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maverick06 07-28-2007 10:53 PM

help, Poor performing AC, coolant leak? damaged coil? images
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I am looking for a bit of assistance. I am a mechanical engineer, but I dont know much of anything about HVAC. But I can diagnose a bit.

My AC has been not performing well this year. It downright sucks. I bought the house about a year ago, and the AC was working then. Right by the interior heat exchanger there was a humidifier for heating, I removed it as a) its unhealthy to use and b)lots of AC leaked past it and I didnít want to lose that cooling power. While removing it I noticed that the heat exchanger was beat up a bit, I donít think I damaged it, but I may have. (it appeared to have the lower tube sliced open, see picture below) Regardless the AC worked fine last year after I removed it, as best as i can remember.

This year the AC is near worthless. The intake air is 85F and the output is 75F. It cannot keep the house cool, not at all.

So this morning, I removed the sheet metal I had covering the old humidifier hole. The lower quarter of the coil was iced up. I have a clean filter in and all registers wide open, so there is plenty of airflow. the condensate drain is clear so that should not be a problem.

Running the AC with the panel, it was easy to see that there was condensation forming on the coil and freezing. Using my IR thermometer I was able to find out the following. I donít know what it means, hopefully someone else does.

ambient temp: 80F
outside temp: 80f
non running coil temp: 76F

the temperature in the interior coil was measured top, 1/3 down, 2/3 down, bottom.
top: 77
1/3 down: 77
2/3 down: 65
bottom: 25

there were also 2 tubes for the coolant to go through. The warmer I assume to be the exit. the two tubes were 72F and 20F.

over the course of 45 min the house temp dropped 0.5F and the humidity dropped 8% relative humidity.

I am guessing that the system is low on coolant. And I am wondering if it leaked through the gash in the coil (pictured below). But the gash is so big that I would have thought all the coolant would have leaked out nearly instantly. I saw it there over a year ago and it seemed to be working later that summer. I also saw no obvious oil/grease marks around the gash which supposedly are indicative of a leak.

What do you, more experienced people have to say about all this? Any opinions? How can I be looking INTO a tube on the heat exchanger and not have lost all my coolant after it sat for over a year?

And most importantly, what do I do now? Replace the coil? get a recharge (about how much does this run)? The AC unit is a 1991 that uses 40 amps (I am not sure it's cooling capacity). It might just be time to get a whole new setup, but thatís not cheap and why i would like to avoid it...

Thank you so much for all your help!

bigMikeB 07-29-2007 06:41 AM

The unit is low on freon, have someone come out and do a leak check/repair and you should be back to norm.

maverick06 07-29-2007 11:49 AM

any idea what that typically costs?

bigMikeB 07-30-2007 05:01 PM

It depends on the area you are in and the type of company you call. In my area a union company would be in the $400 range for a leak check a flat rate priced company would be looking for @$100 for a show up diagnosic charge and @$500 for a nitrogen leak test, the repair would vary with both depending on what is required to fix it.

maverick06 07-31-2007 05:19 AM

wow, good bit higher than I expected. Thanks for the input! I think I am better off just getting a whole new unit as opposed to pouring money into something from 1991...

bigMikeB 07-31-2007 05:30 PM


Originally Posted by maverick06 (Post 55431)
wow, good bit higher than I expected. Thanks for the input! I think I am better off just getting a whole new unit as opposed to pouring money into something from 1991...

Keep in mind the new units are a higher SEER, meaning you will have to change the indoor coil and some sheetmetal (they are much larger), and the lineset when changing the condensing unit.

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