Measuring A/C Temp Solved, sort of...

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On 6/2/2015 4:47 PM, Ashton Crusher wrote:

Well, certain to happen before too long. Just add a couple pounds of that freon stuff, and it will be just fine. Someone had to say it.
I stand by my original diagnosis, and also my offer to come out and fix it.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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On 6/2/2015 12:24 PM, Boris wrote:

The condenser is clogged with dust, and needs to be professionally cleaned. Use the purple stuff. Any good tech would have picked up on this very simple diagnosis in a few minutes.
Gee whiz, you told the entire class what was wrong, wonder if I'll be the only simple minded (but excellent quality) AC tech to pick up on the answer you handed us on silver platter.
Your guy and tech support "baffled". What a bunch of maroons.
BTW, remit $147.50 for consultation. I also make house calls, buck a mile (one way) from western NY, USA.
I have an uncle in Los Angeles who would love to have me visit.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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On 6/2/15 10:34 PM, Stormin Mormon wrote:

Maybe he was baffled because he knew the condenser was cooling properly. Don't you think he checked the temperature of the outlet, with a thermometer or by touch?
If the condenser were dirty enough to overheat the compressor, how would he get a 16F drop when it was restarted? Why would it work fine for an hour or so?
If there's moisture in the freon, most would probably pass through the expansion orifice. It might take an hour for enough ice to build up, to block it enough to overheat the compressor. As soon as the compressor stops, the indoor blower heats the evaporator to 74. No more ice. The tech starts it can can't find anything wrong.
BTW, remit $247.50 for insultation by insinuation.
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On 6/3/2015 12:05 AM, J Burns wrote:

CY: And how would the OP know that?

CY: Possibly, but he needs more data to tell if the condenser is cooling properly.

CY: Because the compressor discharge can be up to 250F (not often, but now and again I see temps this high). The outdoor air is 80F or so, and the condenser has time to cool from 250F (at the discharge) to 80F or so. After an hour of pumping heat into the condenser, the condenser temp goes up again.

CY: I read the OP message, and got a totally different diagnosis from what he wrote.

CY: I can get insulted for free, I'm not paying. But, the OP can't even pay for a correct diagnosis, which makes me very valuable. I even also offered to go fix it for him.
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On 6/3/15 7:22 AM, Stormin Mormon wrote:

The OP didn't say he knew that. He said only that they were baffled.

What data? If the outlet tube is close to ambient, the condenser has cooled the freon about as much as possible.

It can cool faster when it's running, with all that 80 F air being blown through it. The specific heat of copper is 0.09 btu per pound per F. On a 24,000 btu unit, do you really think it would take an hour to overheat if the blown air weren't doing the job?

That's because you're not experienced. Back when I was inexperienced, in 1997, my niece borrowed my car. She reported that the AC was feeble. I tried it and it was fine.
Ten years later it happened to me. It started cooling fine, then all I got was warm air. When I tried it a few minutes later, it worked fine and didn't quit.
Both incidents happened the first time it was used in the season. The owner's manual says to run it for a 15-minute period each month, but I forget. I believe moisture can migrate out of the drier, and running it every month puts it back into the drier before there's enough to ice the orifice. The problems I had at the start of two seasons solved themselves when the ice melted and the system put the moisture back in the dryer.
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On 6/3/2015 1:01 PM, J Burns wrote:

CY: I'm getting lost in the layers of quotes.

CY: Be nice to know the inlet tube temp.

CY: I'd expect the unit to over heat in much less than an hour.

CY: Oh, I'm not experienced. Well, that explains a lot. Hey, you want to tell me how long I've had my EPA card, and how long I've been working on central AC systems?

CY: I forget stuff, also.
I believe moisture can migrate out of the drier, and running it

CY: As an inexperienced hack, I've also learned that it takes a while to get an idle system going again, but it's got nothing to do with internal water, or putting moisture back into dryer.
CY: Gently put, my understanding is considerably different than what you're writing.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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On 6/3/15 2:07 PM, Stormin Mormon wrote:

A condenser can cool only down to the ambient air temperature. I believe the OP said it was 80F. If the outlet tube is close to 80, the evaporator has cooled it about as much as possible. What does the inlet temperature have to do with it?
If it read 90F, I would see if I could gain efficiency by cleaning the fins, but I would not expect that outlet temperature to overheat the compressor. It would be equivalent to running the system when it was 90F outside with a condenser that cooled perfectly.
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On 6/3/2015 9:33 PM, J Burns wrote:

It's nice to know the temperature drop across the coil. That's a good indicator how well the coil is working. Also, nice to check the surface temp of the coil near inlet, and different places on the coil. See if most of the cooling happens in the first third or half, for example. Plenty more data to be had.
. Christopher A. Young learn more about Jesus . www.lds.org . .
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On Wednesday, June 3, 2015 at 9:33:11 PM UTC-4, J Burns wrote:

I would think 90F coming out of the condenser when it's 80F is probably normal. On AC units that I've seen, the pressure line even all the way back at the air handler, is still just slightly warm to the touch. Whether it's 80F or 90F it still going to drop a lot when it expands.
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On 6/4/15 8:57 AM, trader_4 wrote:

