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I got my refrigerant re-filled and observed that the pipe going into the compressor gets very cold on the operation of the AC. IF it is getting cold it means that there is a possible heat loss and the compressor has to do extra work in order to extract the heat gained by the refrigerant while passing from the engine area.

My mechanic recommends it otherwise, but it doesn't make sense to me, should I be insulating the pipe to make my air con system more efficient?

  • Yes it has been done and is done for example (Advance Auto Parts) Factory Air Insulation Tape Part No. 59010 – spicetraders Nov 26 '16 at 22:57
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I understand your concern, but you will not find a car coming from the manufacturer which has insulation around the piping. If you think about it, though, it makes sense and here are three reasons why you shouldn't worry about it:

  1. The cold side of the piping is after the evaporator, headed back to the compressor. Any loss here will not make a difference in the overall performance or efficiency of your AC unit. (In the graphic, it's the pipe from the evaporator to the compressor.)

enter image description here

  1. Since the system is designed without the insulation, it may actually be detrimental to some of the working parts for it to be colder (may cause freezing of moving parts/evaporator). Engineers have taken all of this into account when designing the AC unit in the first place.

  2. Remember in order for condensation to form on this pipe it only has to meet two conditions: 1) pipe has to be cooler than the dew point; 2) there has to be humidity in the air. These conditions are very easily met in most situations.

Vehicle AC units are work pretty darn well (even with R134a in them) considering what they have to do and the amount and quickness of cooling they have to do. Why mess with success. If you do, you could be introducing dynamics into the system they weren't designed for and you won't being doing much to improve the efficiency (if you improve it at all).

  • if you had mentioned that the compressor heats the gas then your answer would have been more clearer, I was originally thinking that the compressor is the point where the gas is cooled. – shabby Jun 18 '15 at 5:32
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    @shabby compressing gas (labeled in the diagram) tends to heat it up due to the physics of it, and it seems redundant to say that the compressor compresses, not to mention the colors of blue = cold and red = hot – user2813274 Dec 14 '15 at 2:23
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    Using Armorflex- the pipe insulation used in A/C would not be advisable inside due to the heat generated by the engine. Potential engine fire hazard. – Old_Fossil Nov 27 '16 at 6:53
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Yes ,You should insulate the piping of any air condition not only on your car but its a general rule that the piping from the compressor be insulated.

This will not only prevent heat loss but this will also improve the life of the pipe itself.

Will also prevent uneven coolant leaks in the future, even if it leaks with a proper insulation, the leak will be easy to locate and mend.

  • thanks, why do you think my mechanic was proposing it otherwise? When I asked him why he said its not required, maybe he meant it wont do any good. Was he ignorant of this fact? – shabby Jun 16 '15 at 10:16
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    Not insulating your pipe would not cause any major failure immediately , it will simply extend the life of your pipe and reduce cooling loss. I would not say he was ignorant, its just that insulating is not mandatory but good to have and is cheap – Shobin P Jun 16 '15 at 10:36
  • Anarach, the life of the pipe will not be impacted by insulation unless it is on the verge of melting (which would not happen with aluminum under typical engine bay temps). There are many things that can and will fail before the pipe becomes a concern. – Zaid Jun 16 '15 at 12:52
  • @Zaid Well , I had a similar issue long back and the mechanic at that time said to me its due to bad insulation. Got duped :-( – Shobin P Jun 16 '15 at 12:54
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Regarding "asbestos belt" wrapping. Please do not do this. If you value your health, and if you do not want to get asbestosis tumors (mesothelioma) of the lungs, then do not use any asbestos. I started to use conventional foam rubber on my air conditioning pipes, which is also used for hot water pipes, but I realised that because some of the pipes are close to the exhaust manifold, it could start a fire if they fell onto the pipe. I used some non adhesive 0.3mm aluminium roof flashing to insulate the pipes in places. I also used adhesive rubber backed aluminium that is usually used for roofing repairs. I tried getting adhesive cork but it was not available locally. I drove the car for 10km after completing the insulation (at the time of writing it's early summer in Brisbane, Australia, 28 degrees C, 82 degrees F), and the air conditioning worked very well. I stopped at the shopping center for 30 minutes and when I came out the air conditioning came on cold very quickly when I started the car. Previously it was usually hot at first start due to the non-insulated pipes sitting in the hot engine bay. In general, air conditioning is more efficient if the pipes are insulated. I strongly doubt that I will be "freezing" my compressor. The freezing point of R134A is -103 degrees C. If freezing of the compressor was a problem, then it would not be possible to install air conditioning in cars that are in cold climates for part of the year.

