Noise after AC service

[freakyhead94]

Hello,

My name is Felix from Frankfurt/Germany, new to this forum. Hope you are all doing well. I registered to get some help with the AC system in my car. The car is a 1989 Chevrolet Caprice Classic LS Brougham, 45k miles, stock 305 TBI.

Background info:
-preowner converted the AC in 2021 from R-12 to R-134A since it is absolutely impossible to get R-12 in Germany and they can send you to jail if you still charge a system with it (according to his info, the system was flushed, new accumulator, new oil, new o-rings and the evacuation and refill was done by a professional AC machine)
-AC was cooling nice, however the (probably original) refrigerant high-pressure rubber line from the compressor to the condenser had like a thumb big bubble on the outside, so basically short before bursting
-I managed to get new R-134A refrigerant lines in time without the line bursting and had the shop install it. The accumulator and orifice tube (original fixed GM orifice tube) were replaced at the same time plus every o-ring and gasket that was touched
-original charge of R-12 according to the sticker is 3.5lbs. Since we didn´t know how much the shop of the preowner charged and if and how much the hose leaked, I trusted on the mechanics experience. He drives some GM trucks from the late 80s with basically the same engine and AC system and the system was charged with 3.3lbs R-134A. This was done about 1 year ago in 2023.
-compressor (GM R4), condenser and evaporator are original
-mechanical fan only as original, but I replaced the fan clutch since the old one was always engaged

After the repair, the AC was ice-cold, but at a stoplight or very slow driving, I can hear the refrigerant inside the cab. The noise goes away with faster driving but once the car idles, the noise begins to appear louder and louder, like water rushing through a pipe and disappears when continuing to drive. The hotter it is outside, the louder the noise is at idle. Before the repair, no noises were heard.

If it is very hot outside (around 95°F), the AC feels weak at idle but gets cooler as soon as I drive. On a normal warm spring day like today (77°F), there is no real difference between idle and driving, it gets cold inside the cab to the point where I have to turn the heater on a bit. I thought the noise is coming from the new orifice tube that lets more refrigerant flow. The old one had some black debris on it (not totally clogged, just a bit dirt) but the mechanic said it looks like the original part, so it is kinda normal after 35 years.

Took the car to the shop, mechanic said it can be two things:
-weak compressor that does not generate enough pressure at idle
-not enough cooling at the condenser when its hot, so the refrigerant does not condense completely and gas is rushing through the evaporator

Both ways will be an expensive fix, since I have to order everything from the USA. Price until the part gets here with shipping and tax is basically double the price on Rockauto.

Is this normal behaviour for those kind of ACs or can I trust the mechanics opinion and let him do whatever it needs? New compressor or upgrades for airflow and a modern condenser..

Unfortunately I cannot measure the pressures myself right now, I don´t have gauges yet and most German shops won´t touch american cars, just because they are american and they can´t get any documentation on them, so I have to wait for my shop to have a free appointment (he does 95% US classic cars and the next free appointment is like in 2 or 3 months).

Maybe some of the pros here have heard of that symptom and give me an advice on how to go on.

Thanks and all of you have a nice weekend!

[JohnHere]

My name is Felix from Frankfurt/Germany, new to this forum. Hope you are all doing well. I registered to get some help with the AC system in my car. The car is a 1989 Chevrolet Caprice Classic LS Brougham, 45k miles, stock 305 TBI.

Welcome from the USA.

Background info:
-preowner converted the AC in 2021 from R-12 to R-134A since it is absolutely impossible to get R-12 in Germany and they can send you to jail if you still charge a system with it (according to his info, the system was flushed, new accumulator, new oil, new o-rings and the evacuation and refill was done by a professional AC machine)
-AC was cooling nice, however the (probably original) refrigerant high-pressure rubber line from the compressor to the condenser had like a thumb big bubble on the outside, so basically short before bursting
-I managed to get new R-134A refrigerant lines in time without the line bursting and had the shop install it. The accumulator and orifice tube (original fixed GM orifice tube) were replaced at the same time plus every o-ring and gasket that was touched
-original charge of R-12 according to the sticker is 3.5lbs. Since we didn´t know how much the shop of the preowner charged and if and how much the hose leaked, I trusted on the mechanics experience. He drives some GM trucks from the late 80s with basically the same engine and AC system and the system was charged with 3.3lbs R-134A. This was done about 1 year ago in 2023.
-compressor (GM R4), condenser and evaporator are original
-mechanical fan only as original, but I replaced the fan clutch since the old one was always engaged

Stay out of jail—and stay with R-134a!

