ReplyPossibly a little of both, if the liquid line is warm/hot the condenser is probably dirty or condenser fan could be struggling/stopping.
Regular Member
Hi,
Just had a new roof put on my home and noticed the AC seems to be struggling a bit during peak afternoon hours with about a 77 degree indoor setting. 3 ton Carrier Split heat pump system only 2 years old. Single story home, AHU inside a closet indoors.
I'm trying to determine if maybe the new roof (going from 3-tab to architectural shingles) and a 15# felt to 30# felt might be the issue trapping more heat. Same color shingles as before (medium gray). Another change is the ridge vent - used to be a standard aluminum 18 sq in/ft net free air and now is a high-performance plastic low-profile Lomansco with just 11 sq in/ft net free air. When there is wind it pulls well, but in stagnant air it obviously does not have the same net free air space to vent.
The other thing I noticed is the liquid line entering the AHU becomes warm when running at temps over 85 degrees outside. Below 80 degrees the line is very cool to the touch. Is this normal or reflective of a charge issue, TXV issue or dirty outdoor condenser coil fins? (Visually they don't really appear dirty or clogged)
At peak afternoon heat around 90 degrees outside the attic temps are now running about 30+ degrees greater than outside temps. (120-125 range)
SO.....question I'm trying to narrow down is this: Is the AC functioning okay or is the attic just excessively hot due to something related to the new roof, which is then possibly effecting the AC performance? This isn't a DIY but just trying to get a direction on this before calling anybody to look at the situation. I figured the HVAC experts may have ran into this kind of thing before.
Many Thanks,
Sonic
Professional Member*
Possibly a little of both, if the liquid line is warm/hot the condenser is probably dirty or condenser fan could be struggling/stopping.
Regular Member
Fan is fine. On my previous 20 year old Carrier recip I never had to have the condensor cleaned but with these new high SEER Scroll units I'm not sure what is required. Sure looks like a lot more coil fins packed closer together, but then again I can't honestly say I ever paid attention to the old recip enough to be able to say if there was a difference. Is there a particular temperature I should be getting on the liquid line that will indicate if I should call somebody out to check & clean the condenser coils? And would I measure at the AHU or the condenser? Is cleaning part of a basic service call or do I need to specifically request it?Originally Posted by jtrammel
Thanks for the help.
Regular Member
Thread relocated to AOP
Professional Member*
If the air is the same temp out of the registers as before, than hte roof could be contributing, expecially if its' an attic installation. The change in ventilation would be the biggerst change. How many layers of shingles were removed? Additional shingle layers may have acted as a insulator and vapor barrier. A hot roof will drive humidity into an attiuc. IF hte equipemtn or ducts are in the attic, the increase latent load, combiend with less ventilation can make a big difference.
Now if hte air is significantly warmer, then your problem might be the condenser. ALL air cooled coils will need regular cleaning. I don't think the older equipment was any more or less sensitive to air movement across the coil. Higher refrigerant pressures from less heat transfer will result in less effciency and capacity.
It's also possible that yoru system developed a leak and it's jsut a coincidence that your seeing it now.
Liquid line temperatures are useless without knowing the pressures.
AOP Committee/Professional Member*
It is possible there could be a Return air leak allowing hot humid attic air getting sucked into the return.
Record the discharge air temperature coming off the outdoor condenser & then subtract the outdoor temp from it.
For the test to be meaningful, make sure the condenser is clean & dry before running the temp checks below.
At 90F outdoors & 75F & 50% relative humidity indoors the condenser air-temp-split should not be above 17F; @ 80F & 50% indoors the split should not be above 22F. If at 50% indoor RH & those temps, the temp-splits are above the listed split levels, it could be drawing hot air into the Return from a hot unconditioned space, like the attic. Hardware stores usually have low cost humidity gauges, every home needs one.
Especially, if it has a Return chamber under the furnace, every possible entry point must be totally sealed from any source of unconditioned air.
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udarrell
God Speed, Jim. We'll miss you - 2-26-23
I'd say its a combination of a dirty condenser coil. And not enough ridge vent.
Professional Member*
I'm calling a nail in the suction line!
Professional Member*
I had that happen when i lived in a condo. Lineset was run up near the rafters.
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Happened to 2 of our jobs. Roofers claimed no responsibility on either. One one they hit the suction line in 3 spots.
