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low suction,low head,frostback

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8.8K views 25 replies 13 participants last post by  kj1  
#1 · (Edited)
Hi All, Just found this site and thought I'd throw my latest at ya. I got called to a manufactured home and found a 5ton split(straight cool)bad compressor. I don't know who designs these things but the installation is a piece of work! The air handler is located in the utility room off the kitchen on one end of the house with the return just outside the kitchen door,so the only place it draws air from is right there and to top it off theres a supply duct blowing right around the corner.My plan is to run the return more to the center of the home shortly.(tricky all the ceilings are vaulted).Anyway,replaced the compressor and start components,multiple evacs,cleaned coils(both) and installed both suction and liuid filters, and charged her up. I am getting frostback all the way to compressor,suction press won,t come up much more than 45-50 lbs no matter how I adjust the charge(it's overcharged now according to the nameplate. Checked orifice size, and its proper for 5ton (93),fan speed is good,no restrictions in liquid line. Head is low also,and amp draw is below normal. I'm guessing the unit had icing issues before it went bad too. My initial diagnosis was lack of air or load,now I'm baffled.Larger orifice maybe? Too much 22 it frosts,too little same.Any ideas?????
 
#2 ·
"kj1 is on a distinguished road". Who's running this joint?

Oh, almost forgot. No step by step instructions allowed in this forum. Sorry.
If you're a real tech, then apply for professional membership. Totally free. Then post in the technical forum.
 
#3 ·
you don't sound like a d.i.y.'er (not for me to decide however). so just get your post count up real quick, submit your credentials and go to the pro's forum for answers to questions such as these after the membership committee approves you. it took me a day or two after applying to be accepted. you can get your post count up real quick by going to the hall of shame, looking at some of the f***'ed up installs and then posting your comments to the thread. (a tip another pro recommended to me when i joined) regarding the problem your having, i think i can say without overstepping my boundries that i would make sure my compressor was correct, weigh in my charge, make sure coils are clean and airflow is good. it seems a identical swap on the compressor with all other parts being the same wouldn't require an orfice change. it'd need to be clean and flowing and your gauge readings seem to show it is. don't redesign anything til you can make it work like it did prior to compressor failure. i'll get flack from the moderaters if i go any further. good luck and hopefully welcome to the site. it's one of the best tools i have.
 
#4 ·
Yep, that disclaimer of yours about flack should make the step by step instructions that you provided seem like something other than step by step instructions. Maybe it'll slide right by the mods. Of course they don't seem to be paying attention anyway. The guy has ONE post and they seem to favor him over at least a hundred regulars who've proved that they know their stuff. He started out on a distinguished road. Geez, why don't they drop that crap already!
 
#5 ·
step-by-step instructions assist someone who doesn't know how to perform a specific procedure get walked thru the procedure, with the general intention being that afterward they will then know how to do something they previously didn't know how to do (or at least not to the degree needed). my recommendations were to verify certain things were in check. i don't feel i crossed the line as no information was given on how to perform the procedures, only that they should be performed. if i were to have said, 'have your service tech make sure that .......' , maybe that would have been more palatable. it just didn't seem necessary to make the 'third person' referrence.
 
#8 ·
I would say low airflow also, but if you would have done your superheat measrements, you would know that. right? I don't know where your at but in a mobile home here, a 3ton is too large for the duct they have in those.
 
#10 ·
Ducts looked fine,velocity at farthest ducts good,no leaks.Suspected low air flow across coil, opened air handler and sealed off blower compartment, and drew air directly across coil.No difference.While adjusting charge noticed too little ref results in frost on evap coil,too much and frost starts at compressor and works back to evap.Started with a perfectly weighed in charge,and adjusted from there.Cannot find a happy medium.Will take my sh/sc measurements when I go back this weekend.

And to all others that contributed to my query,thanks.I am not a diy,have been working HVAC field off and on since 82,and have universal cert.Will apply to pro forum as soon as posts allow.Right now working in Death Valley,hottest place in the country,a real challenge keeping cool!
 
#13 ·
Where did he say that he checked it? What in his post indicates that he knows what it's supposed to be set at? Why didn't he check it first time around? Note he said he'll check it when he goes back. Excuse me for being harsh, but when you have a system freezing up back to the compressor that's a pretty good sign that somebody was ignoring superheat and trying to just get the coil temp above freezing. A tech with 25 years under his belt should know what causes low suction pressure.
 
#17 ·
This is a little off off subject but I see alot of advice being thrown out here and there was a post where the h.o. asked if something was wrong with his system cause his d.a. was a lower temp last year and all i responded with was this isn't a diy site and being nice i asked if he considered the temp/hum was probably different then last year when he checked. My post got deleted and the thread got locked. But People are throwing out ideas and suggestions and it continues. Now this guy does sound legit but this isn't the place. Also to the members who decide pro membership (wink wink nug nug) I requested for it monday. Hope to hear back soon.

Sorry about the venting guys, please continue.
 
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#21 ·
This is just a WAG, but without superheat and subcooling readings it is hard to diagnose.
I am assuming that it is a fixed metering device.

It would appear that you either have an air flow problem as mentioned already or your metering device is overfeeding your evaporator coil. Check metering device again.
 
#24 ·
Results.........



Hi all,
Sorry it took so long for the followup. Most all were right:AIRFLOW! Here is what I've learned,just because a system has been running for several years does NOT mean it was installed properly in the first place,and from now on EVERY time I see a manufactured home or trailer I will check the match between condensing unit and furnace,before making the obvious repair. AR_HVAC_MAN nailed it when he told me to take the furnace #'s and check with MH supply house & against the condensing unit. The HO actually paid extra money for her 5 ton A/C system to make sure she was cool out here in the desert.And the manufacturer took her money and gave her a 5 ton condensing unit and evap coil,but did not upgrade the blower assy! It's a 77k electric downflow,and the cfm rating on high is about 1425(3.5-4 ton max). (By the way that is now the cleanest blower wheel out here):)Upon further investigation they do make a blower assy for a 5 ton unit for that brand.
I am humbled that I missed this,and amazed that the system ran so long under the circumstances. The condensor has an accumulator in it and must have done a helluva job keeping the liquid from the compressor for all this time. Anyway,installed a TXV and minimized liquid in suction line until blower arrives. No more frostback,still low superheat, but better than ice and no s/h. Thanks again for all your input. I'll stop learning when I'm dead!
 
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