Oh, OK thanks, so the idea behind should be like this, as you indicated in your earlier post the refrigerant is shared between front/back compressor, so for better refrigerant cooling they might have kept it controlled from the front switch itself, is this be the possibility?

Thanks for the clarification, so the A/C compressor gets de-activated once the specified temp is reached, that seems to be good. I was more worried on this part, and in my short span of ownership I never tried these things as well. thanks for the info

ALso check your vehicle temp needle next time this happens.

Even if the cooling coil is dirty, some cooling will be there.

I assume installation was done by an expert mechanic, But make sure he tuned the thermostat and expansion valve to the setting just so.

there is no such thing as two AC unit, except for buses and trains.

AC unit is single but with dual cooling coil in a closed loop. It has control for fans only.

AC condenser switch off- i assume you meant AC compressor. Condenser is nothing but a kind of radiator. It even looks the same and sticks in front of radiator.

All AC Compressor gets switch off, even home ones, (except newer inverter ones) after a predetermined temp is reached.

This is a really useful thread! Thank you everybody

The rear evaporator sound is audible when sitting in the third row. Thanks for clarifying what exactly it is-- for a long time I used to wonder whether it was just a "blower" or whether there was actually another "compressor" there (since I had read something to that effect elsewhere on this forum). The ceiling on/off/speed switch for the [fans blowing over the] rear evaporator is only marked "rear cooler" which doesn't really throw too much light on the issue.

I remember our Qualis used to have one dashboard button marked 'A/C' and another right next to it marked 'Full', which presumably increased the cooling at the expense of fuel efficiency. We rarely used 'Full' as the cooling was usually good enough without it. Any idea how that worked?

I have an '09 model Innova without climate control. There is a rotary knob with blue markings on the left and red on the right. I knew that the red settings would only provide hot air from the engine area, but I assumed that within the blue markings there was some degree of thermostat control. Interesting that there isn't. So I guess it won't improve efficiency to move that knob towards warmer in winter or in rainy conditions-- the compressor will keep working at a predetermined level regardless of that knob's setting. Is my understanding correct?

A couple of other questions:

(1) I had some issues with window a/c's at home recently and was ticked off by the repairman for not having 'serviced' them more frequently. I have no problems at all with the cooling in my Innova. Is any particular preventive maintenance servicing of the a/c system required if there are no symptoms? Or will it be covered under the general periodic servicing at the ASS?

The owner's manual stipulates inspection of the "cooling and heater system" at 40k km, 80k km, and every 20k km after that (inspection and cleaning of radiator and conderser, and inspection of hoses). It also stipulates checking the refrigerant level every 20k km. But I'm not sure whether service centres follow these guidelines exactly. As far as I know the refrigerant has never been topped up in the 90k km that the car has run so far. It is due for the 90,000 km service next week but I am taking it to a tyre and a/c shop this Saturday (day after) so could have it checked out there-- but since the cooling is working fine, the last thing I want is for them to needlessly drain and replace the refrigerant (and charge me for it) just because I mention the words "AC" and "service".

(2) Is it normal for water to drip onto the driver's legs from behind the dashboard (presumably from the evaporator)? It does not happen often but I would imagine there is a system which should prevent it from ever happening, in a semi-premium vehicle.

(3) Of late I have been getting more than the usual amount of smells from outside the vehicle, even though the slider is set to cabin recirculation. I'm guessing this is a mechanical system and due to age the flap is no longer fully covering the external air inlet. Can this be rectified without affecting the rest of the system (and replacing the gas)?

Here is another guy with the same issue in the same car (of same vintage):

Any thoughts, Ray (since you so kindly offered!)?

You are welcome!

The rear evaporator is performing the function of a "cooler". The refrigerant turns into a gas in the evaporator, thus abstracting heat from its surroundings. But I am sure one can forgive the Japanese for their interpretation of the English language.



No idea. Having said that, I don't think the compressor would work extra hard if one pressed the button (if that's what you mean by cooling at the expense of fuel efficiency). It could be something to do with the blower but only a discussion with someone familiar with Qualis can shed some light.




No. In the Innova, the red settings would source the airflow from the heater (just aheat exchanger) under the dashboard which by the way operates by allowing cabin air to be heated up by hot water hose entering it (heated by circulating around the engine) .

Moving the control just moves the flap which controls the blend of hot air coming out the vents. Moving the control by itself to the blue zone, won't provide any cooling, unless the compressor is switched on. And the compressor switches on , only when you press the A/C switch.
Having said that, once the A/C is switched on, there is a thermostat in the electrical line, which would turn the compressor off -from time to time once max. cooling is reached. But you won't notice that as the threshold is not normally reached in Indian conditions.


a) Don't allow dust/mud to accumulate on the floor. Keep your mats clean & dry. This is because, the cabin air is cooled by sucking in the air from the footwell area. And if there's dust or moisture , it can get sucked in as well - choking up the cabin air filters (2 of those -front and rear), or worse - the moisture can even cause rust in the evaporator.
b) Once in a while hose down the engine bay with clean water spray. Pay particular attention to the spray reaching the radiator and the condenser (behind it).
c) Once in 2 - 3 years get the cabin air filters changed. Note this will mean getting the evaporators out, which also means that the entire system needs to be evacuated of refrigerant,and then refilled to manufacturer recommended psi.
d) Over time, rubber perishes. So every once in a while say around 5k kms check the hoses, particularly at the joints, for any cracks. It's at the joint that the hose is usually maximally stressed- so that area wears out quicker. If you notice cracks - just replace it.

No.

The manual is correct in requiring an inspection. Note the inspection would be 'invasive' - in that refrigerant needs to be evacuated , before cleaning of radiator and condenser. So there's an element of disconnecting incoming/outgoing lines into both of these.

