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SteveF
09-26-2012, 08:58 PM
OK, a couple years ago my Kenmore refrig was low on freon so the tech added a tap and put some freon in. Told me to add some more (R-134a) if the problem returned. No problem to add some in but do we have any techs here who know what pressure reading I should get when the correct amount of freon is added? Searching the internet gives a bunch of numbers around / under 10 PSI but obviously not from people who have any first hand knowledge or training. Anything bad happen when too much is added?

Thanks.
Steve

Sparky_NY
09-26-2012, 10:39 PM
Yes, lots of bad things happen with a overcharge. R134A in a refrigerator should be below zero psi pressure, about zero to minus 4 would be about right. Technique is very important !!! If you let any air into the system bad things are going to happen. Because it runs below zero psi, you want to connect and disconnect your gauge lines with the unit off and after sitting a few minutes so that the pressure equalizes and comes above zero. The air has to be bled from the hoses also so that it does not enter the system. Also, I would expect the TOTAL charge to be in the area of 12oz or so of R134A, that is not very much! Small refrigeration units like this have what is known as a critical charge, standard practice is to weigh it in from empty but topping off is done by experienced techs at times.

Small refrigeration units are the most difficult to work on.

atty
09-27-2012, 06:50 AM
[QUOTE=Small refrigeration units are the most difficult to work on.[/QUOTE]

That's an understatement to be sure. One of the key elements of small unit servicing is patience. You have to introduce an amount of charge, then wait for things to stabilize. They don't react quickly like auto A/C or home A/C units.

SteveF
09-27-2012, 08:52 AM
Yes, lots of bad things happen with a overcharge. R134A in a refrigerator should be below zero psi pressure, about zero to minus 4 would be about right.

OK, I'm confused. So, the blue gauge is measuring vacuum, not pressure? So why does the number go up when freon is added? If the line with the tap is running with a vacuum I'm guessing excess freon has to be vented with the refrigerator NOT running and after things stabilize. How long should that take? If it helps the data plate shows this refrig holds 9 oz.

Steve

Sparky_NY
09-27-2012, 09:22 AM
OK, I'm confused. So, the blue gauge is measuring vacuum, not pressure? So why does the number go up when freon is added? If the line with the tap is running with a vacuum I'm guessing excess freon has to be vented with the refrigerator NOT running and after things stabilize. How long should that take? If it helps the data plate shows this refrig holds 9 oz.

Steve

The blue gauge is for the "low side" or suction side of the compressor. Depending on the system, that suction line can run anywheres from a vacuum to over 100psi. The actual blue gauge reads both above zero (pressure) and less than zero (vacuum). Notice the numbers on the gauge less than zero? Most gauges are marked down to 30 inches of vacuum and up to 300psi pressure. The gauge can swing both ways of zero.

As a example lets say a refrig is very low on freon and the gauge reads 20 inches of vacuum, as freon is added the pressure will increase, first to 10 inches of vacuum, then to zero psi then continuing to +5psi, then +10psi and so on. It will swing from vacuum, through zero and then to pressure.

Final readings and adjustments MUST be taken after the system has cooled down close to its normal operating temperatures othewise you will not get proper readings.

In the case of R134a in a low temp unit (refrigerator), yes it runs at less than zero pressure, just slightly less.

Yes, excess freon would have to be vented with the system off, you only have to wait maybe 2 or 3 minutes after shutting it off and you will see pressure on the blue gauge. The 9oz nameplate charge is indeed a tiny one, its going to be very critical about the freon charge. This is the reason the charge is most commonly weighed into a empty system on tiny units like this.

As a further note, its the freezer temp you want to monitor for performance, not the refrigerator side. Working properly it should be between zero and minus 15 degrees in the freezer.

Small units like this can give even Pro's headaches in servicing them. The odds of you getting into trouble are quite high.

SteveF
09-27-2012, 11:11 AM
Small units like this can give even Pro's headaches in servicing them. The odds of you getting into trouble are quite high.

LOL. And that is exactly why I'm asking for help from those who might know how these things work!!

Your explanation is excellent. I'll go take some vacuum readings and see what I get.

Thanks.
Steve

SteveF
10-04-2012, 10:55 AM
Sparky

Update: Had a guy I know who does commercial and residential HVAC systems come over and he added some more freon and it was reading 12 PSI positive pressure. He said the extra pressure was no problem and it would just sit in the accumulator. Then I talked to a retired refrigerator tech and determined that knowledge of large HVAC systems does not necessarily apply to refrigerators since he also said overpressure is bad. :mad:

Based on your info I decided to remove some of the freon and it now reads 3 PSI positive pressure while running. Didn't seem like I took out much to get it from 12 to 3 so I'm concerned about taking any more out since the retired guy also confirmed getting air into the system is bad. Right now the refrig is no longer making any gurgling sounds or other strange sounds it didn't used to make after shutdown and with the temp control in the middle position the freezer compartment is at 20 degrees F. My belief in not messing with things that are working is starting to kick in.

