View Full Version : Change from 12 to 22 ?
Poodle Head Mikey
05-17-2004, 03:28 PM
This is a very basic walk-in box - 1 1/2 HP TPCo tin can originally on R-12 - now using R-414B. It has a bad compressor at the moment. The customer has a row of A/C units sitting along with this one high-temp refrigeration condensing unit.
My original thought was to change to an R-22 valve and install an R-22 compressor as the replacement.
My question is: will the original R-12 condenser coil be sufficient to reject the heat properly while using R-22?
05-17-2004, 05:14 PM
I've done this many times. If you select the new R22 compressor to closely match the capacity of the old R12 pump, the total heat of rejection (THR) will be the same and the condenser won't know the difference. There is a factor of less than 5% +/- for the heat transfer characteristic differences between the two refrigerants, but you wouldn't be able to easily measure it in the field.
A couple of things to watch for. The original was a Tecumseh 1.5 HP unit? It was probably rated as a medium temp unit and therefore would have a condenser sized for +25 Deg F SST max, so if this is on a walk-in cooler you'll be running right at the upper limits and will get 125-130 Deg F condensing temps with 90 Deg F air into the nice clean condenser coil. :D
Also, check your dual pressure switch. The R12 units were typically fitted with R12 range controls (not an All-Range) and the HP tops out at 250#, so you'll need a new control as well.
If you pick a CR Copeland, a new Sporlan TXV and drier, you'' be good to go.
05-17-2004, 10:53 PM
And yuou'll wana remember that wine gets better with age, as do women. Condensors however ... DO NOT!
Make certain your air cooled condensor is in primo shape before committing to this project.
I like what Ice said. I would maybe lean towards going with a complete new condensing unit though. It is easier on the install part.
One electrical connection, one weld and one flare fitting.
All the controls are done and set for the system.
New fan, new condensor. New can for controls to mount up to.
No fiddling around.
If you bid the job, you'll be in and outa there is no time at all by going with a brand spankin' new unit, over just a new compressor and pressure switch.
jus my two cents worth.
05-17-2004, 10:57 PM
I'd go with an entire unit, also.
If it's not an outdoor unit, it'd only be a few bucks more. Cheap insurance.
An outdoor unit, well, that might be a big difference, but you'd definitely want to check out the capacity of the condenser before using it with 22. I've done it, but it was a tad warm...:eek:
Poodle Head Mikey
05-17-2004, 11:14 PM
Well, it's a real regular customer - I can do whatever I want without being questioned. Always pays the bill - never complains - always thanks me for comeing out. But I do try to be very fair with the guy too.
This particular condensing unit was replaced about five years ago - shorted compressor. Two years ago the compressor was replaced - shorted compressor. Now the compressor ohms OK but the breaker trips as soon as the compressor wires are attached. Megs to ground OK too. Why does the breaker trip? I have no idea, but with everything wired in Except the compressor terminals - the breaker stays in. New breaker too. <g>
The box has plenty of capacity. The second 1 1/2 HP unit on this box is primarily a back-up although it also tops off the load when it's 90+ outside.
I was just thinking that maybe it was 'time' to switch refrigerants. I like R-22, it's cheap, they use it in all the A/C equipment anyway, and it will be around longer than this unit will.
Maybe I should stop thinking so much? <g> Just leave the R-414 and replace the compressor like for like?
05-17-2004, 11:29 PM
What's up with these units shorting to ground?
If this latest unit is not showing a ground short with your meggar, but IS tripping the breaker ... one or the other is not right.
Either your meggar is outa whack or the circuit breaker is faulty.
Check your wiring, one mo time ...... If you have an ANNIE, use it before condeming the unit.
05-18-2004, 06:18 AM
Use your amp probe, and check for a locked rotor.
Poodle Head Mikey
05-18-2004, 08:43 AM
I have the same one myself. (What's up with these units shorting to ground?)
But I just don't know. The unit that routinely goes bad is the primary unit - it runs much more than the back-up unit. But if it's a power quality issue why is it only this one compressor? Although this unit has had a fan motor replaced too.
Sorry - do not have an Annie. Didn't buy one 30 years ago (I used to so almost entirely industrial work) and still don't have one. Which seems especially silly in that just the other day I realized that I have at Least four H-10 leak detectors! <g>
You: "If this latest unit is not showing a ground short with your meggar, but IS tripping the breaker ... one or the other is not right. Either your meggar is outa whack or the circuit breaker is faulty."
I thought the same thing. I first checked with a Fluke set to meg-ohms, and then with a regular megger - no short to ground. So I replaced the breaker. Still tripped. So I pulled the wires off the compressor terminals and all is well.
No time to check for LRA - the trip is instant.
It sure had me looking over my shoulder for Allen Funk and his camera - I can tell you that. <g>
I know the wiring is right - checked it wire for wire and I have a running duplicate unit sitting 5' away for comparison.
Leave the compressor in the circuit - the breaker trips.
Take the compressor out of the circuit - the breaker stays.
Poodle Head Mikey
05-18-2004, 03:40 PM
This morning I had to locate a Copeland CRD1-0200-PFV compressor for a Hussman combo rooftop. For some reason I had thought that line of compressors to A/C units. But I looked it up and found Copeland curves the capacity from -10 to +55 on R-22.
AND, that at a 30 degree F. suction it pumps 14,400 BTU's. Which contrasts nicely with the TPCo ARHB7511 R-12 compressor that I started off wanting to replace. The R-12 compressor curves to 14,250 BYU's at 30 degrees F.
I have a hard time believing that the extra 250 BTU's will cause a problem with the THR at the condenser.
05-18-2004, 06:30 PM
Since all the manufacturers lie equally about their ratings, to match them up like this is quite safe. ;)
You should end up at roughly the same condensing temperature as it was with R12 (which as I said will be high since you're at the upper end of the operating envelope of a medium temp unit).
While I understand and really do agree with some of the others here that we should be replacing the entire condensing unit in a case like this, I find as you probably do that there are a lot of customers out there if given the choice will opt for the least cost repair job every time. I don't mind because I'll make money either way......and usually more by continually replacing components rather than units. :D
As for the shorted compressors........it may be too late now but check the LP switch and see if it's stuck closed. I've found a lot of dead pumps bought the farm due to running into a vacuum during defrost and off cycles for a year or two and nobody noticed.
05-19-2004, 12:56 AM
The Protoair claims another compressor.:rolleyes:
05-19-2004, 03:18 AM
05-19-2004, 03:50 AM
Unless it's three phase :)
if you convert, or replace, add a phase monitor, only about 30 bucks and cheap insurance.
Change the button at the inlet to the evaporator or you may have some superheat issues.
If the customer is as good as you say I too would pitch it to him to replace the skid.
I was just called in on a condenser that was installed in November, new Compressor in December and they couldn't get the other company to come back out. They sized it 2/3 over capacity of the evaps and it was 1/3 more than they needed for the box, I ended up selling them new evaps and condenser. Something is wrong if your having multiple failures, even they are a few years apart, find what's killing them. If the customer knows you know what your talking about, sell them on the best repair.
05-19-2004, 05:11 PM
I agree that the distributor nozzle requirement is different for R22, I've changed out a ton of old R12 C-Store systems over the years from 12 to 22 and have not had any problems with performance or compressor longevity using the original nozzles.
05-19-2004, 06:03 PM
That's why I said may have a problem, as I understand they are more critical on smaller evaporators, I too have changed out TXV's and left the old ones in without problems but most have been 12k or larger evaps
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