Cap tube or txv system ?

 

Cap tube. Every fridge i deal with is cap tube (residential)

 

You would need to know what those numbers should be.

 

Sub cooling is not always high with a restriction unless it's overcharged to compensate. With correct charge SC is usually normal.

 

True, it would depend on where the restriction is. Typically in cap tube systems thou I find that restriction in the tube itself or the filter. So absent of a receiver a correctly charged system can only put that refrigerant in one place.

 

Truth be told I never check for either. Once I gauge up after the system has been off, I look at the standing pressure. Low charge will show low static. Once turned on I look for a drop in back pressure compared to normal. Then when system is turned off I look at the equalization rate.
On domestic refrigerators it would be quicker to pull and weight back in the correct charge amount. Then go from there.

 

Let's assume your fridge at home is our 134A or R12 (only two refrigerants I've ever seen in a residential fridge). If you have a suction access port, instal your gauges while it's running, turn compressor off and watch how quickly the two pressures equalize. If they equalize in the normal amount of time, then it's shortof gas. Easy peezee. If you still are in question, recover the charge and weigh in the proper amount it's the only way to properly determine your situation or just throw the freaking thing in the garbage and buy a new one.


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No subcooling usually means low charge. The charge is so small on those, if you suspect low charge just add a little and see what happens. I usually do that on small reach ins even if I'm pretty sure it's a restriction. Less than a pound of 134A or 404A is a lot cheaper than a misdiagnoses.

 

Where the restriction is suspected should be a temperature drop ; since the restriction would cause flashing of the liquid refrigerant . This is where a laser temp sensor is valuable .

 

Let me paint a better picture for you guys and i want you all to tell me what would you do because im still new. And this happens to me daily thats why im asking. Ok i get to customers home, its a collect call meaning they dont have a warranty he/says my fridge isnt cooling. My company's process is to diagnose then give the customer an estimate. Ok you with me so far? This happened yesterday btw. I amped the compressor it was pulling low amps and hot, I looked at the evap and it had partial frost pattern. Keep in mind a fridge doesnt come with any access ports at all. I now have to give a duagnosis before i can throw on a saddle valve. I definitely cant throw on a line tap because i cant leave it on i would have to recover and braze shrader valve on. I now have to determine restriction or low charge and give a correct price. How can I make this easier on myself?

 

You can't. All you can do is tell them that they either have a refrigerant leak; which means finding and repairing the leak, evacuating, and charging with new refrigerant. Or, they have a restriction; which means replacing the cap tube and filter, evacuating, and charging with new refrigerant.

Both procedures are time consuming and probably similar in cost. However, finding and repairing a leak is not guaranteed as some tubes are not accessible in a residential refrigerator.

When we have run into this, we tell the customer to start shopping for a new one. We also offer to try to add gas to the system to possibly buy them some time in finding a replacement.

For what it's worth, 99% of the ones I've seen like you describe above are low on charge. I can't remember the last restriction I've seen in a residential fridge.

 

People still fix residential fridges with refrigerant issues???

 

The new samsung family hub fridge cost about $3400. Would you not try to repair it?

 

Now to answer the question. Commercial prep tables are the same principle. My procedure is if I suspect a refrigerant issue I pull vacuum and recharge to nameplate. If the suction is too low after charging, I quote converting the unit to TXV. You can get a feel for it overtime without recharging, but often I can have the unit recharged just as fast as checking SH and SC etc. Also, my method is easy to teach my new guys.

 

Ive learned the hard way , do NOT repair domestic refridges if they have refrigerant problems. They will not last very long after the repair.

A lot of them have start component issues , and those are easy peasy , or defrost heaters , or evap fan

Leakers , tell them buy a new fridge and walk away , even if it cost 3400

PS ... for 3400 you would have thought the engineers would have have done a much better job , but its the same crap used in the cheap lines

 

The huge problem with the solution "just check subcooling" is that by the time you even HOOK UP a high side hose to a domestic refrigerator holding 4oz of R134a, you're low on charge. Sure a stubby with low loss fitting might only lose 0.5 oz but it's still going to affect it.

That's why, I still preach what I have for years now. Pull the charge, pull a quick vacuum, weigh in virgin charge. If it starts cooling then it was low on charge. If it doesn't, it has a restriction.

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All of your replies have helped me greatly and gave me a better scope on what i am dealing with. Im seeing there is no magic trick to tell yhe difference without tapping into it. I see the solution will be to explain to the customer it can be one of the two and give them a ballpark figure of each one and go from there. Thanks guys i really appreciate it. I have a long way to go diagnosing these units.

 

Just had one this afternoon. 12 year old residential Refrigerator, too warm. Discharge line hot. Suction line cool. Fans running. No frost. What the heck? Put on a piercing valve and system running in major vacuum. Add refrigerant and pressures come up. System is cooling again. I told the homeowner that she has between 12 hours and 12 years for it to leak out again. Trying to find and repair a leak on one of these is not very probable.

 

Just had this one this evening

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It's on a cold tech freezer 2 door. What's crazy about this restriction is that I still have a suction pressure. Normally restrictions I see have the unit running in a vacuum. R404a for the curious. Going back in the morning to change.


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Is the suction pressure 35 lbs?

PHM
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Reason this all happened was the condenser fan motor went out. No pressure switches on these units so it pumped up to no telling how much head pressure. I'm assuming it blew stuff through the drier and right into the cap tube. Funny it made it all the way to the end before it restricted its self.


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Low charge could look the same.

 

Factory weight charge.


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Good luck. 3 times now on that brand unit, I changed cap tube to no effect. Ended up discovering desiccant from drier had broke loose and clogged the 3/16" liquid feeder line that goes from drier up to evaporator. I even disconnected suction and was blowing desiccant beads out of evaporator coil and suction line. Suction copper is SOOOOOO thin that the slightest bend of service loop INSTANTLY kinks the line. Twice now my solution was to run new liquid line, new suction line, and convert to TXV. On one of them the CPR valve was also leaking, so I just replaced with an MOP txv and eliminated CPR altogether. Good luck

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If the CPR is open all the way, it's as if it isn't there. It can't increase the pressure on the compressor. If you opened it and got 50# suction, then the restriction is not the cap tube. Maybe the CPR is the restriction.

 

Brand new CPR


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I'm not getting how you can suspect a restriction with a 50 psi suction? What did comp amps do at that SP? If low, possible bad discharge valve after loss of condenser fan? Also, new parts can be 'bad'.

 

From your experience what's the symptoms of a bad discharge valve? And how would you check if you couldn't pump he unit down


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Temporarily disconnect your condenser fan and watch the high side pressure.

 

Think compression ratio.

 

I had a compressor earlier this week with a missing discharge valve, only one out of six cylinders. The compressor was drawing rated amps, but was shutting off on the motor protector.

 

This is a cold tech unit yes?

I have successfully converted 2 of these units to TXVs now.
I have found their condensers are usually generously sized.
Put the valve in...no problem. Worked perfectly

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Yeah cold tech. Unit seems to be working fine after cap tube replacement. Although the only tube I could find was close to 1 foot short. I watched it pull down. I told the owners what we are dealing with. Can't get OEM parts if the company is out of business. Unit seems to be working great.


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