Hi, After days of lousy wet weather sun came out today and got hot. a/c just kicked in this afternoon. Air cleaner is cleaned, filter is replaced. All looks, sounds alright. Measured temp. between cold air coming out and warm air returing at the upstairs registers. ~17 deg. F Is it Okay? Or need to call for service? TIA,
Hi, Sorry I meant to say the temp. diffrence between two reading is ~17 deg. F.
That's a bit on the low side. If it's not a relatively new "high SEER machine," the air one the cold side of the air handler should be between 40F and 50F. (Older machines keep the humidity down by cooling down to 40F. Newer machines don't take out as much moisture but make it up by handling more air.) If the air is quite "moist" the outlet temperature will be higher. The machine can't outlet air cooler than the "dew point" of the exhausted air. If there is a lot of moisture in the house, it might take a day for the machine to bring down the humidity before it can do the serious cooling. You can check to see whether condensate is coming out of the air handler. No condensate and relatively 'warm' air (60F or higher) usually means the machine isn't doing much.
Unless the air intake is really, really poorly positioned, it should be sucking up "warm side" room air somewhere in the high 70sF.
Doing the math says that your machine ain't acting right.
Obviously, you are trying to save the cost of the repairman. You may have poorly insulated ducts which means that the cooled air heats up between the air handler and your rooms. That's why I recommended measuring the temperature at the air handler. (you can drill an access hole in the duct work for your probe and cover the hole with metal duct tape when you finish.)
If it keeps you comfortable, then I guess it's "gud enuf." If it doesn't keep you comfortable, call the repairman.
Hi, Thanks for the heads up.
When was your system last cleaned by an HVAC company tech? If the condenser fins are clogged or dirty, the AC will be less efficient.
TDD
True, BUT, the OP didn't say how long the machine had run before making the measurements. It may take an hour or more for the AC to cool the ductwork.
No (reasonable) A/C can drop the temperature of 130? air to 50? immediately. You cannot judge an A/C by the temperature of the conditioned air alone without knowing the temp of the incoming air.
You ought to let it run for a couple of days first; as someone said, you not only have to cool the air but also the ducts themselves and anything else the air touches before it reaches your vents.
If the ducts run through the attic you also might to have a look to see if something came loose during the winter, or if some creature knocked a hole in the ductwork. A couple of years ago a worker in the attic (working ON the A/C!) knocked a fitting loose and there was a gap where the duct attached to one of the vents.
Shaun Eli
Copyright 2010 by Shaun Eli. All rights reserved.
I concur, Doctor. The system should be cleaned. The tech should shut off the power, pour on purple liquid, wait, rinse, repeat. Should ask to use your garden hose. Ask him (her?) to spray the side of the house occasionally. That cleaning stuff can damage house siding.
Could also be low on freon. (Bad thermostat joke to follow, sure enough.)
For most residential AC, a Delta T of 20 degrees is mighty good. You're close. There is no such thing as a delivery temperature indicating a good working system, it all hinges on the degree change before and after the coil.
I went to the home of one of my commercial customers Saturday to install a wireless N router for his computers. Sunday morning he calls me about one of his AC units not cooling. I walked up to the condenser and heard a humming sound and sure enough, the combo capacitor was bad. The top was popped up on that damnable Chinese capacitor. It was a 440 volt cap too. He lives out in a semi-rural area and I'm going to recommend surge arresters for the heat pumps.
TDD
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