Any benefit in insulating the Low side AC line?

[mechanicx]

Originally Posted By: gathermewool
Originally Posted By: duaneb9729
one point that needs to be considered is how the a/c works in the defrost mode, it may very well need the heat in the engine compartment to vaporize the ref. to protect the compressor in the winter.


Good point, but wouldn't the hot air be great at vaporizing the refrigerant?


Normally the evaporator is ahead of the heater core. Outside air normally always goes over the evaporator, whether the A/C is turned on or not, and then depending on the temperature selected it gets diverted across the heater core.

Now if the vehicle has an heater valve I assume the airflow still works the same way, just that as you turn the heat up the heater valve is opened. It might depend on the model though.

 

[Chris142]

A few years ago Ford decided to cover their metal accumulators with a foam like covering. All the foam did was allow moisture to rust holes in the accumulator which caused a leak.

Putting anything on your low side line may cause the same problem.

 

[mechanicx]

Yeah I don't think insulating the low-side is a good idea or will help much. Most GM accumulators aren't insulated either, just a big can of aluminum often times close to the engine in the engine compartment. They must have fond insulating the lowside unnecessary.

 

[JTK]

Originally Posted By: gathermewool
...The purpose of the compressor is to impart work on the system in the form of compression..


The "work" is done across the expansion valve. Like said, the compressor's only purpose is to raise the pressure to keep the cycle going.

Joel

 

[onion]

Originally Posted By: Chris142
A few years ago Ford decided to cover their metal accumulators with a foam like covering. All the foam did was allow moisture to rust holes in the accumulator which caused a leak.

Putting anything on your low side line may cause the same problem.


Agreed.

I think gathermewool's argument is completely wrong... based on a fuzzy understanding of the system. Like Gary Allen said- adding heat to the low pressure side can ONLY increase the amount of heat that the compressor has to 'move'. And it can ONLY increase low side (evaporator) temperature. From both a mechanical efficiency standpoint (work in) and a cooling standpoint (low side temperature and total system heat load), insulating the low pressure side can only be an improvement. It will definitely reduce heat load to SOME extent (the question, though, is how much.. it might be negligible for all I know).

'Slugging' is not an issue with a properly charged ac system- this is something that happens when charging a system incorrectly. Another problem caused by liquid-charging the low side of a running ac system (even if it isn't to the point of 'slugging' the compressor) is that the NEW (read oil-free) refrigerant can temporarily wash the oil out of the compressor cylinders, causing damage due to lack of lube. Of course, this is a non-issue in a closed and properly charged system (as the refrigerant will be carrying oil).

So from performance, efficiency, and reliability standpoints, I see nothing wrong with the insulation idea.

The big HOWEVER is that, like Chris said, several manufacturers have done this over the years. I don't know about automotive applications, but this has been done routinely on heavy equipment. And it causes corrosion. The insulation traps moisture that condenses around the cold line. Steel a/c lines on certain John Deere tractors routinely rust through because of this. And even aluminum lines will corrode- particularly at the fittings.

So personally, I think you might see a degree or two of benefit. But I don't know if it'd be worth the trouble. If you do break out the insulation, then keep it away from any fittings... else you'll be sorry down the road.

 

[labman]

Oooooooooooh, my head hurts. The vapor coming out of the evaporator is still cool. Just how cool depends how much and warm of air is being blown through the evaporator. The more heat it has absorbed, the more work to remove the heat from the system. The heat is the sum of the heat absorbed from the cabin air and any other heat it picks up before reaching the compressor. So logic tells me insulating the vapor line should reduce the heat it picks up and the heat the system has to work to reject. Another bit of info is that my home A/C vapor line is insulated. After all, I had to replace the foam after the one Lab ate it.

One flaw I see in my logic is that if it really does any good, why doesn't the EPA require it, or more manufactures do it in pursuit of the almighty CAFE? Initial expense and maintainence problems never seems to have bothered the EPA.

I am tempted to do so. Thanks to the EPA, the auto companies have downsized the A/C to where it barely does the job.