Is this couple pounds of overpressure a problem and what parts might get damaged. Note that this whole drill is because the refrig is very slowly leaking freon (last top up was 3 years ago) and the problem will be going away over time.

Thanks for the help.
Steve

Bob Pekny
10-04-2012, 11:07 PM
Steve, You are getting close. In the old days we used to put in a bit to much freon, (R-12) back then, and then we would watch the frost line , when a unit is a little overcharged the suction line will frost up when the system is running. You don't want it frosting all the way back to the compressor. Sweating is ok but not frosting. Then we would let a bit of freon out and watch the frost line retreat back into the box. We kept this up a little at a time until the frost line just disappeared. Small friges don't usually have accumulators and are quite sensitive to the exact charge. Also when you are done the freezer temp will be lower. When it is back working and the compressor has cycled off for a while check your line tap with bubble soap for leaks. They often are a source of leaks.

SteveF
10-05-2012, 06:36 AM
I realize that I'm close, and the refrig is working acceptably well. Right now I know there is no air in the system and I'm concerned that I might accidently introduce some as I approach the vacuum state on that low pressure line. So, the question that I'd like to answer is, is there any chance of damaging something if I just let this overcharge problem resolve itself as it slowly leaks out or do I need to remove a little more freon?

Steve

Doozer
10-05-2012, 07:02 AM
I have heard of this method before.
It seems really good way to get the correct charge.
Too bad the hoses were not clear and you could see liquid or gas.

--Doozer

Bob Pekny
10-05-2012, 11:52 PM
If your suction line is not frosting back to the compressor and is not sweating so much the side of the compresssor near the suction line is sweating you probably will not damage anything. It will probably will run a bit more and use a little more electricitry. The suction line accumulator your friend mentioned is used on larger systems to "boil away" any liquid freon before it gets back to the compressor. What will damage a compressor is trying to pump any liquid. This is why you always keep your freon can upright when you are charging. In my very early days I once toasted a car a/c compressor when I didn't notice the freon can had tipped over.

Is your fridge working well enough to be cycling on and off on its thermostat?

Jim Hubbell
10-06-2012, 12:28 AM
+1 on the frosting the compressor. The loside line should just sweat at the end of the comp. run cycle. It is my understanding that charging 134A MUST be done with liquid only. If the refrigerant fractionates the specifications are altered. R-12 etc. no problem with vapor charge.


Edit: atty is correct. I confused R134A with a different refrigerant. Vapor chg. is OK.

atty
10-06-2012, 02:57 PM
Actually 134a is pure compound, not a blend, so fractionating is not a problem.

dwleo
11-24-2015, 01:27 PM
Hi,
I realize that this thread is very old but I am curious as to the statement of keeping the can of 134A upright when, on the can it states to invert it.
Can someone shed light on this?
Thanks.

Juiceclone
11-25-2015, 01:50 PM
again A+ on the old school "watch the frost/cond line". Learned that 50 years ago and still useful. As far as can upright or upside, liquid charging is quicker but "could" result in the compressor intake of liquid and "slugging" .... plus when you disconnect the hose you might get an unpleasant surprise. ....wear safety glasses......I'm surprised at the casual sale and use of R134 particularly in auto a/c. Seems like they just throw more and more in there. It's a good thing the car computer keeps track of pressures and limits high side (disengages compressor clutch). There's no such safety on most domestic ref systems. :>))
Whenever I use a piercing tap to service a system, I use two. One low side and one high side. I like to KNOW what's going on in there...

Doozer
11-25-2015, 02:45 PM
When a system calls for 134a, I actually use propane to fill it.
It seems to mix fine with 134a to top off a charge as well.
Pressures will be slightly higher, but no problem.
The system will cool better using propane as well.

