Charging a NORCOLD SCQT 6406 with refrigerant

[Bolander]

Last summer we purchased our 1985 37 ft. Hunter cutter SV Shadow.
It came with a Norcold SCQT-6406 refrigeration unit for the icebox.
I don't know if this was standard equipment on the 85's, but I'm glad to have it.
My problem is I don't know how to recharge it.
To start, the original refrigerant was R-12. R-12 is no longer made and has been replaced with R-134A.
I bought a can of R-134A and a delivery hose and attached it to the suction valve on the copper piping.
I opened the valve for 5 seconds, turned it off and waited 5 minutes to see if the icebox's cold plate got cold. It did not.
I repeated this procedure a number of times but no change. In fact, the can of refrigerant seemed pretty full when I finally gave up.

My current thinking is that I have to purge the system of it's existing refrigerant before I can charge it, but I have no idea how to do that or if that is the right thing to do.
Attached are photos of the unit and it's valves.

Any advise will be appreciated. TIA

 

[smokey73]

Not sure I undersand what you did here.

Did you use the fittings that were already installed or put some kind of conversion fitting to put in the R-134? It is my experience that the charge connection fittings for R-12 are different than the fittings for R-134. Are you sure the PO didn't do a conversion from R-12 to R-134 sometime in the past?

I don't think you can mix R-134 with R-12. Secondly, if you purge the system make sure you don't tell anyone, even us and certainly don't brag about how you purged the system. It is a violation subject to significant fines if you purge systems without the mandated recovery systems to capture the R-12 and not release it to the atmosphere.

 

[DougM]

R12 and R134 are not at all compatible. By the time you legally purge the R12 and recharge with R134, then get the compressor to run, it might be cheaper to buy a new fridge.

 

[SEMPERAVANTI41]

80 percent of a/c or refrigeration problems are electrical. Before doing anything mechanical, all possible electrical faults should be eliminated.
What makes you think the system need a recharge? Without knowing that the system is low on freon, just adding more is not the answer. From your pictures it appears that there is a sight glass. When you turn on the system, does the compressor turn on? You should be able to feel it move when turned on and hear it hum if it's working. If it is working, do you see bubbles in the sight glass? Bubbles will indicate a possible loss of freon, an inexpensive gauge set would be be better still.

I bet the cheapest fix is either going to be a new refrigerator or possibly a retrofit kit something like an Isotherm Compact "2010-ISEC

 

[DeniseO30]

NEVER Assume it needs Refrigerant. R12 and R134A are NOT compatible because of the oil in the compressor. You could ever really remove the mineral oil and use PAG.

12/24 volt refrigeration was "new" in the early 80s if memory serves...

Please! Don't mess with it! Until you do this at least:
Start the system... listen for gurgling at the evaporator... let it run, if you do hear it running. let run a good hour or so. The Evap should slowly get cold, colder, very cold. The lines should not get frost.. the "frost line" should stop just a inch or two from the evap. Compressors get warm to hot. (normal)

The system was worked on by someone. The sight glass is really not needed. It's old school for large systems. The ports are called schrader valves. (like car tires but not the same thread.)

The reason people should not mess with miniature refrigeration is the the critical refrigerant charge. Just connecting a 3ft gauge hose will cause a loss of 3 oz or more. The only proper way is to weigh the charge in with an electronic scale that reads digital.

 

[jeepbluetj]

<snip>
The reason people should not mess with miniature refrigeration is the the critical refrigerant charge. Just connecting a 3ft gauge hose will cause a loss of 3 oz or more. The only proper way is to weigh the charge in with an electronic scale that reads digital.

Or if you really want to go old school, a heated dial-a-charge. (Guess how I payed my way through school)

But to the O.P. saving a 20+ year old (maybe 30+) refrigerator is folly unless you're a tech and if you were the question wouldn't be asked.

1. It may just not work (compressor doesn't compress, leak in a line, leak in the evap or condenser, whatever passed for electronics is toast, etc...)
2. If it does need a recharge and it was R12, you need to convert to 134. There are compressor oil compatibility issues. You need a decent vacuum pump and a way to measure the recharge. Oh, and venting refrigerant as mentioned above is indeed rather illegal.
3. If you get it running, it's still awfully old and likely to break again.

