Pulsing sound from orifice tube. Causes?

[SMB]

So I'm working on a 2004 VW passat. I installed a pick-n-pull compressor, flushed system, new orifice tube, new orings, pulled a vac for 30 mins, held it for a hour, and put in the correct amount of 132a and pag. The gauges read 30psi and 150psi @ 65 degrees. Seemed OK. The ac blew cold but not nearly as cold as I expected. When I turned the car off you could hear the pressures equalizing through the orifice tube(Hiss). I havnt needed ac in over a month so I thought "welp that didnt really work" and forgot about it.

Today I go about troubleshooting a little further as 85+ degrees is coming. I found out the following:

1. The ac compressor does not cycle off. Stays running the whole time.
2. The system held pressure with no leaks and pressures are still 30 and 150.
3. The orifice tube makes a pulsing sound when the ac is running correlating to a bouncing High Side needle (+-5psi). Kind of like a FFFFFF pause FFFFFF pause
FFFFFF. Maybe sound for 2 seconds, 1 second pause, and then repeat indefinitely.
4. After an hour of the car being off the High Side read 10 psi higher than the Low Side.

Does anyone recognize these symptoms. Perhaps I was sent the incorrect Orifice tube? Some intermittent restriction? Why is the compressor not cycling? Id be happy to provide any additional info to get to the bottom of this.

Any thoughts or suggestions would be greatly appreciated. Thanks

[JohnHere]

First, let's try to determine whether you have the correct OT. Do you recall whether the part with the screen was yellow in color? If so, that would correspond to the OEM OT having the proper .062" orifice. Also, did you install the OT in the right direction?

Your car also has a parallel-flow condenser and desiccant dryer that can't be flushed and reused. Did you replace them both with new components?

Purchasing a compressor from a wrecking yard is "chancy" at best. Whether you get a good one or not is anyone's guess. I believe that your compressor is a variable-displacement type with a manual control valve as well. Professional MVAC shops always replace the compressor assembly—variable displacement or not—with a new one.

[SMB]

Thank you JohnHere, I really appreciate it. So I replaced the dryer but not the condenser. I realize it was a gamble, as well as with the junkyard compressor. I selected a car that has its original ac system intact with no signs of dies or stop leaks. I pulled it and drained it to see if any crap came out of it. Just clean clear pag oil. No other garbage. I think it is functioning as it is supposed to.

My condenser on the other hand, I was less than confident. The OT I pulled out was gummed up with sticky crud. No metal particulates but a pile of gummy crap. making me think the condenser veins might be gummed up as well. The OEM OT was yellow. The one I ordered was a 105- degree fixed OT which was Black and Maroon. Not sure what the size is but definitely not the yellow variable OT that was in there. All websites said the black/maroon was adequate. I live in Washington and it never gets above 105*. Knowing what I know now, I would have went with the variable 105+. I am thrifty and on a budget so a whole new ac system was not in the cards. I.e. a 300 dollar compressor.

Although, I am completely capable of getting the refrigerant reclaimed, installing a new orifice tube and condenser, then recharging. I know condensers are not ridiculously expensive. But on this car, its a bit of a pain in the arse. I'm willing to do it though, now that my first "easy" fix failed and has clear issues.

If you have additional thoughts please let me know, Thanks again!

[SMB]

So I just tested the ac line temp at idle to see if there where any glaring abnormalities. The low side and the high side pre OT where around the same temperature. The line at and after the OT were cold with condensation building up(line going to the evaporator). Not freezing cold but cold. It would appear that the OT is functioning, but why is the evaporator not doing its job?

Also the OT was installed with the colored/screen end facing away from the evaporator.

Thanks!

[JohnHere]

I selected a car that has its original ac system intact with no signs of dies or stop leaks. I pulled it (the compressor) and drained it to see if any crap came out of it. Just clean clear pag oil. No other garbage.

Clean oil draining from the junkyard compressor is a good sign, but we don't know about the control valve. It can fail while the rest of the compressor is perfectly fine.

My condenser on the other hand, I was less than confident. The OT I pulled out was gummed up with sticky crud. No metal particulates but a pile of gummy crap. making me think the condenser veins might be gummed up as well.

A lot of gooey debris on the original OT screen could be from a ruptured desiccant bag, burned oil from the compressor, or a combination of the two. Parallel-flow condensers have micro-tubes running from side to side, and it wouldn't take much of that kind of gunk to clog-up the tiny passageways.

The OEM OT was yellow. The one I ordered was a 105- degree fixed OT which was Black and Maroon. Not sure what the size is but definitely not the yellow variable OT that was in there. All websites said the black/maroon was adequate. I live in Washington and it never gets above 105*. Knowing what I know now, I would have went with the variable 105+. I am thrifty and on a budget so a whole new ac system was not in the cards. I.e. a 300 dollar compressor.

