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Any A/C gurus out there?

NskLJ

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I didn't see anybody presenting the accumulator as something other than what it is. But on that, containing a dessicant makes it an accumulator-dryer.

Plenty of systems don't have accumulators, in fact they're not actually used very often in comfort cooling AC applications where the load and operating conditions are fairly stable. Where you see them is primarily in automotive where there is a fixed expansion device and loads vary from 100 ambient with high humidity, down to the depths of winter when the defogger is on. They're also used a lot in refrigeration which experiences large load shifts when portions of the system enter and exit defrost cycles.

Sounds like your an hvac guy. I was going to move my A/C unit across the yard and bury the lines and the recommendation was to install a accumulator to prevent liquid slugging of the compressor due to liquid accumulating in the lines underground.
 

Mikee024

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First off, yes, I know I should replace the dryer. So in the question below I know the answer is "replace the dryer" but also answering the question I'm actually asking will be much more helpful.

When I got my TJ the A/C Schrader valves were bad so the system was down/out on refrigerant. I replaced them and now it will hold vacuum without dropping over the course of a week or so.

My two questions then are;
1) Using the AutoZone rental manifold gauges and vacuum pump I can pull about 26" Hg and that's where it sticks. But it should pull 29 right? So is the 26 because of bad free loaner tools, a system fault, a bad part? Again, after I disconnect the vac pump and gauges the system will hold at the 25-26" range so it's not dropping like it has a leak.
2) Consider me a cynic, but before I spend the money to replace the dryer I'd like to run some UV dye through the system with new refrigerant to verify if, in fact, the system does maybe have a miniscule leak anywhere. What will be the impact on the system if I go ahead and send it with the existing dryer? Air won't be as cold? The streams will cross and my Jeep will implode?

Thanks for any input!

You don't need dye. You simply need to test it properly. I go to dye once I know I have a leak (through testing) and need help confirming the location of the proven leak.

If you are holding a vacuum after an hour then you don't have a leak. That might be overkill to some, but I know for a fact I'm holding a vacuum by being patient in that step.

Are you using a single-stage or two-stage vacuum pump? I've had to use a two-stage after a single stage didn't pull enough vacuum. I noticed that HF had a two-stage on the shelf of my local store, but I've never tested how good it is.
 

freedom_in_4low

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Sounds like your an hvac guy. I was going to move my A/C unit across the yard and bury the lines and the recommendation was to install a accumulator to prevent liquid slugging of the compressor due to liquid accumulating in the lines underground.

16 years in AC and refrigeration equipment design, all commercial and industrial but a little of everything whether it be cataloged or completely custom, process and data centers, comfort, refrigerated warehouses and lately a lot of supermarket.

Good call on at line burial thing. The liquid will find the coolest parts of the system so there would almost certainly be times where that buried line had a bunch of liquid just waiting for the compressor to come on and suck it in. I've seen a lot go into preventing and surviving liquid into a compressor...in fact all of our stuff includes heaters in the compressor so its always the warmest place in the circuit.

In my last job I was a system design engineer on rotary screw compressor chillers. I was working on integrating a new 150 ton compressor and variable speed drive and one of the tests I did was to ice the compressor overnight with the compressor heaters off to get liquid to settle inside it until it was completely full, and then hit the go button. The expectation was that the drive recognized the pattern in the compressor input current and shut it down within fractions of a second. Fortunately it passed, but we did that test last just in case as that custom cast and machined prototype cost about $80k and took months to get made. 😬

Years before that i visited the R&D facility of a major compressor manufacturer and saw where they were doing an accelerated life/liquid injection test on a new scroll compressor. It has been running non stop for months and every few minutes they would hit it with something like 20 pounds of straight liquid. All I saw was about 2 inches of compressor housing exposed in a huge ball of ice. None of them like liquid but scrolls seem to take it better than screws, at least partially because their housings act as a built-in accumulator.
 