--Doozer

dwleo
11-25-2015, 04:04 PM
Here is where I am coming from.
I started with a Danby mini and converted it to a single tap kegerator. No big deal. Then added another tap and had to drastically alter the innards to fit two mini kegs and the co2 bottle. From there I wanted to add a wine tap using nitrogen so I built my own fridge. Once it was altogether made out of 2x2's and foam panels. The co2 and nitrogen tanks were in their own compartment at the back of the unit. Cedar on the outside, tile on top and it looked great. As I inadvertently cut the lines when disassembling the Danby, I had to braze/solder the lines back together and do the vacuum/recharge dance. I plugged it in and let it come to temp and all was right. Due to a series of incidentals, the protective cap came off the starter/capacitor, line shorted and long story short - I learned just how flammable R134A really is. Since then I reinstalled a compressor, soldered/brazed the lines and made sure the cap was locked in place. I am having a hell of a time to get the charge amount correct. It always seems to work at first - the compressor would get warm, the line into the fridge would get cool, gauge reads about 1-3 psi and the compressor is running nice and quiet. No clicks, gurgling or anything. I kept a probe for an electronic thermometer inside and monitored the temp. The temp would slowly fall - nowhere near as fast as I thought it should - until, after about 3 hours it reversed itself. No longer cooling, it started to warm up inside. It had dropped to only about 48 deg F at its coolest.
The compressor had gotten REALLY hot at this point so I just unplugged it. By really hot I mean your finger could only touch it and not remain on it. What, in your opinion can a layman like myself do to get this working. I had tried to use a complete system from another mini fridge but cut into the line as well.

Juiceclone
11-25-2015, 05:27 PM
too many variables to say. Try finding a vending machine, like an old pepsi/coke or food and you will find a complete "package" unit that you can remove without breaking into the system. Adapt/mod to your use. They are built to last, and usually are repairable.

dwleo
11-25-2015, 10:28 PM
That's all well and good but I can't remember the last time a unit like became available if ever.
Meanwhile I still have this problem.
Maybe it would be better if I knew the definitive answer to:

1. What are the tell tale signs of an overcharged system?
and
2. What are the tell tale signs of an undercharged system?

Anyone?

Thanks.

wmgeorge
11-26-2015, 09:57 AM
That's all well and good but I can't remember the last time a unit like became available if ever.
Meanwhile I still have this problem.
Maybe it would be better if I knew the definitive answer to:

1. What are the tell tale signs of an overcharged system?
and
2. What are the tell tale signs of an undercharged system?

Anyone?

Thanks.

To do the job right you need both a high side and low side reading. Line tap piecing valves all leak, some more than others. If you can't solder in proper Schrader valve fittings you should not be messing with trying to do refrigeration work. R134a and moisture do not play well and the POE oil absorbs water and makes a mess internally in the system, clogging metering devices and ruining compressor valves.

Pressures. Get a P-T chart for refrigerants and then do some reading in a real book, not from posts on the internet. Generally speaking you want the low side temperature 10 degrees less in a refrigerator (converted to pressure) than the evaporator temperature. Example. you want a -10 Deg F evaporator then the R-134a target temperature should be -20 Deg F converted to pressure.... about a 2 - 4 inch Vac.
With a low side reading only, IF you have a plugged or partly plugged metering device (cap tube in this case) pretty common with DIY service people because of the moisture introduced into the system then you can have a very low, low side reading and introducing More refrigerant into the system causing dangerous high side pressures. Without a gauge on the high side you will never know.

Link for some more info> http://www.achrnews.com/articles/122078-using-the-p-t-chart-to-diagnose-refrigeration-ac-system-problems or here > https://www.johnstonesupply.com/storefront/store92/pressure-temperature-chart.ep

Tom S
11-26-2015, 11:35 AM
To do the job right you need both a high side and low side reading. Line tap piecing valves all leak, some more than others. If you can't solder in proper Schrader valve fittings you should not be messing with trying to do refrigeration work. R134a and moisture do not play well and the POE oil absorbs water and makes a mess internally in the system, clogging metering devices and ruining compressor valves.

Pressures. Get a P-T chart for refrigerants and then do some reading in a real book, not from posts on the internet. Generally speaking you want the low side temperature 10 degrees less in a refrigerator (converted to pressure) than the evaporator temperature. Example. you want a -10 Deg F evaporator then the R-134a target temperature should be -20 Deg F converted to pressure.... about a 2 - 4 inch Vac.
With a low side reading only, IF you have a plugged or partly plugged metering device (cap tube in this case) pretty common with DIY service people because of the moisture introduced into the system then you can have a very low, low side reading and introducing More refrigerant into the system causing dangerous high side pressures. Without a gauge on the high side you will never know.

Link for some more info> http://www.achrnews.com/articles/122078-using-the-p-t-chart-to-diagnose-refrigeration-ac-system-problems or here > https://www.johnstonesupply.com/storefront/store92/pressure-temperature-chart.ep

Bang on. I'd be more worried about a blockage of the cap tube than over/under charge. If it's building up over time I'm guessing there is moisture in the system that is turning into ice and blocking the cap tube. If you watch your gauges the suction pressure should drop really low at this point, but because the flow of refrigerant is mostly blocked there is not much heat transfer going on. Depending on how you brazed (with or without nitrogen), there could also be some carbon floating around.