Sounds like the conversion was done correctly. Too bad the shop didn't record the amount of refrigerant that the machine recovered because that would've saved you some guesswork about how much to recharge it. The 3.3 pounds net weight recharge DOES sound about right, if not a little low.

After the repair, the AC was ice-cold, but at a stoplight or very slow driving, I can hear the refrigerant inside the cab. The noise goes away with faster driving but once the car idles, the noise begins to appear louder and louder, like water rushing through a pipe and disappears when continuing to drive. The hotter it is outside, the louder the noise is at idle. Before the repair, no noises were heard.

The noise that you notice could be that the system is just a little undercharged.

If it is very hot outside (around 95°F), the AC feels weak at idle but gets cooler as soon as I drive. On a normal warm spring day like today (77°F), there is no real difference between idle and driving, it gets cold inside the cab to the point where I have to turn the heater on a bit. I thought the noise is coming from the new orifice tube that lets more refrigerant flow. The old one had some black debris on it (not totally clogged, just a bit dirt) but the mechanic said it looks like the original part, so it is kinda normal after 35 years.
Took the car to the shop, mechanic said it can be two things:
-weak compressor that does not generate enough pressure at idle
-not enough cooling at the condenser when its hot, so the refrigerant does not condense completely and gas is rushing through the evaporator

A couple of thoughts: The compressor isn't pumping very much at idle speed, but I agree that it could also be a bit "tired" after 35 years.
I also agree that continuous airflow through the condenser is very important, especially with a conversion from R-12 to R-134a. With the car stationary and at idle, and with the old-style OEM serpentine condenser, the condensing function might have been sufficient with R-12. But with R-134a, which is less efficient, cooling can suffer, especially under low-airflow conditions.

Anything you can do to improve condensing will help: Replacing the OEM viscous-drive fan with electric fans (two, if you can fit them); replacing the serpentine condenser with the parallel-flow type; ensuring that all fan shrouds are in place; sealing the gap between the condenser and radiator; and having the system optimally charged all will help cooling performance.

Both ways will be an expensive fix, since I have to order everything from the USA. Price until the part gets here with shipping and tax is basically double the price on Rockauto.

If you can tolerate the way it's cooling now, and from an economics standpoint, leave it alone. If, however, cooling is not sufficient for you, especially at idle, the upgrades discussed here would be in order.

If you DO decide to go ahead with the upgrades, check with Tim at ACKits.com, this Forum's sponsor. He might be able to get you the parts you need at lower prices.

Unfortunately I cannot measure the pressures myself right now, I don´t have gauges yet and most German shops won´t touch american cars, just because they are american and they can´t get any documentation on them, so I have to wait for my shop to have a free appointment (he does 95% US classic cars and the next free appointment is like in 2 or 3 months).

Tim can help you with a good, professional-grade Manifold Gauge Set as well.

It sounds as though you've found an experienced, competent, professional A/C shop—a scarcity in your country. Best to hang onto them.

[Cusser]

I'm thinking to replace the fan clutch to improve air flow at idle and slower-speed driving. Or at least test it well.

[Tim]

John, ACKits.com does not do international shipping. Freight is crazy as is for the US market.

[JohnHere]

Thanks, Tim. Duly noted.

[Tim]

Thanks, Tim. Duly noted.

They should look on Amazon for either Santech, Mastercool, or Robinair. Don't trust the off-brands as the good stuff is not much more.

[freakyhead94]

Hey and thanks for the quick reply! I am not used to forums where there is almost an instant reply, great.

