Northland NM11B R-134a level?

[LKB]

Greetings:

I have a 13 year old Northland NM11B. A couple of years ago, it started being unable to cool below 45F. I have an excellent HVAC technician available (Jay Shook), and he quickly figured out it was just low on R-134a, so he cut the fill tube and sweated on a service port, added some R-134a, and all was well.

A couple of weeks ago, it happened again, and Jay was able to resuscitate it quickly by just adding some R-134a.

Well, it’s happened again, and unfortunately as temps are hitting 100F Jay is slammed with emergency AC repairs and likely will be for some time. I’ve added R-134a to automotive AC systems before, and so I’d like to just figure out how to top it off to keep it running until Jay can get out to give it a closer look.

The service plate says the design pressures are 101 PSI (low side), 218 PSI (high side), and system takes 7 oz. of R-134a.

So, stupid question: what PSI should I fill to (obviously, adding it very slowly while the compressor is running)?

Thanks — LKB
Austin, Tx

 

[Fitter30]

Guess this is a piece of refrigeration. Quick search its obsolete. A 30° coil 26 lbs suction give you 40° .
Pressures listed on name tag are not running pressure there test pressures what the coils to handle. The system is a critical charge unit 7 oz has to be weighed in after unit is in a vacuum for proper operation. Unit probably has a leak which can be very hard to find with a system holding so little. 2 ozs could stop the unit from cooling. Were what temp are trying to get?

 

[Sponsor]

 

[LKB]

Guess this is a piece of refrigeration. Quick search its obsolete. A 30° coil 26 lbs suction give you 40° .
Pressures listed on name tag are not running pressure there test pressures what the coils to handle. The system is a critical charge unit 7 oz has to be weighed in after unit is in a vacuum for proper operation. Unit probably has a leak which can be very hard to find with a system holding so little. 2 ozs could stop the unit from cooling. Were what temp are trying to get?

Yup, it's a SubZero style large refrigerator / freezer, with "replaceable" refrigeration modules (NM11B) mounted on top (one for the freezer, a one for the fridge). Was wanting the fridge unit to hold temps in the low 30's, which it has done for years.

And yes, Northland has indeed now discontinued it, so keeping it running it is going to take a tech who is willing and able to McGuyver the refrigeration modules (which my tech indicates are pretty straightforward and serviceable if you know what you are doing).

Fortunately for me, my superstar HVAC tech happened to be in the area today and dropped by early. He hooked up his equipment and injected a tiny bit of E-134a, and it's now holding steady at 33F. He indicated he might have underfilled it slightly last time he was out, because as you indicate there's such a tiny amount of coolant that it's very hard to measure, and with the recent return of the Texas summer heat the ambient indoor temp is now a few degrees higher than it was before.

He also warned me off of trying to DIY this, as he says you need the very pricey professional digital equipment to get it right, and it would be very easy to overfill the system and cause it to completely fail with the inexpensive automotive gauges.

 

[LKB]

a tiny bit of E-134a

Obviously, I meant R-134a.

 

[Fitter30]

Glad he got it going

 

[LKB]

Glad he got it going

Well, about 2 weeks later, it happened again, so obviously I had a leak.

On Jay’s advice, I contacted the manufacturer (Marvel Refrigeration — they have discontinued the Northland line but still have parts) and ordered a replacement evaporator ($350; the tech I spoke with strongly suggested I also get the replacement heat exchanger/capillary tube kit ($65), which I did).

Jay was out here yesterday, and for an experienced AC/refrigeration tech with the right tools it was pretty straightforward — pull the module, remove the evaporator / heat exchanger / capillary tube, weld/solder the new pieces in place, pressure & vacuum test it (mine had a pinhole leak at one new joint that required a touchup; after that it held vacuum at <600 microns), add 7 oz. of R-134a, reinstall). Took about 2 hours; works like new, and while the module was out it gave me a chance to give it and the enclosed area atop the fridge a thorough cleaning / de-dusting.

In looking at the old parts, I’m 99% sure the leak was somewhere along the old capillary tube, but as Jay indicated it was probably a good idea to replace the evaporator while we had it torn down.

Moral of the story is that if you have one of these units, before you spend $3500 (plus shipping) on a new NM11B module, if the compressor is still good and the leak isn’t on the condenser, a good tech can probably repair it for a quarter of that price.