Looks like you're right again! http://www.achrnews.com/articles/91476-condensing-temperature-clues
I was impressed at how low my split was, but now I don't remember the figure. My AC season hasn't started. When it does, I'll check.
If it's too low, now I know it's a sign of trouble.
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On 6/4/15 1:24 PM, J Burns wrote:

Uh-oh, I misunderstood. Condenser split is the temperature at which the refrigerant condenses. I guess that's deduced from pressure. The temperature at the outlet would be lower than the condensing temperature.
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On 6/4/15 2:42 PM, J Burns wrote:

I still didn't say it right! It's the condensing temperature minus the ambient temperature.
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Well, I'm going with the easiest thing to eliminate, first. I'm going to clean the compressor before considering a new unit.
I did call another a/c company in the Sacramento area, and talked with their tech, and he advised cleaning the compressor and see if that helps. I asked him if he could get out there and do the cleaning, but he's booked for a while, and I've got some visitors coming in one week.
One problem I may have is that the back side of the unit is less than 12" from the side of the house. The tech suggested that I remove the top of the cabinet (and the other three sides), and perhaps I can get to the inside of the backside fins, and using a spray hose, force any debris/dirt from the inside, out.
I'm going up early Friday morning to clean the thing. By the time I finish cleaning, it probably won't be hot outside, so I'll have to lower the thermostat to get the unit to run. Then I'll wait.
If it wasn't for the mileage charge, I'd have you out. <g>
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On 6/3/2015 11:24 AM, Boris wrote:

Maybe we can go metric, and have smaller miles?
I'd suggest to clean the condenser (fins and tubes) rather than the compressor (the big tin can in the middle). Please keep the compressor and wires dry.
I looked online, about a thousand dollars air flight, change planes in Chicago. Food, car rental, motel. I could do it for about two and a half grand. Leaves some money left over for labor charges.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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Yes, I've gotten my terminology mixed up. Just like learning how to maintain the pool equipment from knowing nothing about it at first, to being able to take care of it myself, between this ng, talking with service techs, and going online, I've learned a lot about proper a/c terminology and how it all works.
All along, I thought the cooling took place in the outside unit. Wrong. I didn't know there was a thing called an evaporator in the furnace...a split system. I though that if I took the fan off of the top of the a/c unit, I'd see a whole bunch of complicated stuff about which I'd know nothing. Now I see that all that's in there (besides the electronics, which are physically isolated from the inards) is a compressor (big tin can in the middle) sitting on some rubber vibration isolation bumpers, surrounded by a radiator-like set of cooling fins.
I was incorrectly using compressor and condensor interchangeably.
The theory we're working on now is that the condensor is too dirty to cool the returning hot air generated at the evaporator. Yes?
If that's not it, I would suspect the evaporator. I'll have to see if I can get at the evaporator, and if so, I'll clean it, too, and reseal.
While the tech didn't record all the data on the work order, as he checked items, he'd tell me this is in range, that is in range. He did check temps at the evaporator inlet (he didn't open up), and considered icing.
I bought four cans of consensor foaming spray cleaner yesterday, but now can't go up to the Sacramento area until Sunday. Because the unit has louvered side panels over the fins, I don't expect to find and bent over or dented fins.
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On Thursday, June 4, 2015 at 11:35:39 AM UTC-4, Boris wrote:

That's the theory some are working on. I'm with Mr. Burns and doubt it's the issue. If the condenser can't cool sufficiently, then the pressure line going back to the furnace will be significantly above ambient. If it's barely warm, then it has been properly cooled by the condenser and I don't see how cleaning is going to solve it. Any competent tech could tell if the line is abnormally warm by just touching it.

I doubt that's the problem either, but if you can DIY, no harm in taking a look.
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Got it.

You know, while I thought the tech said this was fine, I don't remember. If it was fine, then, yes, I probably have other than compressor/condenser problems.

While it may come down to a major repair or replacement, I just dont' want to do that until I've convinced myself it's needed.
Thanks.
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Boris wrote:

If I were you Boris, first when it is running make sure the condenser fan is running, spray water onto condenser to aid cooling, then watch, does it keep running without tripping off? Fan must stay running while cooling(should never stop). Cleaning condenser is not hard. Just remember you have spray water inside out to purge dirt.
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Tony Hwang wrote:

My second hunch is for some reason I'd replace main contacter inside ODU.
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On 6/4/15 1:07 PM, Tony Hwang wrote:

I replaced mine in 2011. There were so many wires connected that I drew a diagram.
I was lucky. I kept the probe of an indoor/outdoor thermometer in a register because the air temperature gave me a rough idea of the dew point. (It's not the heat, it's the humidity.) I happened to see that the air temperature didn't rise after the thermostat shut off. I ran to the window and saw the compressor still going, so I shut it off at the breaker box.
I believe contactor contacts are coated with silver. Over the years, it can disappear. Then they can stick. If the compressor keeps running without the indoor blower warming the evaporator, the compressor can be wrecked.
I wonder how often a stuck contactor is the cause of a wrecked compressor.
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