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Started By
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Old AC unit (~32 yo) not putting out. Replace?
Posted on 5/26/21 at 3:47 pm
Posted on 5/26/21 at 3:47 pm
I guess replace it is the obvious answer, but I've had several techs check it and the damned thing seems to be in perfect condition. Refrigerant pressures check out perfect, compressor works fine, it moves air perfectly (except my return may be a little undersized). The only thing is the air coming out of the vents is never colder than 70 degrees on warm days, and it struggles to bring the humidity down no matter how long it runs. Electricity bills are never outrageous.
I think the only thing that hasn't been checked in a few years is the condition of the evap coil, but it's not leaking. Could it just be chock full of shite? I've been here just over 2 years so I don't know the last time it was cleaned, and every time I've asked about it they don't seem too keen on taking a look because it's caulked shut, and no one has seemed worried about it. Should I have demanded they crack it open? Should I do it myself? Or just say frick it and replace?
I think the only thing that hasn't been checked in a few years is the condition of the evap coil, but it's not leaking. Could it just be chock full of shite? I've been here just over 2 years so I don't know the last time it was cleaned, and every time I've asked about it they don't seem too keen on taking a look because it's caulked shut, and no one has seemed worried about it. Should I have demanded they crack it open? Should I do it myself? Or just say frick it and replace?
10
Posted on 5/26/21 at 3:54 pm to Korkstand
Sounds like beyond borrowed time IMO. If you can swing it, I'd replace.
Posted on 5/26/21 at 3:56 pm to Korkstand
quote:
Electricity bills are never outrageous.
I thought the same until I replaced my 20+ year old unit. My electric bill dropped $80 a month.
Posted on 5/26/21 at 4:07 pm to RaginCajunz
quote:I like to borrow as much as possible.
Sounds like beyond borrowed time IMO.
quote:I'll probably end up replacing, but I like to ask questions to help me through the next few decades of dealing with AC issues. Just seems like if nothing is obviously wrong with it, there must be something subtly wrong. "It's just old" bothers me.
If you can swing it, I'd replace.
This post was edited on 5/26/21 at 4:10 pm
Posted on 5/26/21 at 4:11 pm to Korkstand
They should be able to see the evaporator by removing the filter and using a light I would think.
How is the air flow coming from the vents?
How is the air flow coming from the vents?
Posted on 5/26/21 at 4:26 pm to Shexter
quote:This is a 2.5 ton unit that services 1,400 sqft, and I have a 4 ton unit that services the other 2,000 sqft (this unit runs great). Bills usually top out right at $300 during the hottest months, and $150-200 otherwise. If I could save $80 for even half the year, it would be a no-brainer to replace. Probably a no-brainer regardless, but it still nags at me that all the vitals are fine but it still struggles.
I thought the same until I replaced my 20+ year old unit. My electric bill dropped $80 a month.
I guess I will check out the evaporator myself, and also put in a deep filter to help out the return issues, and hopefully help it limp through the summer and replace this winter so the installers won't be so mad at me.
Posted on 5/26/21 at 4:30 pm to ItzMe1972
quote:Nope, my return goes up through the wall then 90s over in the attic to the air handler.
They should be able to see the evaporator by removing the filter and using a light I would think.
quote:It's got decent flow, it's just ~70 degrees (my other unit puts out 55 degrees at the vents). Dampers have been verified correctly adjusted on several occasions.
How is the air flow coming from the vents?
Posted on 5/26/21 at 4:37 pm to Korkstand
Spray those coils down with some of this:
Posted on 5/26/21 at 4:54 pm to Korkstand
quote:
I think the only thing that hasn't been checked in a few years is the condition of the evap coil, but it's not leaking. Could it just be chock full of shite? I've been here just over 2 years so I don't know the last time it was cleaned, and every time I've asked about it they don't seem too keen on taking a look because it's caulked shut, and no one has seemed worried about it.
You should absolutely clean the evaporator coil. It's crazy the tech didn't check it. Cleaning the coils should be part of your regular maintenance routine.
Posted on 5/26/21 at 5:02 pm to Korkstand
quote:Yes, replace. I hear it's expensive but usually worth it.
Old spousal unit (~32 yo) not putting out. Replace?
