Refrigeration Regassing (R600a)

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Introduction

The aim of this guide, is to give some tips on re-gassing a refrigeration appliance, it is based on me doing so with a Hotpoint FZ150 freezer that uses R600a refrigerant.

WARNINGS

I am not, and do not profess to be a refrigeration engineer, I have gained some knowledge of this simply be reading information online, and from a number of YouTube videos posted by a variety of people. Please be mindful of this before attempting to work on any refrigeration appliances as a result if reading this.

The refrigerant I am going to describe is R600a, which is Isobutane, which is flammable, so extreme care needs to be taken when handling this.

I performed this recharge in my garage, with the rear door open and the roller-shutter door partially open to ensure there was ample ventilation, when venting out the existing R600a in the system, I also powered off the garage prior, to minimise any chance of any electrical sparks from switches etc.

Did I mention it was highly flammable?

There have been cases in the UK of refrigeration appliances using R600a exploding and causing damage to property, in my case, the freezer is going to live in a slightly drafty garage, so I am not particularly concerned about this, so if your appliance lives inside, you may wish to reconsider DIYing a repair on an appliance with flammable refrigerant.

Type of Freezer

In this case (Hotpoint FZ150) this is a frost free freezer that has a microprocessor controller using R600a refrigerant.

Symptoms

The freezer in question has a microprocessor controller, so it has some intelligence, so didn’t just sit there running the compressor 24/7 when it wasn't getting cold enough. If you have a simple freezer, this can happen, which can lead to compressor failure, so if the compressor is not running at all, then you need to check the thermostat is closing (this is another common fault) and if so, and there is power getting to the compressor, but it is not running, then the compressor has failed, and that is outside the scope of this guide.

What would happen on mine was after initial start-up it would run for a while, then flash the alarm light, and lock out, presumably to protect the compressor and to alert the user there is a problem. The temperature in the freezer didn’t get anywhere near freezing (and it started at about 10C as it was in the garage).

This is a frost free model, two common faults that would show this same sort of symptom are ice build-up that has not been melted during the defrost cycle restricting the airflow from the fan inside, or failure of the internal fan (We also have a Liebherr freezer that has had the iced up issue, with the Liebherr, it was not obvious there was ice build-up, as like the Hotpoint, the evaporator is all enclosed in a compartment at the top of the freezer, but a thorough defrost resulted in more water on the compressor dish, and then a working freezer.

As the freezer in question had been sat empty and turned off for over a week, icing up was not the problem here, and I could hear the fan was running before it cut out, which I confirmed by defeating the door switch, so the freezer thought the door was shut, so started the fan (there was a delay between the compressor starting and the fan starting, I am not sure if that is timed, or the controller sees a difference in temperature between the inside of the freezer and the evaporator, if the latter, then total loss of all refrigerant, which would mean no cooling at all, would cause the fan to not work either, so if the fan is not running on yours, and the condenser on the back is not getting warm, then this could be the problem, rather than a failed fan.

What lead me to believe my freezer was low on refrigerant, was the fact the compressor seemed to be running freely, but the evaporator (the part inside the freezer that gets cold) was only getting cold over the first 10cm or so, and the condenser coils on the back were not getting warm. On this model, there is door seal heating installed, which is achieved by the high pressure (hot) side of the compressor first going around a loop of pipe around the door seal, to keep that from icing up, then it goes out to the top of the condenser on the back of the freezer, I hadn’t noticed this before (the freezer was given to me broken so I didn’t know it had this) so I didn’t notice if this part was getting warm, but I suspect not very is the answer here.

Tools & Supplies

You will need the following to effect a recharge at a minimum.

1. Manifold gauge set

2. Cylinder of R600a refrigerant

3. Valve for the cylinder

4. Set of accurate scales suitable for the cylinder you buy.

5. A service valve on the suction side of the compressor


Ideally you would also have

6. A vacuum pump to evacuate the system

7. An accurate vacuum gauge

8. A cylinder of nitrogen to purge the system

9. A replacement filter/drier

10. Lokring connectors and appropriate lokring tool or brazing equipment.


In my case, I bought items 1-4 from eBay, and I used an old freezer compressor I salvaged as a vacuum pump – this is not really ideal, and is not suitable if your appliance has lost all of its refrigerant or you open it to the atmosphere by changing the filter/drier, a proper vacuum pump is necessary, and can be had for around £90 on eBay at the time of writing.

I didn’t have items 7-10, but as there was still some pressure in my freezer, I figured the system would hopefully be reasonably clean, and I could always recharge it again later if I did need to vacuum it down properly.

The freezer already had a service valve fitted, but if it didn’t, eBay had “line taps” available which would have served this purpose.