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Mikee024

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Sounds like your an hvac guy. I was going to move my A/C unit across the yard and bury the lines and the recommendation was to install a accumulator to prevent liquid slugging of the compressor due to liquid accumulating in the lines underground.

We used to run a toilet paper dryer in our shop air lines for the die grinder and sandblaster. I installed a condenser and dryer in the air lines for our CNC. Never had any problems with our setup.

FWIW, I also built a surround around the large air compressor using horse mats suspended from iron pipe bolted into the wall that suspension wire (to help the iron pipe handle the weight), then had a 1" mdf board on top. It made a world of difference in our quality of life since the shop office had little insulation.
 
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NskLJ

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You don't need dye. You simply need to test it properly. I go to dye once I know I have a leak (through testing) and need help confirming the location of the proven leak.

If you are holding a vacuum after an hour then you don't have a leak. That might be overkill to some, but I know for a fact I'm holding a vacuum by being patient in that step.

Are you using a single-stage or two-stage vacuum pump? I've had to use a two-stage after a single stage didn't pull enough vacuum. I noticed that HF had a two-stage on the shelf of my local store, but I've never tested how good it is.

The compressor shaft seal is where the dye comes in handy, the shaft seal may not leak when it is not running. That’s why I suggested removing the clutch after running the dye. This has been my experience.
 
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Mikee024

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The compressor shaft seal is where the dye comes in handy, the shaft seal may not leak when it is not running. That’s why I suggested removing the clutch after running the dye. This has been my experience.

I was replaying to his quote thinking he was going to use dye to find a a general leak.

However! I didn’t know about the shaft seal and that dye can come in handy there. Thanks for sharing that helpful info 😀
 

NskLJ

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I was replaying to his quote thinking he was going to use dye to find a a general leak.

However! I didn’t know about the shaft seal and that dye can come in handy there. Thanks for sharing that helpful info 😀

I usually only use dye on problem leaks but he specified he wanted to use it. One problem with automotive A/C there is many places for leaks to occur. It sounded like he didn’t really know the history of the system. I wrote up what I would do in his situation. I left the auto industry 18 years ago. I worked for one one of the big three and the manufacturer had us stop replacing the accumulator dryer with every repair. The manufacturer said it wasn’t necessary evacuating the system was enough to remove the moisture from the desiccant. Now weather this was just a roll off the dice to cut costs I don’t really know but when they pay the bill they can dictate the repair.
 

Mikee024

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I usually only use dye on problem leaks but he specified he wanted to use it. One problem with automotive A/C there is many places for leaks to occur. It sounded like he didn’t really know the history of the system. I wrote up what I would do in his situation. I left the auto industry 18 years ago. I worked for one one of the big three and the manufacturer had us stop replacing the accumulator dryer with every repair. The manufacturer said it wasn’t necessary evacuating the system was enough to remove the moisture from the desiccant. Now weather this was just a roll off the dice to cut costs I don’t really know but when they pay the bill they can dictate the repair.

I was going to ask your opinion on how critical it is to pull vacuum immediately after installing the dryer (I believe your post answered my question).
 

NskLJ

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I was going to ask your opinion on how critical it is to pull vacuum immediately after installing the dryer (I believe your post answered my question).

Orfice tube systems are not sensitive to internal moisture as expansion valve systems due to no moving parts. When I would do systems I would make sure to install the dryer and at least get the system sealed the same day if not charged. I life and work within 5 miles of the ocean so the moisture comes in pretty thick at night.
 
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Mikee024

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Orfice tube systems are not sensitive to internal moisture as expansion valve systems due to no moving parts. When I would do systems I would make sure to install the dryer and at least get the system sealed the same day if not charged. I life and work within 5 miles of the ocean so the moisture comes in pretty thick at night.

Thanks for sharing this info.

I got my system evacuated the same afternoon I replaced the dryer, and I hoped that would be fine since I lived in AZ (but I wasn't really sure).
 