I am surprised that you mentioned the 3.3lbs could possibly be a bit low for the charge. While doing research, I found the GM retrofit guide with that formula: R12 charge x 0.9 - 0.25lbs = R134a charge. In my case, that would be 2.9lbs.
I trusted my mechanic who said that from his experience, these GM systems tend to like a bit more charge and we went with the 3.3lbs. With that noise from the ac, I thought the system is maybe overcharged and whenever I sit at a stoplight for a longer time, I shut the AC off if its hot outside to prevent any damage. Don´t know what can happen if I leave it on with that noise..

If it is hot, the compressor does not cycle off, at least at idle. With slow driving, I can hear it cycle from time to time, so I guess it cannot be undercharged badly. If its cold and I use the Defrost option to clear the windscreen from fogging up, the clutch cycles often. Normal behaviour as I understand.

Right now I can tolerate the cooling as it is, since the car is just my nice-weather-weekend-driver. Gas is about 8$/gal in Germany, premium is more like 10$, so daily driving a V8 here kills your account anyways. But if anything fails like the compressor, I´ll do the complete rebuild with condenser and evaporator.

I will take a look at the airflow again. The fan shroud is intact, but there is quite some space between the radiator and condenser. On the driver side, there are some kind of plates on the side between the rad and condenser, but on the passenger side there is a space where you can look between them. Propably not good for airflow, but it doesn´t look like something is missing there from factory, guess I have to fabricate a plate..

Topic electric fans has been on my mind for quite a long time. If the rad is leaking or the stupid clutch fan fails again (I had to order 3 clutches before getting one that actually worked), I thought about swapping to an aluminum rad from champion radiator or something like that, with a nice set of electric fans. My mechanic said if we do that, we could also install an additional pressure switch in the high-side port at the back of the compressor (where on the newer modelyears the cutout switch would be) and wire it in the radiator fan harness to make them run when the AC needs it, while staying off on the highway. I don´t want any additional switches under the dash, stuff like that has to work automatically as if it came from the factory.

Mechanic said another option could be to use the R12 replacement R12A like the Duracool 12A or one of the thousand names for the same stuff. Pressures would be more like the original R12 and can work better with the lower airflow of the original system. Since the car was already converted to 134A we stayed with that.

But thats another big project for the future since none of those parts are available here, everything needs to be ordered from the US and we basically have no autoparts shops like you do where I can just drive and buy or order everything I can dream of.
Germany is not the country for carlovers like me.

[JohnHere]

I am surprised that you mentioned the 3.3lbs could possibly be a bit low for the charge. While doing research, I found the GM retrofit guide with that formula: R12 charge x 0.9 - 0.25lbs = R134a charge. In my case, that would be 2.9lbs.
I trusted my mechanic who said that from his experience, these GM systems tend to like a bit more charge and we went with the 3.3lbs. With that noise from the ac, I thought the system is maybe overcharged and whenever I sit at a stoplight for a longer time, I shut the AC off if its hot outside to prevent any damage. Don´t know what can happen if I leave it on with that noise..

The reason I mentioned the possibility of the charge being a little low is because inadequate refrigerant could be a reason for the noise you're hearing. Interestingly, for the 1985-1988 model years, the specification that I have says 56 ounces net weight (3.5 pounds) of R-12; and for the 1989-1990 model years, 44 ounces net weight (2.75 pounds) of R-12. But those specs are for U. S. vehicles. If you have an under-hood decal that says 3.5 pounds, always go by the decal for, in this instance, a baseline amount of the original R-12. The decal supersedes any other data. You didn't mention specific pressures, but we presume that the shop was happy with those as well.

I will take a look at the airflow again. The fan shroud is intact, but there is quite some space between the radiator and condenser. On the driver side, there are some kind of plates on the side between the rad and condenser, but on the passenger side there is a space where you can look between them. Propably not good for airflow, but it doesn´t look like something is missing there from factory, guess I have to fabricate a plate..

Instead of fabricating a plate, you might be able to use some peel-and-stick foam insulation from the local home center for sealing any gaps, like the kind of insulation commonly used to close openings around the perimeter of a room air conditioner.