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Last edited by beenthere; 05-25-2013 at 06:43 PM. Reason: Non Pro * Member
God Speed, Jim. We'll miss you - 2-26-23
Homeonwer314, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.
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Regular Member
Many thanks to all who replied.
To clarify: One shingle layer, attic ducts, lineset under ground (under the slab).
I suspect a combination of slightly dirty condensor mixed with ventilation that is just not keeping up. Now, could be NEW heat generated by the new roof or it could be the SAME heat just not ventilating as well with the new ridge vent.
Not sure this provides a clue or not, but once the attic and outside cools to 80 degrees or less the A/C blows very cold as usual. It is when the attic starts exceeding about 110 degrees and the outside exceeds about 85 that the air from the ducts is not quite as cold, and so the system starts running a lot to keep up. It is still very cool, but not quite as cold. Perhapes I should do a Delta T test from intake to exhaust on the AHU?
The other possibility, as somebody pointed out, is maybe a slow leak. I did notice something today that I do not recall seeing before... On the liquid line where it connects to the drier outside of the condenser I am seeing what looks like little "blisters" in the copper at the braze joint. Would this by chance be a symptom if Puron had been slowly leaking? I will try to take a picture and see if I can figure out how to upload it....
Professional Member*
its probably just excess solder on the joint, but a picture would confirm.
Heating/Cooling Services Inc.
www.heatingandcoolingservicesinc.com
Regular Member
If you mean "bumps" or "lumps" that sometimes are seen on/near a solder joint, it isn't that. It literally looks like something blistered the copper. Tomorrow I'll take a pic.....
Professional Member*
sounds interesting
Heating/Cooling Services Inc.
www.heatingandcoolingservicesinc.com
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Sure would have been nice if you could have gone with a "cool roof" material. If you can't get the ducts out of the attic, and you can't insulate the roof deck, nothing beats a cool roof for reducing attic temperatures.
That said, if you haven't had your a/c serviced for the summer, do it now. If you get it working in tip top shape and it still seems to underperform on hot days, you then know your new roof and/or ridge vent may be the culprit. I'm not all that confident ridge vents reduce attic temps all that much, but they are better than nothing.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Regular Member
It would help if I had an idea of what a "normal" temp is for an attic in Florida with passive ventilation. Right now, I am seeing a 30 degree delta between the attic and the outside temps when at the peak heat of the day lately (about 90 degrees outside). So I'm reading ~120 degrees which seems ridiculously hot to me. I don't recall the attic feeling that hot before but then again I never measured it previously. Attic is about 10 feet high and I'm measuring at mid height, but higher up at the peak of the roof I bet the temp is at least 5 degrees hotter yet. Can't imagine what is going to happen when we get to the 95-100 degree range soon with high humidity....
Professional Member*
Attic temps are mostly driven by the solar heat gain on the roof. The attic temp when it's 90F outside isn't a lot hotter than when it's 85F outside.... probably just 6-7F hotter in the attic. Humidity doesn't drive attic temps.
"cool roof' desings unfortunatly are pretty foreign to most roofers. Plus it's more expensive for the homeowner even though steel roofs last a lot longer and ithe cost difference will pay for itself within probably 10 years... less if you can use tax credits.
Professional Member*
What gets lost in discussions concerning ventilated attic air temperatures is the surface temperatures of the roof deck, roof trusses or rafters, and the exposed surfaces of insulation on the attic floor, and the ducts in the attic. If you are seeing attic air temperatures around 120 degrees F, you can be confident the roof deck is much warmer than that. In turn, that hot deck radiates directly down to the insulation and ducts, heating them up in the process.
By increasing attic air ventilation, it may reduce air temperature, and provide a small heat sink for the ducts and attic floor insulation to dump their surface heat into, but by far the greater heat sink all of this heat WILL migrate toward is the cool interior of your house, and the cool air traveling through the ducts.
In your case, while it may be true your old ridge vent worked better than what you have now, what may be worse is that your new shingles soak up more heat than the old ones did, for whatever reason. You did mention that you went from three tab to architectural shingles. I have no data at the moment to support my notion, but I would be curious to know if there is a difference in the emissivity and reflectivity characteristics between what you had before and what's up there now.
Regardless, get your a/c system serviced and cleaned. You need a reference point to determine which component is at fault; the new roof or the a/c.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
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