of complexity is not needed in homes, where the primary energy input is a hopefully constant voltage. Which means , that a thermostat is all that is required to maintain temperature. Also, there's usually no one bothered about weight of the compressor in a home application , or its size.

2) The other big difference is the space required to be cooled. Home spaces are much larger, requiring much larger displacement in the compressor to keep up with the heat energy entering the room. In cars the enclosed space is much smaller. Further, the larger the compressor in the car the lesser the fuel economy, and the more the weight. So, in auto applications, reaching the right temperature quickly is important, but equally in many countries, it's equally important to be frugal. So heavy duty large displacement auto compressors that consume a lot of energy , have fallen out of favour.

I'm appalled, Joy. All this homework, and then you tell our readers not to use this thread to get answers to their cars' AC issues? In which case the thread title of My Car A/C is not working. What to do? is entirely misleading!

I had meant this to be more of an article rather than a thread. A kind of reference if you will. So it's important that tidbits of usable information make their way into this thread. Not for more questions, and untested answers. There are enough threads meeting that requirement, and I thought it might help if this thread is relatively clean, which would make it easier to find information in it.

[mohan41]

Thanks Joy for this article. I found it quite useful as I had no knowledge of the working of any AC.

Few questions:

- We have this temperature knob in cars without Auto Climate Control which has green at one extreme and red and other extreme. If I set this to somewhere in between the two extremes to reduce the cooling, does it actually try to maintain a higher vent temperature (which I believe should reduce the load on the compressor) or does it mix some hot air with the cold air (that is what exactly one SA at a Hyundai A.S.S had told me)

- Some people say that frequently turning on/off AC causes damage to compressor. Is this true? If this is true, I cannot really switch off the engine when the car is stopped at traffic lights for long time (> 60 sec).

[joybhowmik]

Originally Posted by mohan41

- We have this temperature knob in cars without Auto Climate Control which has green at one extreme and red and other extreme. If I set this to somewhere in between the two extremes to reduce the cooling, does it actually try to maintain a higher vent temperature (which I believe should reduce the load on the compressor) or does it mix some hot air with the cold air (that is what exactly one SA at a Hyundai A.S.S had told me)

Your SA is quite right. The way this works, is that the hot air is mixed with the cold air. Here is the relevant specification for the Santro HVAC...obtained from the Hyundai service manual.

Heater unit
Type: Three-way-flow full-air-mix system

- Some people say that frequently turning on/off AC cause damage to compressor. Is this true? If this is true, I cannot really switch off the engine when the car is stopped at traffic lights for long time (> 60 sec).

OT: The benefit of switching off the engine at traffic lights itself is questionable.
Coming to the point.
When one is idling at the traffic light , the compressor is working at minimum rpm. Other than a slightly reduced fuel economy there's not much else that can go wrong.
But yes, frequent switching of the AC system, will cause the AC switch, AC relay and compressor clutch to overwork. More often than not, it will lead to a failed AC swith and/or relay, long long before the clutch itself needs to be overhauled. IMO, it will not really damage the compressor.

[ynot]

Remember to keep your condenser & radiator clean on the outside too. They work as heat exchangers and if the outside is dirty/clogged, you reduce your vehicle's potential to keep the engine and inside of your car cool.

Keeping the air circulation knob to recirculate will help cool the cabin faster and prevent dust and debris from entering into the car and collecting on the cooling coil (unless u have a filter and then that gets clogged)

[VeyronSuperSprt]

Some tips:

1. It is possible that in recirculation mode, you might find yourself feeling drowsy / or notice a lack of concentration. This drowsiness would be due to the stale air inside the car. Switch the A/c to Fresh air mode and you will feel alert almost immediately. If you have a high level of drowsiness, then additionally lowering the windows will make you feel alert fairly quickly.

2. If the engine overheats, the A/c system will shut down automatically in most cars. This is not a fault of the system but just to ensure that your interiors are also equally heated.