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In order to know if you want to put insulation on the pipeing, you need to understand

a) the working of the AC (as Paluster2 explained) b) need to know which pipe you are talking about

I believe you are talking about the return pipe from the evaporator to the compressor, because this is the pipe usually left uncovered or un-insulated as you mentioned.

Working of AC:

Keep the picture in mind posted by Paluster2, the compressor has to heat the gas anyway, with high pressure.

Lets say the compressor heats the gas to 250 F and your ambient temperature is 100 F so if you dont put an insulation the gas enters at 100 degree and leaves at 250. With insulation it will enter at, lets say 60 to 80 degree and leave at 250 degree.

So as mentioned already engineers have catered for this and it doesnt help insulating your reverse pipe AT ALL!

  • Sorry, that's entirely wrong. The compressor compresses the gas, but does not heat it. The heat energy in the gas is compressed to a smaller volume, resulting in a higher temperature. This is then dissipated in the condenser, where the gas cools down and becomes liquid. If the gas enters cooler, it also leaves the compressor cooler. This does not matter technically, but increases efficiency, because only the heat absorbed inside the cabin has to be dissipated. – sweber Sep 14 '15 at 6:41
  • "The heat energy in the gas is compressed to a smaller volume, resulting in a higher temperature" > means it will have a higher temperature anyway, my point of insulating was to avoid heat flow from engine compartment into the pipe as it enters the compressor. So there is no need of this since it will eventually be pressurized, raising its temperature anyway – shabby Jun 1 '16 at 12:44
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I found my car Ac tube is not insulated and it is moving over the engine. It heated up immediately and affected the efficiency of cooling.I wrapped the pipe by asbestos belt.I amazed to found that the car cooling is even much better than before. Earlier the cooling was not appropriate when I drove the car for 25 minutes.the tube comes out from compressor got heated up so much that I couldn't put my hands over it.after insulating the cooling line pipe I drove the car for 3-4 hours. The results are much better. By doing this I increased my car cooling efficiency by 75 %.about 200 mm of pipe coming out from compressor and 100mm at the end side is still uninsulated. I am trying to cover it up and I am sure it will definitely give me almost 100 %. I am unable to understand why the car manufacturer don't think about it. My car is latest version of Maruti Suzuki zen estilo. Whatever I tried I succeeded. Now I am trying to cover it by glass wool and aluminium foil for better efficiency. I have ordered aluminium foil tape online and kept some glass wool blanket for next .I hope it will definitely change my driving pleasure.

  • @Rahvendra I guess you are mistaken, as I was initially. Have a look at the answer of Junaid. The pipe that is un-insulated is the return pipe. Just by looking at the compressor and if you dont know its working, you cant figure out which pipe is entering and which is leaving. To give you an idea the pipe that is entering the compressor is directly comming from the interior of the car, the pipe that is leaving is going into the condensor. Your efficiency increase might be due to some other factor, or entirely psychological. – shabby Oct 20 '15 at 5:36
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You are absolutely right that the compressor is working harder than it has to. Any time the heat is absorbed, the refrigerant expands and makes the compressor work to compress (and evacuate) the refrigerant. EVERY line in the engine bay should be insulated, including to and from the condenser. You also shouldn't worry about anything freezing over, because, almost invariably, there is a temperature switch on the expansion valve that cuts off the compressor if the line gets colder than 32° F. The only reason this isn't done at the factory is because its cheap to leave them uninsulated (materials and labor).

