KrashDH

So I picked up a can of refrigerant today (w/ pressure gauge) because I was thinking my system needed a little pick-me-up. I hooked on to the low side and the pressure was hovering around 50-55psi. I know that is a bit high. Who knows how accurate the gauge is though...

So, I went back to the Haynes to read what they suggested you check for low symptoms. One was touching the two pipes going to the compressor. There was definitely a noticeable change in temp between the two, so that checked out.

The second was the viewing test. It said that if while the vehicle was running the refrigerant looked foamy, then you may have low refrigerant...EXCEPT if the ambient temps are very hot (its about 80 today, within what they suggest for ambient outside temp). So this got me thinking there was a possibility it was low, because it had that white, frothy look to it.

But, it also said that "With the proper amount of refrigerant, when the a/c is turned off, the sight glass should show refrigerant that foams, and then clears." This was also my case, which contradicted above.

My a/c seems to run and work fine. It blows cold, but then again I have been in some vehicles that blow COLD. I'm wondering if I can get more out of it. I know it's bad to have low refrigerant and too high of pressures, so I don't want to risk anything. Also, I have owned the truck for 5 years, and I haven't noticed the a/c getting any warmer.

Does anyone have suggestions or is this something that a 2.7 is weak on?

mt_goat

Here's the best writeup on AC troubleshooting I've found:

http://forums.bimmerforums.com/forum...xpansion+valve

KrashDH

Well, I think now that it is related to a fan clutch problem, because I went to check that today, and found out that it spun freely, when it's supposed to have resistance. Anyway, is this a pretty easy replacement? They seem like they are kind of expensive is there a good replacement?

Scratch that...my fan clutch DOES in fact have resistance and there is no play, so back to square 1

FogRunner

First off yes 50PSIG which corresponds to about a saturated suctions temperature of 55degress in the evaporator. So yes that is warm for a normal automotive A/C system (assuming you had the system on recirculate and not fresh air).

ASE and all other standards dictate when taking measurements of automotive system to have it on high fan and recirculate or MAX A/C in American cars.

Now as far as the sight glass being "foamy" or as its properly referred to as "turbulent", there are several reasons for a turbulent sight glass. The most common reason is low charge and the second reason is the ambient air temp is high and there is very low airflow over the condenser coil.

To explain this properly you have to understand a basic refrigeration theory. The system starts with liquid refrigerant being sprayed into the evaporator through a orifice (either a expansion valve or fixed orifice tube).
As the pressure drops the refrigerant absobs heat causing the evaporator to get cold.

To see a perfect example of this is to grab a can of caned air used to dust computers and such. Turn the can upside down and pull the lever and you will see a vapor come out that is extremely cold. Imagine that vapor being sprayed inside the evaporator coil same principal.

After the refrigerant has been flashed or "boiled" into a gas from a compressed liquid in the evaporator its sucked into the compressor where it is compressed and exits as a VERY HOT GAS around 180-210 degrees.

It then goes to the condenser coil where air is used to remove the heat from the hot gas and condense it back to a liquid and is on its way back to the evaporator. Its the same as if you boil water (water absorbs heat and turns to steam) and then you take that steam and cool it off (removing the heat from the steam/water) and it condenses and turns back to a liquid from a gas.

Now back to that sight glass. If the condenser cannot remove all the heat from that hot refrigerant gas not all of it will turn back to a liquid and you will see the remaining gas bubbles of that uncondensed refrigerant gas in the sight glass giving it the turbulent/foamy look. At this point the system is running VERY inefficiently due to the lack of liquid refrigerant entering the metering device (orifice)

A very easy way to tell if this is what is happening is grab the garden hose and spray a good amount of water into the front grill of the truck and watch the sight glass and the gauge pressures. If this sight glass turns clear and the evaporator and high side pressures drop a bit then the turbulence/bubbles were caused by high ambient and there really isn't an issue.

But if the turbulence/bubbles persist after spraying the condenser coil really good with the garden hose and the pressures drop like a rock then you have a low refrigerant condition.

Also if you want to get into a little advanced theory and understand the aspects of the refrigeration cycle more, google "superheat" and "sub-cooling". Superheat deals with the amount of heat the refrigerant vapor picks up AFTER its flashed off at the satuarated suction temp in the evaporator. And Sub-cooling measures the amount for heat removed from the refrigerant in the condenser below the condensing temp/pressure point.

Sub-cooling isn't going to be an issue in automotive A/C systems but superheat is. If you have too much superheat then the cool refrigerant vapor because less dense and will make system loose performance because of the loss of volumetric efficency in the compressor. Also high superheat raises the discharge temp of the compressor which reduces oil life.

This is one of the reasons I almost always run my A/C on recirculate rather than fresh air.

KrashDH

Yes I understand what you are talking about. I graduated in ME and had to take many classes on thermo and heat transfer. So what you are talking about and the terms make sense and are common to me.