No the service centers don't follow them. You need to remind them. And then they will do it.

It's been 90k km, but no drop in cooling efficiency. I suggest you to just get the cabin filters replaced. Note, this would require evacuation of refrigerant and refilling.

No it's not normal. This would likely be a crack in the evaporator housing (made of plastic). Get it replaced if it's too much of an issue.

Yes. It is a mechanical system. The wires between the slider and the flaps need to be checked. If those are found to be okay, then the flaps themselves need to be checked if these are in the correct positions.

May feel a stupid question, but all these years of 'IT' has transformed me into a noob.

This got me wondering about, from where exactly all the cold comes from?

Or in other words, when does the refrigerant show a maximum reduction in temperature?

A) Is it at the condenser?
{ }

OR

B) At the expansion valve, due to reduction in pressure?

It would be nice to mention the same in the above quoted paragraph of the opening post.

During condensation, there's no significant drop in temperature of the refrigerant per se. There's only transfer of heat to the outside air. As can be seen from the pressure-enthalpy curve - the enthalpy (heat energy) reduces while the state changes (from gas to liquid).


In the expansion valve, the compressed liquid (which btw is still at its boiling point) for that high pressure is De-pressurized, reaching the low side pressure point. See chart below. At ambient temperature of 32 degrees celcius , the pressure of refrigerant in the expansion valve reduces from 260 psi to about 50 psi. The temperature of the refrigerant also reduces (subcooling) at this stage.



At this low side pressure, the refrigerant's boiling point is lower. So when it goes into the evaporator, at this low pressure, it starts boiling, taking away the heat energy from the ambient air, thus dropping the temperature in the cabin.

Hope this explains.

Slightly OT, but still related to ACs. In case of manual AC (non-climate control), does cabin cooling temperature selection have absolutely no impact on fuel efficiency? Reading the article on the front page it seems the compressor's clutch will be engaged for the entire duration AC is operational irrespective of what temperature is set. The answer may lie in knowing how the pressure is modulated inside the compressor. Thoughts?

Cabin cooling temperature (usually controlled by a slider control/rotary control in the dash) is achieved by mixing the air flow into the cabin (see post 24 of this thread for a very rudimentary setup).
It has absolutely nothing to do with the high or low side pressures in the AC system.
Compressor clutch is engaged for as long as the AC Switch , Low-ressure Cut-off switch and thermistor are all closed. For all practical purposes this implies the the AC switch as it's rare for the low pressure cutoff switch or the thermistor to open under normal operating conditions.
So a delta fuel efficiency impact due to selecting a very low or very high setting, will be marginally different if at all.

At 70,000 I was advised to go for a comprehensive ac service that would have set me back by Rs. 3000. I almost believed them till my brother-in-law told me that his wagon R has been giving him ac cooling for 7 years and he has never got the ac serviced. I googled and realized that it was most probably the ac filter causing me trouble. I googled for ways to clean it and did a DIY. The AC filter was very very dirty and uncleanable. The website that showed how to remove it also told me that it could be washed with detergent and I used Arial detergent to clean at least 1 kg of black dirt from it. It has to be completely dry before use or it can cause problems. So let it dry for a day in hot sun and when I put it back and switched on the ac the cooling was as good as new. For lazy people, you can go for replacement , costs Rs. 400 + taxes. But if you put a little effort you can prevent the manufacture of one extra piece and contribute to greening the earth. That is the way I approach all replacements, including a mobile phone. I try not to discard something, till it is serving the functionality. Have cleaned the same filter twice and it is still running good. My advice is to clean the filter every month in summers for a great cooling experience. Also clean the radiator with a high pressure jet every 15 days or a month. You will have top see the dirt that seeps out of the radiator to believe that this is an important step that will ensure cooling. Summers are dusty and the dust gets into the ac filter and the radiator to lower the cooling effect.

Thanks a lot Syravi, cleaning AC Cabin filter can indeed bring a drastic changes in the cooling performance, however with time you still need to clean the cooling coils; which are tucked deep behind the dashboard and is generally NOT a DIY job. These coils trap the dust particles which enters directly through the AC vents when you drive in dusty conditions with windows rolled down. I would still advice you to go for cleaning these coils and experience the difference.This job is worth 3K bucks and would take around half a day.

Hi SYRavi,
Did you take any photos of DIY?
Which car are we talking about here??
In case no photos, can you post the steps for undertaking this DIY, with due reference to the car we are talking about.

Usually the filter is located under the left vent, ahead of windshield.

As mentioned by B_W, internal cooling may require some service and at some gas refilling too. This is better left to experts, as one may end up doing something that may leak gas or do more damage than good.

Tks.
Sonu

Be careful while using a high pressure jet for cleaning the radiator. The fins are very soft and you can damage them if the water jet is too strong. A clog or a puncture will bring a lot of harm.

I would say no to using water jets. Maybe using compressed air to clear dead insects, leaves and other debris will be a better idea.

Compressed air will be a safe bet, but in the direction Inside-out (Engine side to Bumper side, same as Air Filter cleaning)

What you said is true. But over a period of time Gas might leak, coils gets clogged. I did the AC overhaul at 1Lakh Service (just as preventive) and could see lot of black muck. The 3k expenses at 1L seems to be ok for me.

BTW I do change the AC/Cabin filters at 10K or 15K intervals. Currently using "Bosch Active Carbon Filters".

Thank you. Will check into it!

My car is Wagon R but the filter cleaning applies to all cars. Yes, you might have to visit a mechanic the first time to understand how it can be done. Later you can do it yourself.

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