If you're serious about this get gauges on the low side and the high side, flush the system out with nitrogen, triple vacuum (break with nitrogen), and vapor charge slowly to find the critical charge for that cap tube setup.

One more thing - R-134a is not flammable. Manufacturers in North America are just starting to be allowed to use flammable refrigerants in commercial and household applications - namely propane and isobutane. Something fishy is going on if your 'R-134a' is going up in smoke.

dwleo
11-26-2015, 11:52 AM
Interesting reading. Thank you.
I think I am now more confused than ever.
Still haven't got a definate answer to the question of the R134A can. Upright or inverted?

Tom S
11-26-2015, 11:58 AM
Upright, unless you want to replace the compressor again.

wmgeorge
11-26-2015, 12:54 PM
Upright, unless you want to replace the compressor again.

Tom correct answer.... But if your an experienced service person you Can change liquid into the low side. Done it many times myself but it has to metered in very carefully knowing you can slug a small compressor and kiss It goodbye in a heartbeat. Answer for online DIY people, no always charge vapor, unless its a blended refrigerant.

The only refrigerant I know that's flammable is propane, the oil however in any system can and will burn.

dwleo
11-26-2015, 07:26 PM
OK. All good information.
What is the difference between R134a and R22a?

im#2
11-26-2015, 10:52 PM
WOW this rehashed discussion all came at a bad time as I have service guard with the gas company here in Colorado and my big expensive refrigerator has just crapped out , he said it has a blockage in the coils and impossible to find or get it out so, I read this with interest but not much I can do to fix so guessing I will get us a new one for Christmas early for both of us.

Tom S
11-26-2015, 11:00 PM
R-12 is a CFC refrigerant and has a high ozone depletion (ODP) and global warming potential (GWP). The two chlorine atoms cause the ozone depletion.

It was replaced by R-22, a HCFC which has a lower ODP and a high GWP. It has one chlorine atom instead of two, so less ozone depletion.

It was replaced by R-134a and R-404a (at least in refrigeration, I don't keep up on the AC side of the business), which are HFCs that have a ODP of 0, but still have higher GWP's. No chlorine atoms.

In the next number of years you'll begin to see the HFC's phased out and replaced by Hydrocarbons (propane and isobutane) in smaller systems, HFO refrigerants in medium sides systems and AC units, and Carbon Dioxide systems in large systems.

The first three generations of refrigerants (R-12, R-22, R-134a/R-404a) had relatively small differences in pressures and temperature ratings, so some of them could be used as drop-in replacements and some required small changes to equipment. The HFO refrigerants will be somewhat similar in this regard. Changing to Hydrocarbons and Carbon Dioxide systems will require large changes in equipment and operating parameters, but has the benefit of increased energy efficiency greater than that seen by the HFO refrigerants.

wmgeorge
11-27-2015, 12:11 PM
Good answer Tom but I believe R134a was intended to replace R12. Its not a true drop in replacement because the oil needs to changed POE for R134a. R22 was and is used for air conditioning and then for medium and low temp refrigeration. R22 has a problem with oil return in the refrigeration field, especially in low temp applications. There are drop in replacements for R22 that are CFC free. R410a is now also used in the air conditioning field, but its not a drop in replacement and runs at much higher pressures.

However as you and some others have pointed out propane and butane can be used to directly replace R12. That use is Not approved by the EPA in this country but I understand its widely used in Europe but I could be educated differently if that not true. The problem with flammable refrigerants as propane is they burn, and that's a big duh. There are fears that a car AC unit charged with propane could be a hazard in a accident. More so than a tank full of gasoline??

Tom S
11-27-2015, 12:33 PM
However as you and some others have pointed out propane and butane can be used to directly replace R12. That use is Not approved by the EPA in this country but I understand its widely used in Europe but I could be educated differently if that not true. The problem with flammable refrigerants as propane is they burn, and that's a big duh. There are fears that a car AC unit charged with propane could be a hazard in a accident. More so than a tank full of gasoline??

Europe is ages ahead of North America when in comes to hydrocarbons. They were commonly used in early refrigeration systems, but were regulated out because of safety concerns. We're just developing safety standards, and can only have a 150g maximum charge of a hydrocarbon. Hydrocarbons are less dense than f-gasses, but there are definite limits to unit size.

It's a bit crazy when you think that a store can only buy a small refrigerator using propane because of explosive concerns, but can also sell bottles of propane for camping a couple aisles over and no one bats an eye...

wmgeorge
11-27-2015, 01:23 PM
And there are cars and trucks on the road today powered by LNG or Propane, so how is a propane charge in a mobile AC more dangerous? One reason its called dangerous is because Dupont and other refrigerant makers can not control the price.