Unfortunately, I excelled in welding and CAD and the use of CNC, lathes, and mills...more of the programming/physical side. You make a good point though...I will try the garden hose trick. Most of the tests have checked out, minus the "turbulent" flow while running. I do have cold a/c, but my problem is I want it colder. 50-55 psi is too much. You say that is running warm for a system but to me, I do not want to venture much over this, as the risk increases the chance of damage to the system. It seems from reading it can get very expensive quickly if the wrong steps are taken.

So as far as an automotive standpoint, instead of my heat transfer classes, what do you reccomend? The hose trick and if that checks out dont worry about the refrigerant? And if it fails how much do I add before I start ruining seals and such? The a/c system seems to be very touchy, and this is something I don't want to screw up.

FogRunner

If you spray the coil down and the turbulence/bubbles don't go away then it needs refrigerant and you have two choices.

You can put in more refrigerant SLOWLY and watch the sight glass and pressures.

Or you can do the BEST option which is charge by weight. Basiclly you bleed the system down till just about 5PSI of gauge pressure is left (keeps the air out) and then charge the system per the specified weight on the tag under the hood, the FSM says 22.2 OZ -/+ 1.5OZ)

As someone who as worked in the industry for over 15 years on everything from a small residential A/C to 100 ton commercial chillers and my personal favorite reefer units (carrier transcold).

When ever there is an issue on system charge I evacuate all the refrigerant and recharge it per the manufactures specs. I've lost count how many times I've had to fix a unit that someone had fat fingered with a tank of refrigerant and a set gagues to get it "just right"

Just get you two 16OZ cans of R-134A and dump in both of them and you will be right on spec.

As far as blowing seals and causing system damage you really have to GROSSLY overcharge and get the head pressure to over 275-300psi before your getting in the caution zone.

And as far as venting the 134A out of your system. Its not hurting a thing the vast majority of canned air is 134A http://www.soscleanroom.com/index.as...ROD&ProdID=288

KrashDH

Alright that's some good info...

Yeah isn't that why they switched from R-12 because it was "harming" the ozone layers, and 134a is safe?

Now as for bleeding the system, can I do it right from that low pressure fitting, and when the gauge reads approx 5 psi that's when I need to start dumping it in?

Or is their another way to bleed the system?

FogRunner

They can claim allot of reasons for the phase out of R-12. But the real reason is DuPont was losing their patent and R-12 was going to be mass produced in Mexico (which is still is today). So they came out with a new refrigerant R-134A and guess who holds the patent DuPont of course .

R-12 is by far a supior refrigerant to R-134A but was phased out for politcal reasons much like the phase out going on with R-22 which most people are not aware of until they go to get their house A/C system serviced.

But back to the main question, just hook the gauge up to the low side and slowly bleed it till it gets down around 3-5PSI (main issue is just keeping a little bit of pressure to keep the air out). Once that is done just hook the can up to the low side and start charging.

Be sure to keep the can UPRIGHT so that only vapor comes out. If the can is sideways or inverted it will flow liquid to the compressor and put it in a hurt locker PDQ.

Also be sure to make sure the entire can goes it, it may take a while because as the refrigerant boils out it will cool the can and drop the pressure in the can. Easiest way to check is briefly close the gauges and shake the can, and see if there is still any liquid in it.

Also revving the engine up to around 1500 RPM helps draw it in faster too, just be sure to spray the coil with water every 5-7 minutes to keep the head pressure down.

As as per before keep the A/C set to recirculate and the fan on high.

mt_goat

Aren't there some brands that you need to hold the can upside down?

Thanks for the great info

KrashDH

I'm just curious on the can instructions as well as the manual, it says that you should rotate the can while it's being let in from vertical, to horizontal, back to vertical, over to the opposite horizontal.

So this would be bad to do even though both instructions say this? Do they tell you this because it will clear the can faster, neglecting to tell you that it's bad to let liquid in? I'm confused on this one, but it seems you know what you're talking about...

Oh and is legit to use one of the can gauges to evacuate the refrigerant down to 5 psi? I guess I mean I can push the needle down and then periodically check the pressure with the can gauge, and as it gets closer check it more often? Or are they not an accurate source for pressure...? I have read they are pretty close for low pressures but as the pressure increases the tolerances for readings are all over the place...

FogRunner

There are some small cans that are an oil charge with a OZ or two of R-134A to push the oil charge. Oil charges are to be charged upside down otherwise the oil will stay in the bottom of the can. The only other liquid that can be safely injected into a suction side is UV dye pack with a special tool which allows your to do it SLOWLY.

The cans of R-134A with UV dye are a PITA and should be used as a last resort when trying to find a leak.

Back to can position, the main reason for keeping a can upright is because allowing liquid refrigerant into a compressor is the EXACT same thing as sucking water into the intake of your engine and hydro locking it. You can't compress a liquid and A/C compressors are no exception (I've seen this first hand with techs trying to save time).