If it is hot, the compressor does not cycle off, at least at idle. With slow driving, I can hear it cycle from time to time, so I guess it cannot be undercharged badly. If its cold and I use the Defrost option to clear the windscreen from fogging up, the clutch cycles often. Normal behaviour as I understand.

It's normal behavior. The clutch will cycle to keep the evaporator at the right temperature, preventing it from icing-up and blocking airflow.

Topic electric fans has been on my mind for quite a long time. If the rad is leaking or the stupid clutch fan fails again (I had to order 3 clutches before getting one that actually worked), I thought about swapping to an aluminum rad from champion radiator or something like that, with a nice set of electric fans. My mechanic said if we do that, we could also install an additional pressure switch in the high-side port at the back of the compressor (where on the newer modelyears the cutout switch would be) and wire it in the radiator fan harness to make them run when the AC needs it, while staying off on the highway. I don´t want any additional switches under the dash, stuff like that has to work automatically as if it came from the factory.

That certainly could be done.

Mechanic said another option could be to use the R12 replacement R12A like the Duracool 12A or one of the thousand names for the same stuff. Pressures would be more like the original R12 and can work better with the lower airflow of the original system. Since the car was already converted to 134A we stayed with that.

That's good, staying with R-134a. On this Forum, we follow US-EPA guidelines on refrigerants and don't comment on or recommend any alternatives, which usually contain flammable hydrocarbons.

But thats another big project for the future since none of those parts are available here, everything needs to be ordered from the US and we basically have no autoparts shops like you do where I can just drive and buy or order everything I can dream of.

Meanwhile, I'd say enjoy your "cool" vintage Chevy. If something breaks in the future, you can address it at that time.

[freakyhead94]

Hello again,

Another problem with my AC, actually a different one, but also a noise, so the title matches. If you would like me to open a new thread, I will do so. But I thought adding it to this with all the background info what was done to the system would be nice.

Since temperatures were reaching 88°F this weekend, I took my chevy for a ride to test the AC with the new fanclutch. Seems to work pretty well, minimal difference between slow and fast driving with the AC. The real test for the original noise in this thread will follow when it gets really hot.
But: the compressor got pretty noisy. Since I am pretty sensitive to noises, I am sure that the compressor was not that loud before. With the hood closed and AC on, the compressor is almost louder that the engine. I dont have any flowmaster or special exhaust on, so yes the engine is kinda silent and smooth, but standing next to the car, the sound from the engine bay sounds like something is rattling apart.

I made 2 videos, 1 with the AC off where there is no weird sound: https://youtu.be/Be4ANuKJemo?si=ue8jdCSt_frHs_1g

And 1 video with the AC running: https://youtu.be/kwECEAaSwL4?si=TxIEf6aWUOfmgTyb

This sounds like some scraping of metal on metal or a bearing, something like that. I also noticed the belt tensioner vibrating with the AC on, maybe thats normal due to the pulses from the compressor.

I read several times that a loose belt or weak tensioner can make noises like that, so I took my 1/2" ratchet, sticked it in the tensioner and tensioned the belt by hand with the engine and AC running, absolutely no difference with the noise.

Is this noise "normal" with a R4 compressor? Many people say, they are always loud. But again, I am sure this noise was not there when I got the car. Or could this be a failing compressor clutch instead of the compressor itself?

Best regards
Felix

[JohnHere]

No need to open a new thread.

I've viewed and listened to your two videos several times during the last few days, and I don't think the compressor is all that noisy for an R4 lasting 35 years. After all, we all start to get a little noisy with creaky joints, and so on, as we age

As compressors go, the original one in your car is old, but the vehicle has only ~45,000 miles on it, which means that the compressor probably doesn't have too much wear on it. The problems that might develop sooner or later is a leaky shaft seal or a leaky o-ring at the case separation. In those cases, I would simply replace the compressor with a new one at that time.

I recall your mentioning that the system is cooling better now that you've replaced the fan clutch. Thinking about this for a while, I would leave it alone until the system shows signs of failing to cool sufficiently.