 

[rcy]

Originally Posted By: labman
Another bit of info is that my home A/C vapor line is insulated. After all, I had to replace the foam after the one Lab ate it.



Without actually seeing your home A/c system (I can see my own though) I bet the last few feet or so of the low side line on your home A/C is not insulated. Why don't they insulate the line all the way to the compressor?

 

[labman]

What the dog ate was between the foundation and the compressor. Back at the evaporator, they wrapped a foam tape over the bend leaving it.

 

[duaneb9729]

when we install central air conditioners, we insulate all the way to the access ports on the unit.

Most guys don't, we like the look, and it feels wrong to leave a foot of uncovered suction line.

 

[Chris142]

Your cars AC compressor is cycled on and off with a low side pressure switch. On @ 40psi and off @ 20 psi or there abouts.

Insulating the line from heat could make the AC compressor clutch cycle on and off more which would cause more wear.

The system will not cool below the 20 psi setting in the switch so insulating the line won't do anything as far as temp out of the vents is concerned.

It will cause corrosion to the metal and aluminum lines.

 

[gathermewool]

Oh, this is getting good.

I'll be back later tonight!

 

[si1491]

Wow, this is good stuff, thanks!
Ok, for clarification, what think I am trying to eliminate is extra heat that the system has to get rid of (via the compressor and the condenser (mounted in front of the radiator), such as mentioned by Gary Allen and onion). The system is already trying to get rid of the heat from the cabin, why add extra heat from the engine compartment? When asking a co-worker, who has experience with ACs, what could go wrong if I insulated that line, he mentioned about the hydro-lock that might happen if the compressor receives liquid vice gas, also previously mentioned.
On the EVO 9, the under hood temps can get quite hot compared to the Toyota. The EVO's AC compressor suction line , connects to the compressor and runs partially between the radiator and the exhaust manifold. This line (the entire length, from the firewall to the compressor) is scorching hot when the AC is not on, as for actual temps, I will have see if I can take some measurements (measure the surface temp of the line as it enters the engine bay from the cabin and as it enters the compressor). I will also see if I can dig into the repair manual to see exactly how it works and how it interfaces with the heater because, as I have noticed, the AC will be on when the defrost position is selected on the HVAC dial (I assume it is to de-humidify the air). I also noticed that the compressor is off for about 8 seconds, and on for about 15 seconds, 85degF outside temp, car was stopped at a stop light, the condenser fan was on(always on when the AC is turned on).
As for insulation, I am considering using insulation tape, such as DEI Cool Tape, http://www.designengineering.com/products.asp?m=sp&pid=30, but if anybody has successfully used something else to do this, what did you use?

 

[labman]

Part of the reason to run the A/C in defrost mode is to keep the system from setting unused for 6 months. Worst thing thing there is for machinery.

As part of sorting out the misinformation here, I read through my shop manual, and there is a switch and a relief valve to protect the compressor from liquid Freon, hydrolock.

The system is designed to vaporize all the Freon in the evaporator. No matter how well you insulate it, as long as the air under the hood is warmer, it is going to pick up heat, just less of it if insulated. If the air is colder, the less heat it will lose if insulated. I don't see insulating it leading to the vapor condensing.

I have been thinking of the foam stuff sold for water lines. I doubt it will take the heat near the exhaust. Maybe that is part of the reason insulation isn't OEM. Maybe need to look at the fiberglass stuff meant for steam lines. I do think you want a tight fit to avoid moisture under it.

 

[mechanicx]

Originally Posted By: Chris142
Your cars AC compressor is cycled on and off with a low side pressure switch. On @ 40psi and off @ 20 psi or there abouts.

Insulating the line from heat could make the AC compressor clutch cycle on and off more which would cause more wear.

The system will not cool below the 20 psi setting in the switch so insulating the line won't do anything as far as temp out of the vents is concerned.

It will cause corrosion to the metal and aluminum lines.


Exactly. Although if you have a GM Variable displacement system the compressor won't have to cycle more. The only time insulating the lowside may help is when the weather's very hot and the A/C system is maxed out and running almost continuously, then insulating may lower your lowside=create lower evaporator temps. Sure, insulating the low side might make the system slightly more efficient or drop the temp a degree or two when it's maxed out, but the difference would be very slight and not worth the corrosion issue.