The manifold gauge set I bought had two valves and 4 ports (2 ports on the middle connection) and came with three hoses (blue, yellow and red) The hoses have one end totally open, and the other end has a small metal pin in the middle, to press schrader valves open (which the service valves on the freezer are, so disconnection of the hose automatically seals the valve closed to stop the refrigerant escaping)

Diagnosis

Firstly, I turned the freezer off, so the compressor was not running. The reason for this is, on an R600a system (and probably others) if the system is low on refrigerant, then the suction side will be pulling a vacuum, so if I connected a hose up with the compressor running, air in the hose would be pulled in, and would contaminate the system.

I connected the open end of the blue hose to the blue side of the manifold (with the blue valve closed), and the other end of the blue hose to the suction side of the compressor in the freezer. My freezer also had a service port fitted to the high side of the compressor, having this helps with diagnosis, but is not absolutely necessary. I connected the red hose to the manifold gauge set with the open end of the hose, made sure the red valve was closed, then connected the other end to the high side of the compressor.

My blue & red gauges then showed there was some pressure in the system – this reading is pretty meaningless, and will not tell you if it is low on refrigerant. As long as there is some refrigerant in liquid state, it will show the same reading regardless of the amount, if it shows zero on both (or a vacuum on the blue one) when the appliance has been off for a while then you either have a blockage somewhere, or the system is total empty, in which case, this is outside the scope of this guide at the moment.

Now, we want to run the compressor to see what the pressures are doing when it is running, but first we need to purge the air out of the hoses that connects the manifold guage set to the appliance to prevent air being sucked in. I did this by simply opening each valve valve for a couple of seconds, but only do this in a ventilated area, as the refrigerant is highly flammable. Once purged, I closed the valves tightly and started the freezer. In my case, the blue gauge very quickly showed a vacuum of 20inhg (20 inches of mercury) on my gauge, and the red gauge showed an increase in pressure – this is a sign of either low refrigerant or a blockage somewhere.

Now two things can cause a blockage, either contaminants in the refrigerant can physically block a pipe (usually the very thin pipe that is between the filter/drier and the evaporator inside the appliance) or contaminants like water in the refrigerant freezing and causing an ice plug somewhere. As the freezer had not been running, I ruled out the ice plug I then powered the freezer off to see if the low side would come out of vacuum – it did so quite quickly, so I ruled out a blockage, as this shows refrigerant is getting around the system (as I understand it, refrigerant can’t go backwards through the compressor, so it must have gone around the system and refilled the low side).

So, I decided to proceed with refilling the system…

Emptying the old refrigerant

As this freezer was using R600a, which is just pure butane, it is OK to release this into the atmosphere, as it is not harmful to the environment, if you are attempting this on a different refrigerant, you may need to reclaim the old refrigerant, rather than just letting it out, as it is an offense to let some types of refrigerant out into the atmosphere, but his is outside the scope of this guide.

As I only had three hoses, I disconnected the red hose (from the freezer end first!) then connected the valve opening end (the end with a pin in it) of the red hose to the second tap of the middle connection on the manifold (which has a Schrader valve) and the other end of the red hose to free air (R600a is flammable, so it needs to vent outside) I connected the yellow hose to the bottom connector of the middle port of the manifold, and the other end to the cylinder valve, with the cylinder valve off (There is a pin that when the valve is turned clockwise, extends into the cylinder to operate a small valve built into the cylinder, so this needs to be all the way inside the valve, not sticking down past the seal inside) and screwed the cylinder valve to the top of the R600a cylinder (otherwise refrigerant will come out here) With the free end of the red hose out the window, I then opened the blue tap to let out the gas that was in the freezer, when it stopped hissing and the gauges showed zero I closed the blue valve, then let a small amount of R600a out of the cylinder (less than a second) to purge the yellow hose of air, then connected the free red hose to the vacuum pump (suction side of a reclaimed freezer compressor in my case).

Then I turned on the vacuum pump and opened the blue valve, and left it sucking for about 30 minutes. With the vacuum pump still running I turned off the blue valve and then disconnected the red hose (it connects to a self-closing Schrader valve on the manifold)

This then left me with all the connected hoses and the freezer pipework under vacuum. I left it like this for about 30 minutes, and it was still showing the same vacuum, so if there is a leak, it isn't a big one! It would have been better to use a full range vacuum gauge, rather than the one on the manifold (which only has a very small range), to get a more accurate idea of any pressure increase, but I didn’t have one.

Charging the system

I then placed the R600a cylinder on the scales, and hung the manifold in a way so the cylinder wasn't wanting to tip over, and the weight of the hose was constant, basically the hose came out of the bottom of the manifold, didn’t touch anything else and went straight to the cylinder valve. This is important to get an accurate reading on the scales.