The only exception is on cars with an accumulator can. This "can" allows liquid refrigerant that didn't boil off in the evaporator to boil off inside of it so as not to reach the compressor. When a car is equipped with a accumulator they normally put the low side/suction side service valve on it.

Because of this you can dump liquid refrigerant directly into the accumlator and it will boil off before it gets to the compresser.

Not trying to sound like an infomercial (my wife tells me I do sometimes LOL) but I bet your saying to yourself, Hey my Toyota doesn't have one of those wonderful accumulator devices,,, where can I get one ??.

Well it may sound like a blessing but its actually the opposite really. The reason vehicles are equipped with an accumulator is because the manufactures wanted to go the cheap route and put in an orifice tube which is just a restriction or disc with a VERY small hole it in for the refrigerant to spary through into the evaperator.

The problem with this system is there is no way of regulating the amount of refrigerant sprayed into the evaporator depending on load (hot,cold, high/low fan, fresh or recirculate). So under low load conditions there is liquid that isn't boiled off and something has to be done with it hence the accumulator.

Now Toyota has taken a different (and better IMHO) approach and used a device called a thermostatic expansion valve which opens and closes a variable orifice depending upon load in the evaporator. This maximizes the efficiency of the system and negates the need for an accumulator.

The only time a fixed orifice should be used is in a fixed load system. The only places you see them today is household refrigerators, window A/C units and for some reason in American cars. Everything else you will find a TXV in and for good reason.

I think the main reason that the American car makes keep using the accumlator/fixed orifiace is because its very tollerant of refrigerant charge variances (allows for bone head techs who don't know what they are doing).

And as far and evacuating the system you can just use a nail pushing the vale core and letting it blow till it gets to where you just feel a gentle flow and then you can go ahead and weigh in a new charge. (Just don't get frost bite from the refrigerant IT HURTS, I had a fitting blow off years ago and got BAD frostbite on that majority of my hand)

KrashDH

Frostbite that's crazy...but yeah I guess if precautions aren't taken it can get the best of you. Well the can I have says it has a mixture of oil and sealants for the system... to lubricate and if there is a potential leak...

Is this the reason they say turn it, because oil is included? I guess it's not 100% R134a because of this...

So you opinion? It has the lubricants for the system in the canister? Still hold it upright or work it back and forth? I'm not going the dye route, because I don't think there are any leaks.

atistang

where is the sight glass at, my tacomas ac is alright but not great, if it is over 85 degrees them i have to run the fan on high and recirculate the whole time to maintain a comfortable temperature

FogRunner

If it says it has any type of "seal restorer or leak stopper" then DON'T USE IT.
There are only three things you should ever put in a A/C system and thats refrigerant,oil, and a oil/UV DYE mix when necessary.

Those leak stoppers are snake oil and cause ALLOT more harm than good over the long term.

The only reason to put an oil charge in a system is if its a chronic leaker and your having to put refrigerant in every couple of weeks or once a month. The reason for this is because oil is carried with the refrigerant and where ever there is a refrigerant leak, oil will leak out also.

But as far as a system that hasn't needed any refrigerant in years and you doing a simple evac and recharge, use cans of pure %100 R-134A and nothing else.

KrashDH

The latter explains my situation... I would do an evac and then refill...here's my other question, your first statement says that there is oil that is carried with the refrigerant. So, if i were to let it out at the low valve, wouldn't it be letting oil out as well, which would mean I would need refrigerant AND oil? You are saying to use pure 134a, but if my oil comes out with the refrigerant, then what? Does the "pure" refrigerant contain oil?

KrashDH

Not sure what year you have but mine is over by the drivers side headlight assembly. Pop the hood and look around there, you will see it.

FogRunner

A can of R-134a contains nothing but refrigerant and NO OIL. Of the total oil charge of a system the vast majority of oil 70% stays in the compressor while the rest 30% lingers in different parts of the system (evap,condenser,receiver ETC) as it carried by the refrigerant.

If you were to vent the liquid (high pressure side) then yes oil is gonna blow all over there place and you get into that issue. But venting low velocity low pressure from the suction side line will not cause you to loose any oil. You may feel a little slickness on your hand or glove from a couple of drops of oil that mist out.

So no if your just doing a evacuation and recharge, adding oil isn't an issue.

KrashDH

Ok that's good to know. Because ya the system has never needed to be refilled, I just figured after 10 yrs it's time for a refrigerant swap and that might do the trick!

FogRunner I appreciate ALL of your info on this subject. It definitely informed me about a/c systems and knowing a bit of info about it makes me not so hesitant to work on it. You brought a lot of good information to the table and I hope others will find this thread as informative as I do.

mt_goat

X2

aviator

Great info here fog... my system is giving me headaches too it needs a recharge... are you familiar with the Duracool line of DIY enviro friendly coolant products? are they any good? They are the only type you can get around here...