We have an old Ruud central air conditioning system from around the early 80's. The few past years we have noticed that the system is constantly running and taking longer than it should to cool the house. So thinking that it was low on refrigerant, we had someone check the system 2 years ago and they said that it had enough pressure. So this year I took a temp probe that I use to diagnose air vents in a car and placed it inside one of our vents. It is reading about 60 degrees. Now I know on a car that 60F degrees is high and it should be reading between 40F-50F degrees. Does the system appear that it may be low on refrigerant and should I get someone else to check the system?
I think the standard is a 20-degree drop. If ambient air is 80, then cooled to 60 is good.
During the intervening years, your insulation may have settled, or some other problem involving leakage. Sounds like the A/C is doing the best it can and the problem might be elsewhere.
Nick, the issues are much more complex than measuring delivery temperature. I don't know where you get your car information, either. If an air conditioner can drop the temperature 20 degrees, it is doing about all it can. Get two thermometers - measure the temperature going in the return air grill and the temperature coming out of the closest supply grill. If the difference is 15 to 20 degrees, the unit is working. If the Freon line outside is sweating, it is a good indication that the gas is close to right. If it is not sweating, you have a problem. If it has a sight glass installed and you see bubbles going by, you have a problem. The air that the fan is blowing out the top of the condenser should be notably warm to hot. The condensate line should be delivering a steady stream of water If you live in a humid climate, it will be quite a heavy stream.
Things to check:
Clean the condenser, this involves removing the top of shroud, using coil cleaner, rinsing from the inside to the outside. Just washing it off with water is not enough, but it would sure help.
Check the filter on the inside. Change the filter anyway.
The most likely suspect is leaking duct work or fallen away insulation on the duct work.
This is all an oversimplification, but should give you enough advice to understand what a HVAC tech is telling you.
snipped-for-privacy@nowhere.com wrote in news:vmnl445t8qj839invl2fpvj04s3tgqlh3i@
4ax.com:
First, I'm not an AC wiz, tech, whatever. Just my experience with several AC systems in houses I've restored in the past few years and conversation with an 25yr AC company owner.
As said, the temp differential is what you look for - the difference in the air temp entering the return vs the temp coming out of a vent. Also as said, there are many factors. Shortest run vent will likely have the coolest air coming out, especially if ductwork is in attic.
Brand new system, 25 degrees is excellent.
Existing system let's say less than 10 yrs old system in good shape, 20 degree differential is excellent.
Older system maybe 15 yrs old, 15/16 degrees is good. Unless it needs cleaning, filters, etc. not worth spending lots of $ to try to get it any higher.
Other factors - ductwork in an attic vs crawlspace vs indoor main trunk. Temps of any system will vary in the same system depending on surroundings. For instanceworst case where the ductwork is in attic and the unit is sitting in the afternoon sun on a hot day, you can see quite a difference in the differential in the morning vs the afternoon. Had this one myself with a heat pump. 20/21 degree differential in the morning/late evening vs 11-12 degrees differential at 4pm on a 100 degree day. Coil in superheated attic, ductwork in attic, unit sitting in sun on
100 degree day.
Refrigerant is not the only possible cause. "DanG"'s reply gave you some good tips. Since you had an AC guy come out, assume he checked those things? Crudded up condenser has a big effect and an older system has a much higher probability of that. Less common but possible is a leak in the return in the attic or return side of the attic unit and now it's mixing 130 degree air with 78 degree air and trying to cool it.
Just my unofficial .02.
Red Green, Professional....wana-be. PhD, School of Hard Knocks
Ruud's are notorious (with it's louvered sheetmetal cover) for clogged coils. and somewhat of a pain to open up. I opened mine up after several years (we have a cottonwood) and there was a blanket of fuzz an inch and a half thick. worked much better with that cleaned off.
It would be wiser to spend the money on additional insulation, upgraded windows and doors, insulating drapes or blinds, etc. That would give substantial savings in heating bills as well as cooling. Depending on the upgrade, insulation improvements can pay back in less than a decade. I completed my home energy upgrades 4 years ago, and pay 1/3 as much in utility bills as I did in 2003, even with intervening rate increases. The house is also much more comfortable to live in.
Wow! That's really good. We've managed to cut our consumption by almost half, but you've got us beat. On the other hand, we didn't spend much money -- mostly just sealing ductwork, replacing incandescents with CFL's, and installing (and using) a programmable thermostat.
Thanks for all of the responses. I have measured the temp on the intake by the attic door and it is reading at 75 degrees. The temp coming out of the top floor closest to the unit is 62 degrees.
I replace my filters once every month. I'm going to be ordering the polyester filters that have a better merv rating than the fiberglass ones I have been using.
I don't know when the condenser coils were last cleaned so I'm going to be looking there. If anyone has any sites that are good at showing step by step on how to clean them, I would appreciate it.
It's all relative. This house was built in 1971, and had never been upgraded. I installed a heat pump in 1995 (the old furnace was forced air electric), blew in attic insulation in 1996, put in U .36 windows in about 2001, then in 2004 we remodelled, including subfloor insulation, more attic insulation, attic fan, insulated entry and patio doors, insulated all the water lines, and installed energy star appliances. While the walls were open, I ran around and foamed all the plate and plumbing penetrations with foam caulk. We also installed a generator transfer switch. We are the last house on the power line, and have a history of power outages lasting several days.
My wife found these nifty insulating blinds that are kind of like a honeycomb an inch thick that fit inside the window trim like a mini blind. They are translucent, so they let light in, and are white, so they reflect heat. They are mostly air, so when you raise them up they only take up about 2 inches of space at the top of the window. Combined with the efficient low-E glass, they button things up nicely. We replaced the old aluminum slider patio door with a Pella french door that has the mini blinds in between the double glazing panes. I also added an open porch roof to the west side of the house that shades that wall on hot afternoons.
The next step is solar hot water. We don't have a great solar site, but we do have wood heat. I figure between coils on the roof and coils behind the wood stove, we could produce 80% of our hot water for free. Someday I want to add another layer of insulation on the walls and install cement board siding, which would turn the outside walls into a thermal break system.
Down the road I would like to install a high pressure gravity feed water system. We already have a low pressure system with about 10 feet of head. A power outage means we lose most of our water pressure, but not all of it. You can still flush a toilet or fill a bathtub. We have decorated the house with brass candle sconces and wall mounted oil lamps. When the power goes out, we can light the house, do dishes (by hand) and cook on the wood stove. The insulation upgrade means only about a 15 degree temperature drop from one end of the house to the other in freezing weather.
Energy upgrades don't all have to happen at once, but they are a gift that just keeps on giving.
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