Efficiency is doing better what is already being done.

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    The refrigerant that enters the compressor is in vapor form . The vapor is converted into liquid when compressed and becomes hot due to the energy involved. Insulating the output of the compressor would cause it to overheat . The refrigerant becomes cold as the pressure is released in evaporator coil after the TX valve. If the air flow is restricted in the plenum it will freeze up. Given the short run of piping using armorflex would be pointless – Old_Fossil Nov 27 '16 at 7:05
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I insulated the return lines of a 2006 mustang years ago, because they are very long and run in the very hot engine compartment. At one point inches away from the exhaust manifold. I can't tell that the air is colder but the compressor does cycle on and off more frequently and the high side pressure did decrease between 15 to 25 psi. That is a lot in the 102F + South Texas heat.

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I insulated the low side (evaporator) lines on both my 1996 Mazda B3000 and 2017 Honda CRV and had a noticeable improvement (decrease in supply air temp.) in both. I used the foam pipe insulation used for insulating home hot water pipes and silver duct tape from where the evap. line exits from the evap. to as close as I could get to the compressor (~3 ft.). Also insulated the drier/receiver in the Mazda with the adhesive aluminum-backed roofing rubber (6 in. wide).

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To insulate pipes to condenser? While your at it why not insulate the condenser. . .the pipes throw off heat as does the condenser, insulating the hot pipes is ludicrous, AFAIK.

The cold pipes, the condensation. Humidity is THE key here. The condensate is from water in vapor form being changed to water in liquid form- a phase change. Water in vapor form holds a large amount of energy, known as latent heat, which is puked into the AC as the vapor becomes liquid water. The problem is humid air hitting those cold lines, not just hot, dry air.

All AC works with latent heat [the refrigeration], swamp coolers work with the latent heat of water. High humidity is the enemy of AC and evaporative coolers.

Experiment- 67 Caprice 327 factory AC, T-Bird electric fan[2 speed]. . .I saw all those water drops on the outlet from the evaporator, then I remembered latent heat. . .Hmmm. . .what if all the heat from water vapor is entering the AC system? So I insulated the metal tube from the evaporator [standard pipe insulation, dirt cheap Lowes or Home Depot.] Outlet temps much improved, coolant temps lowered!

Then I insulated the tube from the POA valve on the way to compressor- now the tube into the compressor is very cold!

Temps all around drop again, vent temp at 32.5 degrees! Coolant temp lowered. Car is at 1000 rpm [est] not being driven Ambient air temp 85 degrees.

It's useful to study up on latent heat and phase changes [gas to liquid, liquid to gas]

Entering the twilight zone- I have a 75 Chevy Monza, factory 350, factory air. Drove a couple of miles to HD to pick up the insulation [yesterday]. Noted coolant temp on arrival home- 200. 85 air temp. So I placed of short section [5"] of insulation on the tube from the combo valve [cold pipe]- a trial fit. Left it on overnight.

So a friend went shopping at the same place I went yesterday- same conditions, humidity, temp [85] and so on. . .coolant temp on arrival at home: 170! Thirty degrees cooler than day before [160 thermostat]! The only change made was adding the short piece of insulation! This truly seems impossible. Did the cooling system suddenly improve [Champion alum with factory flex fan]?? or did the temp gauge suddenly go bad, on this particular day? [SunPro gauge, always reliable] I must assume the gauge is accurate. It seems impossible on two different vehicles.

Advice- insulate cold pipes only. If your pipes show condensation [on the metal] it is humid enough for insulation.

  • Keep in mind that TXV systems don't have an accumulator and most of the new ones feature a TXV that never closes completely when the evaporator is cold (it's meant to keep the compressor cool and lubed up, and to prevent the suction pressure from dropping down too much and too fast while driving, in order to prevent the evaporator from freezing up). By insulating the suction line, more liquid refrigerant is allowed to reach the compressor suction port than with a bare suction line, and you risk slugging the compressor or wearing it down faster. – Al_ Jun 24 at 18:36

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