Just replace it all. If you're really on a budget a dorm fridge will run off of a small inverter reasonably efficiently. An engel (or knock off) will be more efficient. Likely could find a direct replacement with a typical dometic/norcold/frigiboat/isotherm conversion. Definitely would be more efficient in terms of power use.

HVAC/fridge guy storytime: Can't tell y'all how many times I'd show up to a A/C call and the homeowner would say "I think it just needs some more freezone!." Drove me nuts. #1 failure was condenser fan/compressor capacitor. I never did add "Freezone" although I went through lots of R-12 and R-22. Never wrecked the van, so I've had that going for me.

 

[DeniseO30]

I gave away a dial a charge they were pretty accurate but I'm retired I got rid of everything my son passed at 35 so he didn't take over the business..
OP, JUST LET IT RUN FOR AN HOUR, SEE IF IT STARTS TO COOL IT WILL NOT START COOLING IN 5 MINUTES! The refrigerant if there's any left will be mixed with the oil and in the compressor and it takes a while for things to separate and start moving through the system that's been sitting for who knows how long. You may be able to find somebody with a little bit of R12 if you're lucky.

 

[Bolander]

Not sure I undersand what you did here.

Did you use the fittings that were already installed or put some kind of conversion fitting to put in the R-134? It is my experience that the charge connection fittings for R-12 are different than the fittings for R-134. Are you sure the PO didn't do a conversion from R-12 to R-134 sometime in the past?

I don't think you can mix R-134 with R-12. Secondly, if you purge the system make sure you don't tell anyone, even us and certainly don't brag about how you purged the system. It is a violation subject to significant fines if you purge systems without the mandated recovery systems to capture the R-12 and not release it to the atmosphere.

Thanks for your response. I didn't add any valves, it came like that and the R-134a hose connection hooked up to the suction pipe and not the delivery pipe.
I would never discharge the R-12 in the atmosphere.
It makes sense that R-12 wouldn't mix with R-134a, yet the connection hose did fit for the 134a.

R-12 apparently is highly coveted and demands exorbitant prices.
So maybe you're right.

 

[Bolander]

R12 and R134 are not at all compatible. By the time you legally purge the R12 and recharge with R134, then get the compressor to run, it might be cheaper to buy a new fridge.

I think you are right, I'm leaning toward a total replacement

 

[Bolander]

I gave away a dial a charge they were pretty accurate but I'm retired I got rid of everything my son passed at 35 so he didn't take over the business..
OP, JUST LET IT RUN FOR AN HOUR, SEE IF IT STARTS TO COOL IT WILL NOT START COOLING IN 5 MINUTES! The refrigerant if there's any left will be mixed with the oil and in the compressor and it takes a while for things to separate and start moving through the system that's been sitting for who knows how long. You may be able to find somebody with a little bit of R12 if you're lucky.

Yeah, that seems like the most reasonable thing to do, just let it run for an hour. If It doesn't get colder I'll probably pull it and replace. THX

 

[smokey73]

I actually have a 30 lb cannister of Pure virgin R-12 with about 24 lbs left it that I purchased many years ago.

If your fittings accepted the R-134 fittings without any modification then I think its probably a sure bet that the PO converted from R-12 to R134a at some point. How good a job he/she did may be part of the problem with how your system is performing. If he didn't purge and evacuate the system then draw a vacuum on it for an extended period of time allowing any moisture to evaporate and then use some sort of purge product to remove the oil compatable with the R-12 before he charged it with new R134a and its compatable oil it will never work right. Even then, R-134a is not as efficient as R-12 in cooling (some will dispute this but IMHO it is just not a good.) Add to that it is my understanding that R-134a leaks easier from the hoses if they are flexible. You may be way ahead in going to a newer replacement unit like an ISOTHERM. I have one and I am very happy with it.

