Got my A/C operational, everything works as it should, just not cold enough.

Are you ready for some super Shade-Tree Mechanics? LOL In my quest of getting things working on this old girl that I just recently bought, I found I needed a new FCM. Ordered it, and then I found I needed a new compressor clutch coil. So I got that, and took the compressor snout apart.. Well it turns out the nut had backed out and had beaten the splines of the clutch away. I didn't realize this until I had everything apart to replace the coil. Because the clutch wasn't gonna hold the shaft for me, it had to be sacrificed in order to get the clutch off. Its all good, where missing metal was, it can be replaced! By way of a $90 fluxcore welder! lol



So with a functioning clutch, my A/C system works as it should. However it doesn't get cold enough. Even after dark with a 69f ambient, it would still only produce 60f on re-circulation. So its working, just weak. I am going to check later with gauges to get an idea of things, but should i just have it evacuated and filled to the 750g it calls for? I have no idea how many years the system has been inoperable.. But it doesn't seem to have any leaks.

ps. yes, i know thats some BOOGER welding. The welder handle is broken, it feeds when it wants to and arcs without a button.. also i didn't have a mask, as this was far from planned out lol.

It may be nearly empty of gas but I wouldn't bet on it. My bet is that RCV is stuck almost entirely open and thus it's not really compressing. While you CAN change it in the compressor a good part of the time you're wasting time doing it and would be better off replacing the compressor and TXV, plus flush the system well, considering that you need to evacuate the system and have to replace the dryer any time you intend to open it up, so you're doing a decent bit of work to change that valve and if it doesn't solve it you get to do it twice.

Could be the TXV, or the pressure regulator in the compressor, or charge.
Check operating pressures as well as supper heat and subcooling before replacing anything else.

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Thanks for the replies guys. I will get some gauges on it tonight.

Could you elaborate a little further on "super heat and subcooling" ? Not entirely sure what this means.

If the operating pressures are proper.. are we still suspecting the RCV and/or TXV?

There's a chart that says what the temperature relationship is to the pressure of the gas. When you get the pressure on the gauge, most gauges give the temp on them, you measure the temp of the line and subtract the gauge temp from that to get the super heat and sub cooling. How much more heat is extracted from the air after evaporator, and how much heat is removed after the condenser from the Refrigerant.

I say to do this so you know if it's the TXV or the valve in the compressor. If the valve in the compressor is good you should be able to get away with replacing the TXV and leaving the compressor.

Otherwise 8v-of-fury is absolutely correct.

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Have you inspected the blend door for loss if foam?

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eddieleephd said:

There's a chart that says what the temperature relationship is to the pressure of the gas.

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In relation to the ambient temperature, yes? Apparently at an ambient of 90F, it should be at 105psi on both gauges. It was this pressure. Does that indicate the system is not blocked?

wildchild80 said:

Have you inspected the blend door for loss of foam?

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I have not, but it definitely doesn't feel like any heat is getting through now or before I got the AC running. Is it easy enough to check and fix? I have an mk2 here where i could just fit my hand in the box and put some of the metallic duct tape on the blend door. Its been perfect for about 10 years now.

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So I know, people hate it, but I had some r134a in one of those KwikKool cans or whatever. I have used it in the past on at least 10 different vehicles.. its either worked cause it was a little low.. or didn't work cause that wasn't the issue. As soon as I started adding refrigerant the vents started blowing cold, also I am pretty sure the compressor was running solid before doing so. Now it cycles as it should.

First picture is the system as it sat before doing anything;



And the second picture is after about one small can of refrigerant, while watching both high and low side gauges;



Finally, the vent temperatures at 1500rpm and fan on speed 2 with an ambient of 90f in full sunlight;

Guess it doesn't matter how you're supposed to do it. I should know better than to expect a not AC technician to try to diagnose the system before charging it.