3. Flushing the A/c system every 2 years or 24,000 kms is certainly not advisable. If it were a recommended service measure, it would be specified in the service schedules just like any other regular maintenance. Tampering with manufacturer settings when not specifically recommended and in the absence of a fault can turn out to be harmful in the long run.

[roy_libran]

Thanks a ton, Joy, for collating this information together, and presenting it in a very comprehensive manner for commoner blokes like me.
I am now much better prepared to understand what the AC-wallah is really doing, and challenge him to do a job properly. For me, that is important.
Rated a well deserved 5 Stars.

[joybhowmik]

Originally Posted by joybhowmik

Refrigerant:
Usually described by the generic name "freon" the refrigerant gas is provided in pressurized containers and is usually a derivative of a haloalkaline refrigerant named 1,1,1,2-Tetrafluoroethane or R134A.

And here is an example of a refrigerant recovery and charging system.
Manufacturer : ATS ELGI

This system automatically recovers Refrigerant, build a vaccuum and holds it for a pre-programmed time, and recharges refrigerant mixed with compressor oil.
This is available at many metro main dealers, and used to safely recover and recharge the AC system with minimal impact on the environment.

[ramzsys]

Originally Posted by joybhowmik

The way this works, is that the hot air is mixed with the cold air.

Won't this cause the compressor to work for a longer time? Or is it the other way, the coldest setting puts the maximum load on the compressor?

[joybhowmik]

Originally Posted by ramzsys

Won't this cause the compressor to work for a longer time? Or is it the other way, the coldest setting puts the maximum load on the compressor?

The compressor starts working the moment the A/C switch is turned on (the center switch marked as A/C)


Behind the Hyundai Santro's dashboard are separate heater and evaporator units - as shown here (Picture courtesy: Hyundai Santro Service Manual)


The temperature control slider just controls the mix of hot air/cold air using control cables. Essentially this is a relatively crude case of cabin temperature control by regulating the volume of heated air or cooled air coming from the heater and evaporator unit respectively.

Control cabling attached to the temperature control slider shuts off the flow of cold air circulating around the evaporator unit from getting into the vent system of the cabin.

A picture showing the internal cabling from behind the fascia. Picture Courtesy (Hyundai Santro Service Manual)


When you turn the A/C switch on and slide the temperature control slider all the way to the red, the compressor is working full time, but none of the cold air is actually getting to the cabin.

With the AC switch on, and the temperature control all the way to the blue, the compressor is still working full time, but what happens is that all the air inside the cabin is coming from the evaporator unit - and it is just cold air. None of the hot air is coming as that flap is closed.

Unlike more sophisticated cars, there are no sensors to detect cabin temperature in this car or even vent temperature, and therefore switching off the compressor is left to the thermistor circuit shown -i.e. if at all thermistor gets to the non-operating temperature range. (picture courtesy Hyundai Santro Service Manual)

[Leop]

Hi

I have a Ford Figo which has been regularly serviced by Metro Ford Bangalore (St Marks).
During my last service (50K), they diagnosed that my ac hose is leaking and that it would need to be replaced. I agreed and got the work done. The hose in question is listed as the 'Condenser to Evaporator Line' in the manual and as 'Hose Suction AS6919835AC' in the bill.

Attachment 1255892

They have diagnosed the ac leak initially by the hissing noise being made by the evaporator when the ac is turned on and that the cooling power of the ac is weak. They then found a very small leak in the hose and thus recommended replacement. There is no visible damage on the replaced part they claim the leak is at the valve, I have no reason to doubt them about the leak.

My issues are:
1) They have billed me for 250 ml of 'Compressor Oil'. I unfortunately did not notice this till I reached home. Considering only a line was changed, 250 ml seems ridiculous. The manual references something like 10 ml over the recovered amount.
I suspect my compressor will get damaged with that much additional oil. How would I diagnose if the oil is over filled (without opening the whole thing up)?
I have considered that they may have billed me for an entire container, but considering an opened container of refrigerant oil has a long shelf life it seems ridiculous to not return the unused amount to me or use the same container for multiple customers.