VadeerHunter

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Here's one for you in a/C 101, your TJ does not have a dryer if it's factory air ! It has a accumulator which is not a dryer, they do 2 completely different things. You need to replace the accumulator and flush that system and check that orifice tube and vacuum and fill with refrigerant and pag oil.

Bingo. A Nitrigeon flush is a very good move.
 

NskLJ

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16 years in AC and refrigeration equipment design, all commercial and industrial but a little of everything whether it be cataloged or completely custom, process and data centers, comfort, refrigerated warehouses and lately a lot of supermarket.

Good call on at line burial thing. The liquid will find the coolest parts of the system so there would almost certainly be times where that buried line had a bunch of liquid just waiting for the compressor to come on and suck it in. I've seen a lot go into preventing and surviving liquid into a compressor...in fact all of our stuff includes heaters in the compressor so its always the warmest place in the circuit.

In my last job I was a system design engineer on rotary screw compressor chillers. I was working on integrating a new 150 ton compressor and variable speed drive and one of the tests I did was to ice the compressor overnight with the compressor heaters off to get liquid to settle inside it until it was completely full, and then hit the go button. The expectation was that the drive recognized the pattern in the compressor input current and shut it down within fractions of a second. Fortunately it passed, but we did that test last just in case as that custom cast and machined prototype cost about $80k and took months to get made. 😬

Years before that i visited the R&D facility of a major compressor manufacturer and saw where they were doing an accelerated life/liquid injection test on a new scroll compressor. It has been running non stop for months and every few minutes they would hit it with something like 20 pounds of straight liquid. All I saw was about 2 inches of compressor housing exposed in a huge ball of ice. None of them like liquid but scrolls seem to take it better than screws, at least partially because their housings act as a built-in accumulator.

Sounds like a very interesting job you have. My life took a different path, I did not stay in school been a auto mechanic most of my life. Last 18 years I have been down at the LA/LB port doing maintenance. Worked in a reefer shop for a while. Those scroll compressors take a beating and keep going. We had 72 cranes delivered to our terminal with 5 a/c systems per crane not sure the size (3-5 to my estimate) with no filters or dryers installed. (China go figure) that was a time consuming and expensive retrofit.
 
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freedom_in_4low

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Sounds like a very interesting job you have. My life took a different path, I did not stay in school been a auto mechanic most of my life. Last 18 years I have been down at the LA/LB port doing maintenance. Worked in a reefer shop for a while. Those scroll compressors take a beating and keep going. We had 72 cranes delivered to our terminal with 5 a/c systems per crane not sure the size (3-5 to my estimate) with no filters or dryers installed. (China go figure) that was a time consuming and expensive retrofit.

it's been more interesting than I thought it would be at 18. When I told my dad I had selected Mechanical Engineering as my college major he asked me what I wanted to do with that. I told him I'd love to go work for a car manufacturer and work in powertrain or suspension design, but "worst case" I'd end up designing refrigerators. :ROFLMAO: :ROFLMAO: :ROFLMAO: Once I got deeper into school I found fluid mechanics and heat/energy transfer to come much more naturally to me than statics and mechanical components, so it ended up being a good fit and I've had more freedom, less stress, and better work/life balance than I would have had with an automaker.
 
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f22beaver

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I never knew air conditioning would be my most popular post. 🤣

Status update. I went ahead and swapped in a new accumulator. I pulled 30 in of vacuum and it held for 72 hours while I was on a work trip. Now it takes refrigerant but the compressor keeps shutting off before it will take in all 20 oz. I would say I have something around 12 oz in it and it is blowing extremely cold air but it just won't pull in more refrigerant. Our ambient temp today is 60°. Is it possible the car doesn't want the compressor on because it's too cold outside? Where is the sensor that it's reading temp from, and can I trick it with a heat gun?

The high pressure will only get to about 150 psi then the compressor shuts off.
 