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eddieleephd said:

Guess it doesn't matter how you're supposed to do it. I should know better than to expect a not AC technician to try to diagnose the system before charging it.

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Did this offend you somehow? I used a $5 can of refrigerant as a diagnostic tool, what is so wrong with that? Either it worked or didn't work..

Not everyone can know how to do everything, I wouldn't have made this post if I knew how to diagnose it fully by myself.

Now that I understand its importance, and have watched some material. I will get those values for you tomorrow.

Neither of my AC compressors cycle off if the ac is on. It was my understanding that the purportioning valve regulated the refrigerant.

Neither as in neither of my tdi's

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eddieleephd said:

Guess it doesn't matter how you're supposed to do it. I should know better than to expect a not AC technician to try to diagnose the system before charging it.

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Click to expand...

ASE Certified Master Tech?

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WildChild80 said:

Neither of my AC compressors cycle off if the ac is on. It was my understanding that the purportioning valve regulated the refrigerant.

Neither as in neither of my tdi's

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Perhaps you are right.. I am not sure now if that was a cycle or something else.

So on these systems the compressor will turn 100% of the time that the ac is called for?

8v-of-fury said:

Perhaps you are right.. I am not sure now if that was a cycle or something else.



So on these systems the compressor will turn 100% of the time that the ac is called for?

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Mine do, doesn't mean either one is right... I'm actually wondering myself.

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WildChild80 said:

Mine do, doesn't mean either one is right... I'm actually wondering myself.

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Hmm, I know on like my gfs 06 honda, or my 98 jeep, or 88 chrysler I am sure they all cycle.

But they may not use a TXV in the system that regulates low side pressure? I have no idea.

8v-of-fury said:

Perhaps you are right.. I am not sure now if that was a cycle or something else.



So on these systems the compressor will turn 100% of the time that the ac is called for?

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Pretty much, unless the high or low pressure sensor causes it to kick out.
There's a reason I recommended the action I did.
The pressure temperature relationship works running or not.
You need to diagnose a system properly in order not to throw parts at it, so if you don't do a proper supper heat sub cool check you won't know where to start.

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eddieleephd said:

Pretty much, unless the high or low pressure sensor causes it to kick out.
There's a reason I recommended the action I did.
The pressure temperature relationship works running or not.
You need to diagnose a system properly in order not to throw parts at it, so if you don't do a proper supper heat sub cool check you won't know where to start

Click to expand...

I appreciate your help, I really do. I was just unaware of that test tbh. I am much more knowledgeable on automotive AC systems after today.

Some more knowledge I found out WildChild80.. apparently your stuff is working correctly.

Oilhammer said:

Just an FYI, for anyone reading this:
Many cars use variable displacement compressors, non cycling clutched type compressors of that type have been in the automotive world since back when R12 was in use. However Volkswagen didn't start using them until they switched to R134a, which started in 1993.
But the clutchless non cycling compressors came around later, but some other cars use them too. The basic principle is the same, though. Just that the clutch type never really can get to "zero" displacement like the clutchless type can.
But in either case, it is a more efficient method of removing heat from the car's cabin.

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I believe it started on th A5 platform 2005.5. I remember both my mk4's had cycling clutches(I believe) since I remember seeing the compressor engage the clutch.

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oilhammer said:

No they didn't. As I stated earlier, all R134a Volkswagens that I am aware of sold here use variable displacement non cycling compressors. Just because it has a clutch to engage it, doesn't mean it cycles on and off. If one of those cars DOES disengage the compressor (like, an ALH for instance) while the A/C is in the 'on' position, something is wrong with the system, or the ambient temp is too cold to allow compressor engagement. Otherwise, they will stay engaged and always run, just the compressor's internal mechanism will vary depending on heat load.
Even my 1993 Eurovan has a standard issue non cycling Sanden variable displacement compressor. The very last Volkswagen sold here that was not like that was the 1993 Cabriolet, which was still a holdover A1 platform Golf with an updated A2 era type engine.