Attachment 1255891

2) I have been complaining of hissing and a weak ac for the last two services (30K & 40K). The service adviser has always then revved the engine to clear the noise and show that the ac is cooling. I then left the complaint at that since they were making a fuss. I should have insisted that they write the complaint down. I had even contemplated taking the car to an ac guy to get the gas topped up (Note: We had another hose changed earlier due the car grounding at ~8k Km, always suspected that they had under filled the gas at that point, never suspected another leak).
My issue is that this is my first service out of warranty and the issue clearly existed before the end of warranty. The hose should be covered by warranty. I am not saying they did this on purpose but incompetence and fraud have the same effect on my wallet .

Things Ford can take away from this:
1) Customer typically have a longer relationship with you than your service advisers.

2) Record everything. Computers make this easy. Record everything the customer said at the time of handing over the car, even if the customer is later convinced that it is not an issue. Including the most trivial, crazy complaints (like my rear leg room seems to have reduced (actually possible in a Figo with their crappy rear seat hinge)).

3) Record all activities in the workshop if you filled 10 ml of a 50 ml container record the 10 ml.

4) I have been reasonably happy with Metro Ford and this is my first major issue with them. Their cleaning is superb, advisers polite and reasonably on time. I just hope they don't cost me a compressor.

The big question is how do I diagnose an AC system with too much oil? How much oil is too much and is a hydraulic lock/other damage a real possibility?

[SirAlec]

if there is a leak, there will be no cooling at all. eventually the gas will leak out. Period!

About the oil. I dunno about the bill. But if a ac recharge machine is used, it will fill the oil automatically. And the oil comes billed as part of refill and not separately.

[joybhowmik]

Originally Posted by SirAlec

if there is a leak, there will be no cooling at all. eventually the gas will leak out. Period!

correct

About the oil. I dunno about the bill. But if a ac recharge machine is used, it will fill the oil automatically. And the oil comes billed as part of refill and not separately.

yes. the recharge machine filters the oil out of the refrigerant. See post above showing the recharge machine ,and the oil bottle in white plastic. And yes , it's part of the cost of recharge.

[vnabhi]

Nice article that got me thinking, but divergent views have got me confused!

While on this, my WagonR will complete 13 years this month end, and is still running on the original AC gas. The AC has never been overhauled this far, but only the fan belt was changed 2 or 3 years back. The AC cools decently, but not as good as the Fords that I bought later.

Is there something I need to overhaul or replace? My annual service was done only a month ago.

[SirAlec]

Originally Posted by vnabhi

Nice article that got me thinking, but divergent views have got me confused!

While on this, my WagonR will complete 13 years this month end, and is still running on the original AC gas. The AC has never been overhauled this far, but only the fan belt was changed 2 or 3 years back. The AC cools decently, but not as good as the Fords that I bought later.

Is there something I need to overhaul or replace? My annual service was done only a month ago.

I presume you did not service your AC for past 13 years.

Full AC service is needed which include the following.
1. Gas recharge (about 1000 depends upon the place)
2. Cooling Coil service. The guy will open your dash and open the coil housing. Smart one will not even open it (hence no gas recharge necessary on most cases) Just a spray of high jet water in a particular way will clean the coil. Mat need to be removed. But its not an issue
3. condenser fins cleaning. This you can even do at home if you have a cleaning jet. or high pressure motor/boring (usual pani wala)

PS: There will be charcoal bottle, most of this old ones have a small window on top (round glass). just check there should be no bubbles. If it then step one is necessary.

[thoma]

Originally Posted by SirAlec

3. condenser fins cleaning. This you can even do at home if you have a cleaning jet. or high pressure motor/boring (usual pani wala)

Is a high pressure jet of water really recommended on the fins? Even if we run our fingers firm on the fins, doesn't it it tend to get bent?

More than once on receiving new cars, I've found paper debris stuck on the condenser fins. These are flown off from a pressure wash of the temporary registration sticker on the bumper. I've tried to remove this paper debris by hand and have bent many a fins; this is why I ask.