 

[Bolander]

80 percent of a/c or refrigeration problems are electrical. Before doing anything mechanical, all possible electrical faults should be eliminated.
What makes you think the system need a recharge? Without knowing that the system is low on freon, just adding more is not the answer. From your pictures it appears that there is a sight glass. When you turn on the system, does the compressor turn on? You should be able to feel it move when turned on and hear it hum if it's working. If it is working, do you see bubbles in the sight glass? Bubbles will indicate a possible loss of freon, an inexpensive gauge set would be be better still.

I bet the cheapest fix is either going to be a new refrigerator or possibly a retrofit kit something like an Isotherm Compact "2010-ISEC

It does run and there is a sight glass. I'll check it for bubbles. I'm leaning toward replacement. Thanks. I'll post the final resolution. As for now, it's back to the igloo cooler and ice.

 

[Bolander]

I actually have a 30 lb cannister of Pure virgin R-12 with about 24 lbs left it that I purchased many years ago.

If your fittings accepted the R-134 fittings without any modification then I think its probably a sure bet that the PO converted from R-12 to R134a at some point. How good a job he/she did may be part of the problem with how your system is performing. If he didn't purge and evacuate the system then draw a vacuum on it for an extended period of time allowing any moisture to evaporate and then use some sort of purge product to remove the oil compatable with the R-12 before he charged it with new R134a and its compatable oil it will never work right. Even then, R-134a is not as efficient as R-12 in cooling (some will dispute this but IMHO it is just not a good.) Add to that it is my understanding that R-134a leaks easier from the hoses if they are flexible. You may be way ahead in going to a newer replacement unit like an ISOTHERM. I have one and I am very happy with it.

I'll look into the Isotherm.
You should look into selling that canister of R-12.
Check out ebay, I think you could make some serious money.

 

[Bolander]

Or if you really want to go old school, a heated dial-a-charge. (Guess how I payed my way through school)

But to the O.P. saving a 20+ year old (maybe 30+) refrigerator is folly unless you're a tech and if you were the question wouldn't be asked.

1. It may just not work (compressor doesn't compress, leak in a line, leak in the evap or condenser, whatever passed for electronics is toast, etc...)
2. If it does need a recharge and it was R12, you need to convert to 134. There are compressor oil compatibility issues. You need a decent vacuum pump and a way to measure the recharge. Oh, and venting refrigerant as mentioned above is indeed rather illegal.
3. If you get it running, it's still awfully old and likely to break again.

Just replace it all. If you're really on a budget a dorm fridge will run off of a small inverter reasonably efficiently. An engel (or knock off) will be more efficient. Likely could find a direct replacement with a typical dometic/norcold/frigiboat/isotherm conversion. Definitely would be more efficient in terms of power use.

HVAC/fridge guy storytime: Can't tell y'all how many times I'd show up to a A/C call and the homeowner would say "I think it just needs some more freezone!." Drove me nuts. #1 failure was condenser fan/compressor capacitor. I never did add "Freezone" although I went through lots of R-12 and R-22. Never wrecked the van, so I've had that going for me.

I enjoyed your post. You have good advice. THX

 

[DeniseO30]

Oh you're very welcome I try to help it's not always what people want to read but when it comes to older refrigeration units use and throw away is the basic concept for everything even though for boats, it's even more expensive! I have a vintage a Alder Barber cold machine in my boat, I'm not going to fix it if it goes down, I'm just going to replace it with a Norcold I love that "swing compressor" they use.

I realized over the years, It's really hard to train air conditioning people how to repair service install refrigeration.

 

[Leeward Rail]

Glad to see.people who understand AC. I can't count how many people want to refill their vehicles with propane or some other crap because they don't see why it should be repaired correctly. Recovery ? Vacuum ? Nitrogen ? Digital scales ? PAG oil ? Dye ? UV ?

Yup.. It's not brain surgery but you need the right gear and the knowledge to do it right. Otherwise it won't run well, last long, and leak Freon into the air. None of those are a good thing.

Unlike a vehicle, switching to a newer, more efficient unit for a boat makes more sense than fixing a decades old system

 

[DeniseO30]

Bolander did it start chilling after running it an hour or more? or you going to replace it? Just wonnering

 

[dLj]

Bolander did it start chilling after running it an hour or more? or you going to replace it? Just wondering

@Bolander Also curious - I don't have this problem.... yet.... (knock on wood)...

dj