With the cylinder on the scales upright (so the refrigerant enters the system in vapour, not liquid state), I then opened the valve on the cylinder and zeroed the scales. (Refrigerant was not flowing into the freezer yet, as the valves on the manifold gauge set were closed, so only the yellow hose has some refrigerant in now, which I heard as the valve opened on the cylinder.) I then turned the freezer on, and when I heard the compressor kick in, I opened the blue valve to let the compressor pump the gas into the freezer.

The data plate on the freezer states it takes 54g of R600a, so I watched as the scales slowly climb up - when it got to about 32g, the scales auto-powered off, so I quickly turned the blue valve off, (I also connected the red hose to the red side of the manifold and the other end to the high side of the compressor - this wasn't really necessary, I just wanted to see what the pressure was showing on the high side when the compressor was running, I also warmed the cylinder up a bit, as the rate of flow had been trailing off because the cylinder was getting really cold) I then reset the scales, and carried on.

When I had put 54g in, I shut the blue valve. I then put a bit more in (5g), to allow for some refrigerant in the hoses, and I had read about the suction side should read around 0 when it is full, and as it was still pulling a bit of a vacuum, I put some more in. I am not 100% sure about this part, and figured I could just let some out, plus I suspect it has a very slow leak. Total that left the cylinder was 60g in my case.

I noticed immediately the condenser on the back was now getting hot at the top (and then noticed it was also getting hot around the door seal) the digital thermometer that was in the freezer was also dropping nicely, so I put a couple of partially filled and partially collapsed (to allow for expatiation when it froze) plastic bottles of water in the freezer, which it refused to freeze before and closed the door.

Disconnecting

Now I needed to disconnect the gauges, and as the low side could still be pulling a bit of a vacuum, I powered the freezer off to prevent any air being sucked in as I disconnected it, the blue gauge then started to rise well above zero, and the high side started to fall, which is expected. I then disconnected the blue hose from the freezer (so the Schrader valve closed and refrigerant didn't escape, which would have happened if I disconnected it from the manifold end first, then disconnected the red hose from the freezer (the red hose had a small amount of liquid refrigerant in, which spat out when it was disconnected, I expected that. I replaced the caps on the service valve tightly (they have a seal in them, in case the Schrader valve leaks) and then turned the freezer back on (it took a while for the compressor to start, as there is a delay built into the freezer to stop the compressor being stated and stopped too often, it think it took around 15-20 minutes to kick back into life.

Results

I left the freezer running on the super freeze setting (the manual states to do this when stating from a warm start) and when I went back to check it a few hours later, the thermometer was at -16c and the water bottles were solid – I left it on super freeze and left it for a few more hours, and when I checked it, the thermometer was at -22, so I turned off the super freeze function, and set the thermostat to the “i-care” setting, which seems to translate to around -19C

The next day, it was sitting at -18.5C when I looked in the morning, and -19C later on that day. At the time of writing it has now been on for about 60 hours, and is showing -20C right now. I had bought a temperature data logger (eBay!) for a different application (a fridge/freezer in a tenants flat was freezing things in the fridge, which a replacement thermostat fixed) so I put that in my freezer, and the results are here Media:Refrigeration_Regassing_(R600a)_-_Graph.PNG, which look OK to me (not sure what happened on the morning of the 8th to make the temperature vary like it did though)


End Note

I am not a refrigeration engineer so I may not have done this correctly, but after reading up on it for quite a bit, I think I did a fair job, a proper vac pump would have been ideal, but I figured the system should be pretty clean as it was still under some pressure, and I figured the old freezer compressor I had would do in this case. Ideally the filter/dryer should be replaced, but I don't have any brazing or lokring tools to do this - The Lokring stuff looks really easy to use, but expensive compared to brazing rods and a mapp gas torch. I would also want to purge the lot with nitrogen if I brazed anything on it too, both before and after brazing, as the refrigerant is flammable and I don't have any nitrogen either...

If you use an old compressor as a vac pump like I did, the output tends to spit oil, I found this out when I fired it up on my desk inside, which wasn't the best place to do spray oil everywhere in hindsight (the fact I had moved the compressor 5 minutes before probably increased the amount it spat out too), so to overcome this, I connected a few meters of clear pipe to the output, and scrunched up a tissue and tied it to the end, this seemed to do the trick. The oil sprays up the pipe to start with (I kept almost all of it vertical), but as the other end is then under vacuum, quite quickly the oil just ran back down into the compressor as there isn't any air blowing out the port.

If you have any comments or suggestion as to the final suction pressure, please post to news:\\uk.d-i-y

--Toby... 22:42, 8 April 2013 (BST)

See also