Posted on 5/26/21 at 5:29 pm to Korkstand
quote:
Just seems like if nothing is obviously wrong with it, there must be something subtly wrong. "It's just old" bothers me.
stop tripping, until it breaks roll with it unless the electric bills are killing you.
put the money aside to replace it but wait until something major breaks. that old unit may outlast the new one you replace it with today. units today arent made very well and only designed to last 5 yrs, those older units were built and made to last forever
Posted on 5/26/21 at 6:11 pm to TAMU-93
quote:I just spent the last hour up there trying to access it myself, and I see why no one wants to touch it. I have no idea how typical this is, but let me describe:
You should absolutely clean the evaporator coil. It's crazy the tech didn't check it. Cleaning the coils should be part of your regular maintenance routine.
It's a horizontal unit, blower->gas furnace->evaporator->duct box. There is a transition piece between the furnace and evaporator, and it is screwed and caulked to hell at both the furnace and evap ends. Similarly the duct box is screwed and caulked to the other side of the evaporator housing. It took me about 30 minutes to scrape off enough caulk, and peel apart 1 corner of the transition piece and lift the top of the evap housing enough just to see the "in" side of the coil. It looked relatively clean, not much corrosion and it wasn't caked up with mold or anything like some photos I've seen. It had been running a while and didn't have any condensation that I could see, though.
The housing is only about 6" thick, so I guess it's just one set of coils.
I might try to crack open the other side tomorrow to look at the "out" side of the coil. I'm telling you though, it's going to be a pain in the arse.
Posted on 5/26/21 at 6:29 pm to Korkstand
I’d like to bum off this thread. The feels like temp is 95 right now and my unit is only getting to 77. Is there something probably wrong with it or is it just so darn hot that the temp differential reached its limit?
Posted on 5/26/21 at 6:45 pm to keakar
quote:That's my usual MO.
stop tripping, until it breaks roll with it unless the electric bills are killing you.
quote:I guess that's why I'm trying to troubleshoot so hard. Does a pressure check tell you if the expansion valve is alright?
put the money aside to replace it but wait until something major breaks. that old unit may outlast the new one you replace it with today. units today arent made very well and only designed to last 5 yrs, those older units were built and made to last forever
Posted on 5/26/21 at 6:53 pm to Korkstand
Your system sounds like mine, with a horizontal slab style evaporator coil. You should be able to remove the front panel where the refrigerant lines enter the unit. The screws might be covered by aluminum tape or something.
Posted on 5/26/21 at 7:54 pm to Korkstand
quote:
I guess that's why I'm trying to troubleshoot so hard. Does a pressure check tell you if the expansion valve is alright?
expansion valve is just a pressure regulator, if its not working right it wont cool properly or at all
This post was edited on 5/26/21 at 7:55 pm
Posted on 5/26/21 at 8:16 pm to Korkstand
Congrats on getting 12-17 years more than it’s design life
Posted on 5/26/21 at 8:22 pm to keakar
quote:Right, but I'm asking if a bad valve could be diagnosed when they check refrigerant pressure at the condenser?
expansion valve is just a pressure regulator, if its not working right it wont cool properly or at all
Posted on 5/26/21 at 10:35 pm to Korkstand
quote:
Old unit (~32 yo) not putting out.
So, my wife?
I'll see myself out.
But really, I thought my units lasting 28 years was impressive before we replaced them. Bite the bullet and get a multistage.
Posted on 5/26/21 at 10:41 pm to Korkstand
quote:
It had been running a while and didn't have any condensation that I could see, though.
Well that seems to be an issue, but I’d have the evap coil cleaned thoroughly, seal it and then check refrigerant pressures, superheat, and subcool values - more important numbers than just refrigerant pressures when diagnosing whether or not the system is properly charged or if there is a restriction in the system. Need to check temperature in the supply plenum right after the evap coil after it’s sealed up - typically a hole is drilled in the plenum in front of the coil, temp checked, and hole sealed. If for example you are getting a 55 F temp in the plenum, but 70 F from the supply register(s) then you might be looking at supply duct issues.
Return, supply, and total external static pressures are also helpful diagnostic numbers to troubleshoot potential air flow issues.
Problems with an expansion valve can often be troubleshooted by a skilled HVAC tech from subcool and superheat temperatures. On a system that old you likely have a piston (fixed office) - sometimes the wrong size is installed. Could potentially have a capillary tube refrigerant metering device in a system that old.
What you really need is a skilled HVAC tech with a diagnostic mindset and excellent diagnostic skills. Sure your HVAC has far outlived it’s expected service life but that doesn’t mean it is not fixable or has some useful years left in it.
This post was edited on 5/26/21 at 11:08 pm
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