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f22beaver

f22beaver

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Fwiw I've got 63 ambient and 48 at the vent.

Oh, nevermind!!!! Just went and drove it hard. Came home, it took the rest. Compressor stays on. The FSM doesn't recommend pressures at 60F but I'm at 30 low and 150 high which jives. Oh, and now it's 39 at the vent. 🥶🥶🥶☃️⛄❄️🌨️

PXL_20220923_182337614.jpg
 
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freedom_in_4low

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starting from a truly empty system like that, if you added the correct charge by weight then I wouldn't worry too much about the pressures. The cycling you saw while charging is normal; when the charge is low the compressor pulls the suction pressure down below what's required to run, so the low pressure switch shuts it down until the pressure climbs back up.
 

Mikee024

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Fwiw I've got 63 ambient and 48 at the vent.

Oh, nevermind!!!! Just went and drove it hard. Came home, it took the rest. Compressor stays on. The FSM doesn't recommend pressures at 60F but I'm at 30 low and 150 high which jives. Oh, and now it's 39 at the vent. 🥶🥶🥶☃️⛄❄️🌨️

View attachment 361490

Before long you won’t need AC, but I’d still cycle the system every now and again to ensure seals stay lubricated.

I’m not sure if/where the cut off point is ambient temperature wise to safely run the system (or if that’s even a practical concern more most of us). @freedom_in_4low curious if u have any input on this.
 

freedom_in_4low

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Before long you won’t need AC, but I’d still cycle the system every now and again to ensure seals stay lubricated.

I’m not sure if/where the cut off point is ambient temperature wise to safely run the system (or if that’s even a practical concern more most of us). @freedom_in_4low curious if u have any input on this.

It'll run over the winter if you ever make use of the windshield defroster/defogger. Perk of the orifice tube type system is that the low side pressure and high side pressure will basically always have a healthy differential, so if the ambient gets cold enough, the high side pressure will be low, the low side pressure will eventually get low enough to shut it down on the low pressure switch. That being said, I have considered that they may have been counting on some of the heat gained through the uninsulated lines in the engine compartment, which I recently insulated. There's no other explanation I can find for putting 3 feet of 2-phase line (between the orifice and the evaporator) through an engine compartment.

In commercial-sized systems, a TXV or EEV is used which in extremely low ambient either will fail to control flow well enough to fully vaporize all the liquid in the evaporator, sending liquid back to the compressor, or it will open up to allow enough flow as not to have a safe differential across the compressor. Most of those compressors have a minimum differential to perform various functions such as being the motive force for internal lubrication (instead of an oil pump) or keeping rotors seated against their thrust bearings. Controls are integrated to protect the system from these scenarios.
 
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Mikee024

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It'll run over the winter if you ever make use of the windshield defroster/defogger. Perk of the orifice tube type system is that the low side pressure and high side pressure will basically always have a healthy differential, so if the ambient gets cold enough, the high side pressure will be low, the low side pressure will eventually get low enough to shut it down on the low pressure switch. That being said, I have considered that they may have been counting on some of the heat gained through the uninsulated lines in the engine compartment, which I recently insulated. There's no other explanation I can find for putting 3 feet of 2-phase line (between the orifice and the evaporator) through an engine compartment.

In commercial-sized systems, a TXV or EEV is used which in extremely low ambient either will fail to control flow well enough to fully vaporize all the liquid in the evaporator, sending liquid back to the compressor, or it will open up to allow enough flow as not to have a safe differential across the compressor. Most of those compressors have a minimum differential to perform various functions such as being the motive force for internal lubrication (instead of an oil pump) or keeping rotors seated against their thrust bearings. Controls are integrated to protect the system from these scenarios.

I would be pretty butt hurt if I had to remove the insulation in the winter time lol.

Thanks for the in-depth response. I learned some things and learned even more about how I need to learn more things. (sounds like a Rickyism from TPBs)
 
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