Been doing residential work for some time. Been doing refrigeration for some time as well...just don't get as many calls for it. But I do get by. Just sometimes get myself a bit confused...
A lot of my refrigeration calls on walk in freezers and coolers are frozen/heavily frosted evap coils. Sometimes adjusting the TXV (out) will stop the coil from freezing up but usually the valve just needs to be replaced.
I guess what I can't wrap my dumb head around is what about the TXV operation causes it to make the coil freeze?
Where is so much info to cover with this question I don't know where to start.
Are your systems defrosting properly?
Are the t-stats adjust correctly?
Door gaskets good?
Are the boxs in good shape?
Are the condesing units operating properly?
Is the evaporator fouled causing the coil to ice up.
There are alot of things to take into consideration before adjusting the
In my experince usually you found your superheat is out range.
Or the TXV is bad and needs to be replaced
Waddya mean don't thaw out the frig with a knive?
Are you taking superheat reading while adjusting the valve? Arbitrarily adjusting it is not a solution.
Freezups are usually caused by too much moisture or a defrost problem. A TXV that is starving the evaporator could cause a freezeup, but thats rare. I think your looking in the wrong place for the cause of the problem.
My biggest causes I come across on freeze-up calls like this is kitchen staff not closing the door/door closures not working properly then the other is those silly stocker guys packing stuff up around the evaporator and blocking airflow. One other thing is to check and make sure your cold control cycles the box off at the proper temperature, stats can be off from what your "setpoint" you see. Operation must be checked with a thermometer you trust.
That concern applies mostly to W/I coolers, of course. I've found those W/I temp controls (Honeywell or the other guys...can't remember right now) come brand new, out of the box, with the differential set to MINIMUM. Wrong answer.
Originally Posted by ryan1088
If somebody replaced the control, set it to desired temp, got a signature and walked out, he's asking for a callback.
That won't do. The differential needs to be established. The cooler needs adequate OFF time to defrost - especially IF the system is prone to frosting up while cooling. I shoot for 6-7 degree differential with hopes of getting 33# cut out and 39# cut in box temp.
As for W/I freezers iced up. Here recently I decided that, if the clock is working, elements are working, and all seemed good on my system run through, I'd be doing a DIS-service to NOT replace the termination tstat/fan delay. Too many times they worked when I visited, only to find it did so for me only. Now being an intemittent issue, REPLACE it as the likely suspect AND the cheaper alternative if I was wrong.
Excessive FROST in a WIF,on the other hand, and I start being concerned about opened doors or some source of moisture. USUALLY (but unfortunately not always) ICE formed by frost being there too long leaves the DEFROST cycle as suspect. HOWEVER, a cooling cycle misalignment (like a bad fan motor or some other out-of-balance factor) can still be the cause of ICE.
FROST is new stuff. ICE is old stuff.
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The TXV is the most frequently WRONGLY replacecd component in the refrigeration industry and has been for a very longggggggggggggggggggggggggg time.
IF the application is sized correctly, the condenser and evaporator coils are clean, THE PRESSURE CONTROL OR T/STAT is set correctly and the superheat and sub cooling is correct there is something you are missing. High humidity loads, bad gaskets, doors left open, etc.
99 out of 100 times when an expansion valve fails it wil fail CLOSED. In many decades I have never seen a FAULTY expansion valve cause a coil to freeze. Improper distribution of refrigeration or low charge may cause part of the coil to freeze (usually lower portion of coil).
Good luck in your search for the problem.
If you really know how it works, you have an execellent chance of fixin' er up!
Tomorrow is promised to no one...
so your saying a faulty TXV will never freeze the coil
Originally Posted by rayr
doesn't a faulty TXV fall into the improper distribution description that you gave
and if so, are you not contridicting yourself
You have never seen a faulty TXV freeze a coil before? I agree that they are often replaced for the wrong reasons , but I have also seen a faulty valve starve an evap.
Originally Posted by rayr
If you've actually ruled out all the other more likely scenarios listed by the guys before me, then the TXV can actually cause freeze-ups. This happens when the coil is operating in a 'starved' condition, just like I'm sure you've seen in the A/C's you service.
Originally Posted by sandpipertech
But as stated by the other fellas, suspecting the TXV oughta be your last stop, not your first.
Last edited by engineerdave; 06-10-2010 at 02:19 PM.
The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.
Check the box, make sure that it wasnt bumped with an electric pallet jack giving you a gap in the insulation wall. If you can bump it back and if you cant bump it back from the outside, or repair it somehow, cover the slot with clear tape, and foam it in.
Haha, you guys are great. Thanks for all the posts!
My question was very... VERY general, I know. And for that I apologize. I wasn't referring to any job I was on in particular. But I know the last walk-in freezer I was on had a coil that kept frosting up very badly. NOT Ice, just very heavy, thick frost.
I backed the TXV out 1 full turn. Never saw frost on it again. However, the box also never reached set temp. I replaced the valve, did not make any adjustments, went back 2 days later and it was holding at -10.
I never checked superheat on this first call when I adjusted the old valve because, like I said before...a bad TXV is a bad TXV in my opinion and very rarely have I been able to get a TXV to start working properly again by adjusting the stem.
I think adjustments should be made on startup under very certain circumstances. I do agree that superheat should be checked on startup...I guess I've just been lucky enough to have a new valve produce the proper amount of superheat every time.
I know what the books say about all this. But when I walk out of the office everyday...I step into the real world and so I must adapt...and overcome!
Also, I always check EVERYTHING else before looking at the TXV. Anything from making sure the defrost timer is advancing and the heaters amp out ok to checking the seals on the door...
If moving the stem make the problem go away then you have junk floating around in the system. Drier needs to be replaced. Most refrigeration evaps have a pressure port(s). Its not that hard to get a superheat reading and end all of the speculation and guessing.
It's a rare that I find a bad txv and they do crash but more often it's just a bad or weak power head.I do agree(know) that a starving evap due to a txv not feeding right will cause the evap to ice up.