Also insulating the compressor is not going to increase the risk of liquid hitting the compressor. It's the job of the expansion valve or the accumulator in orific tube systems to prevent that.

 

[rcy]

Originally Posted By: si1491
The EVO's AC compressor suction line , connects to the compressor and runs partially between the radiator and the exhaust manifold. This line (the entire length, from the firewall to the compressor) is scorching hot when the AC is not on, as for actual temps, I will have see if I can take some measurements (measure the surface temp of the line as it enters the engine bay from the cabin and as it enters the compressor).


Are you sure that's not your high side line? Normally, the high side (liquid) line is thinner than the low side (suction) line and is very hot. The low side tends to be thicker and is cold. People often get them reversed, thinking the hot line must be coming from the evaporator and is hot because heat from the cabin has transferred to it. In fact, the opposite is true. The high side line is hot liquid that is metered or 'sprayed' into the evaporator. As it turns from liquid to gas in the evaporator, it gets cold and as cabin air flows over the evaporator cabin heat is transferred to the cold gas.

I'm no expert and I'm sure there's more involved, but as I understand it, that's the system in a nutshell. Compressor compresses cold refrigerant gas, it get's hot as it turns into a liquid, goes through the condensor (in front of the radiator) which lowers the temp somewhat (not quite sure of the role of the condensor actually), then to a metering device before the evaporator as a hot liquid which is then metered into the evaporator turning cold as it changes from liquid to gas and picking up heat from the cabin, then back to the compressor to do the whole dance againn.

 

[punisher]

Originally Posted By: rcy


I'm no expert and I'm sure there's more involved, but as I understand it, that's the system in a nutshell. Compressor compresses cold refrigerant gas, it get's hot as it turns into a liquid, goes through the condensor (in front of the radiator) which lowers the temp somewhat (not quite sure of the role of the condensor actually), then to a metering device before the evaporator as a hot liquid which is then metered into the evaporator turning cold as it changes from liquid to gas and picking up heat from the cabin, then back to the compressor to do the whole dance againn.


Well, the compressor outlet is a a high temp gas. It doesn't become a liquid until it goes through the condenser core (gas in at top, liquid out at the bottom of the core). At the orifice/expansion valve the high pressure liquid becomes essentially a "mist" of refrigerant droplets that travel along the evap core interior and evaporate, pulling heat from the evap core.

 

[mechtech2]

I talked to a mechanical engineer for a very large fast food chain, who's specialty there is in designing heating and air conditioning for the stores.
He said insulating the line is better.

 

[Vizzy]

I definitely take the side of those that say NOT to insulate that low side line...

Sure you might get a small decrease in output temp..BUT is 1 degree or so worth the cost of replacing the corroded lines earlier than the mfr anticipated with factory set up? Not for me. The engineers probably know a thing or two about this concequence.

 

[swalve]

Originally Posted By: mechtech2
I talked to a mechanical engineer for a very large fast food chain, who's specialty there is in designing heating and air conditioning for the stores.
He said insulating the line is better.


Correct. The air conditioning system's job is to move heat from the inside of the car to the outside of the car. The more heat that is added to the system that doesn't come from inside the car, the less efficiently it will run.

What the original guy was talking about is partially correct. He was just applying it wrong. The greater the temperature differential, the faster the heat will move. But you have to also take into account the temperature differential across the evaporator. You want it to stay cold enough so it will pick up heat efficiently the whole way along, not just part of the way. If the liquid line is at ambient, there is less heat in it, and it can absorb more inside the car. If it is above ambient (because the condenser couldn't shed all the heat off), it will have less capacity to pick up heat.

You also have to take into account when conditions are less than optimal, like reduced airflow. The system is working its tail off just to keep up, and you don't need it doing extra work.

Maybe it doesn't end up meaning too much, since he is also correct that the phase change does a lot of the work, it does make a difference at the margins. If the AC unit doesn't have to move extra heat, it uses less energy.