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8v-of-fury said:

Some more knowledge I found out WildChild80.. apparently your stuff is working correctly.

Click to expand...

Thank you, I knew it was somewhere around the forum but at this point, too lazy to look for it.

Pay attention to your fans though, I had a fan die on me somewhere in South Carolina or Alabama...the car shuddered and slipped the serpentine belt, after the second time I realized it was my car and not the truck in front of me...felt about like fans going from low to high, long road trip home without AC. I was more worried about locking up the compressor and throwing a belt so I cracked the windows and motored on.

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8v-of-fury said:

Did this offend you somehow? I used a $5 can of refrigerant as a diagnostic tool, what is so wrong with that? Either it worked or didn't work..



Not everyone can know how to do everything, I wouldn't have made this post if I knew how to diagnose it fully by myself.



Now that I understand its importance, and have watched some material. I will get those values for you tomorrow.

Click to expand...

The issue with adding refrigerant is that you overcharge the system and can cause issues with it. The high pressure sensor shuts down the compressor and cycles it because it's overcharged.
The internal compressor valve should regulate the pressure and maintain the proper sub cooling and the TXV should regulate the proper super heat.
So if you have the right subcooling, however, too little superheat; the TXV is bad. On the other hand, if the subcooling isn't maintained, the TXV can't regulate the superheat because the refrigerant is to warm to remove the heat.


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If both low and high side pressures are identical when the compressor is engaged then either (1) the compressor isn't compressing, probably because the RCV in it is stuck wide open or (2) the TXV is blown and wide open, so there's no constraint on flow from the high side to the low side, thus there is no removal of heat (there's no expansion going on.)

#1 is more likely than #2 in my experience but both are possible.

IMHO the correct way is to pull the charge and put the correct weight in. Anything else is just taking shots in the dark on the charge. And yes if the clutch is cycling something is very wrong.


I am wondering if the OP had a very low charge and then after adding some its now cutting out on low suction pressure. But again, you don't know for sure unless you weigh in the charge.

These were my pressures before touching the system. It was only able to cool 10f lower than ambient even after dark.

The pressure doesn't mean that it was properly charged with refrigerant, nor does it mean that it wasn't properly charged.
It means it didn't leave the system completely.
These systems equalize when not in use. And you haven't measured the temperature correct to determine if it was cooling properly. 10* subcooling is actually not far from where it should function properly. Haven't pulled the charge for the vehicle. The subcooling is actually a measurement of the liquid temperature is compared to its pressures equivalent temperature after the condenser. Superheat is how much warmer the vapor is than the pressure equivalent after the evaporator.
As stated before, the Refrigerant needs to be reclaimed and weighed in then the system should be tested to determine the issue.
Otherwise, you're throwing parts at it and it will need a compressor, filter dryer, and a TXV. The refrigerant reclaimed, parts replaced and then vacuumed and recharged.

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Blend door foam gone and/or inoperable.

So, it starting to blow cold as soon as you select the AC, and 32F out of the vents is not correct?

If the pressures aren't too high and dangerous.. Is ice cold air from the vents not the desired action we're looking for? I'm confused on that one. Is there such a thing as a system working TOO good? As it sits, my cabin can be 40f when its 90f in full sun.

I understand the need for the superheat subcool test, but isnt there a dumb luck chance I put the right amount of refrigerant in? lol

A TXV/internally regulated compressor system will work quite well at anything from roughly a half-charge to slightly overcharged, and very well in the 3/4-full charge range.

I would leave it alone at this point, although the missing refrigerant went SOMEWHERE, and the SOMEWHERE is likely still leaking as it was before. So if/when it stops again find the problem the second time

Oh no doubt. Fortunately enough for my backyard ways, there are MANY ways to get something done beside the 100% by the book way lol.

The A4 platform is full of old junk ass cars these days, how much would anyone REALLY spend on it right?