The original yellow OT has a .062" orifice, and I believe the black-and-maroon replacement does as well, so you should be okay there. What makes you think the original OT was the variable type? Probably it wasn't, would be my guess. The system most likely had a fixed OT in it originally. In any event, I think you did good by not installing a variable OT—sometimes called a Variable Orifice Valve, or VOV—because they have been proven not to enhance cooling, and in some instances, have turned out to be downright trouble prone. Your A/C system has been manufacturer designed to run with a particular size of fixed orifice, so I would stick with that.

So I just tested the ac line temp at idle to see if there where any glaring abnormalities. The low side and the high side pre OT where around the same temperature. The line at and after the OT were cold with condensation building up(line going to the evaporator). Not freezing cold but cold. It would appear that the OT is functioning, but why is the evaporator not doing its job?

If the condenser is partially plugged, a combination of liquid and gaseous refrigerant will make its way to the expansion device—in this instance, the OT—so that the evaporator is, in effect, being "cheated" out of the 100-percent liquid refrigerant it needs to function correctly. The evaporator thus provides minimal "evaporation" of the refrigerant and therefore, little to no cooling.

The combination of liquid and gaseous refrigerant at the OT could also be the source of the noise you're hearing.

[SMB]

Hey thanks for following up on all this. Ill try and address to the inquiries in the order that they were presented.

This compressor is a clutch type and when I turn it on and off from the dash controls, it responds appropriately. I know that it is functioning cause the gauge readings go from balanced to 30 low side and 150 high side when switched on.

I'm almost positive the OT was coated in crap from the desiccants, oil, sealants, dies, and who knows what else the previous owner put in there to "fix" it. I'm leaning towards buying a condenser and installing it as a worthwhile step in the right direction.

If the OT and Evaporator were seeing a gas liquid mix, would that show up in the gauge pressure readings? Would that explain why the evaporator inlet (after OT) is cold but the outlet is ambient temp? It seems like the Evap is simply not working or is so dirty there is no air going over the fins. If I could get to it I would shoot it with a thermal gun.

I thought the OEM OT was variable based on a review I read. So, in short I have no basis for thinking it was a variable OT. I do know that yellow OT is rated +105* and the black and maroon one was -105*. The difference I do not know.

I really don't know enough about these systems to go much further aside from throwing parts at it. I don't want to get into a situation where I install parts only to find out the Evaporator is crap. I'm not pulling the dash to install a new core. I would like AC but not that bad. Is there a way to ensure the Evap is in good working order?

I did notice after 5 mins or so of idling and AC on, there was only one drip of condensation on the ground under my car. Does that indicate anything?

PS. I do realize taking it to a shop, might be easier that bugging people on the internet for information. I enjoy figuring things out and learning new skills. So thanks again

[tbirdtbird]

One way or another, you will end up replacing the condenser, dryer, and the OT (again).
Your system is full of contaminants, as is typical of a compressor failure.

And as John mentioned, avoid VOVs

A lot of knowledge about AC repair can be gleaned from reviewing past threads on this forum

And you are not bugging us, those of us that post here are trying to help people such as yourself

[tbirdtbird]

And when you post pressures please post at 1500-1800 RPM with doors open, max fan, max cool, state ambient, and ambient needs to be at least 80F for accurate results

[SMB]

Thank you, the pressures were taken at 65*F, 1500rpm, windows down, max fan, and max cool. I will try again tomorrow, it’s supposed to 87*.

I’m assuming I’ll have to redo the drier and OT because now they are contaminated from not replacing the condenser to begin with?

[JohnHere]

I heard today that Washington and Oregon are supposed to be in the 90's next week—unusual for the mild Pacific Northwest but de rigueur for those of us in typically warmer climates. Regardless, it should be excellent A/C testing weather in your area.

The accumulator, receiver/dryer, or desiccant bag (if integral with the condenser) should be changed anytime the system is opened. It would be interesting to see what the OT screen looks like this time around.

As for the condenser, I agree—definitely replace it, especially if you believe that "unknown substances" were added to the system before you got the car.

The evaporator is another question mark. It's easy to say just replace it as well and be done with it. But often, that job can be a real bear, requiring partial disassembly of the dash as I think you know. Over time, debris like leaves and pine needles can accumulate inside the evaporator plenum. These not only block airflow but can also retain moisture, causing evaporator corrosion and eventual leakage. It's up to you whether you want to take it that far. It'll be a good learning experience, though.

At this point, if it was my vehicle, I would want to begin anew with a dry and completely clean system, meaning no oil or refrigerant, replacing the aforementioned parts, and flushing the rest (again). The compressor should be flushed with the appropriate oil only—no solvents. Any lines with mufflers (can-like objects) can't be flushed and will have to be replaced. If you decide to take a chance and leave the evaporator alone, it can be flushed in situ, but ensure that you thoroughly evaporate-out all the solvent.

The specs that I have for your vehicle are 20 ounces net weight of R-134a and 8.5 fluid ounces of PAG-46. If you have an under-hood decal that says differently, the decal takes precedence.

Feel free to ask any questions that you like. We volunteer our time and expertise to assist in getting people's broken MVAC systems up and running to the best of our collective ability.