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

[Boris]

On 5/5/2015 I sent out a note about my air conditioner not cooling after being on for a long period of time. I had to drive up to the Sacramento area yesterday and meet an a/c tech during the late afternoon, when it got hot (but only 80 degrees outdoors), to demonstrate what was going on. He figured it out. I had kept outdoor/indoor/thermostat/vent temperatures for four days running, and noticed a pattern...cold air blew for a while, but after an hour or so, no matter the outside/indoor temperature, or thermostat setting, 74 degree air began to blow.

Whe the a/c first goes on, it blows 58 degree air and begins to cool the house. (I hung a digital thermometer on the overhead vent.) If the house isn't too hot, it gets cooled down properly and the a/c turns itself off. If the house is hot, the a/c begins to blow 58 degree air, but after a while (maybe an hour or so), the fan continues to blow, since the thermostat is still calling to cool more, but the compressor turns off. All the while, I thought the compressor was still going, because air was blowing out of the vent, but the air was 74 degrees.

Yesterday, I turned the a/c on at 2 pm, and the house began to cool with

58 degree air coming from the vent. The tech arrived at 3:15 pm, and just at that time, I showed him that the vent air was now blowing at 74 degrees. He went outside to the a/c unit, and noticed that although air was blowing out the indoor vent, the compressor was not running as noticed by the fact that the fan on top of the unit was not running. He measured all the amp/volts at the two main capacitors (start and run capacitors) and all was fine. He measured the freon, and it was up to capacity. He then measured the temperature of the compressor, and it was HOT, at 149 degrees. He called back to his company and also to the American Standard, the a/c manufacturer, for advice/trouble shooting. All were baffled.

He then took the garden hose and ran water over the compressor cooling fins, and the compressor started right up and the vent air went from 74 to 71 degrees in a minute, and continued to decline. He surmised that the compressor was overheating and was shutting down, as it should. But, no one knows why the compressor gets so hot. The outdoor temperature was only 80 degrees yesterday. Even if the outdoor temperature is 75 degrees, the compressor gets hot after running for a while and shuts itself off.

The a/c unit is an 18 year-old American Standard model 7A2042A100A1, R22, used to cool a 1700 sq. ft. single story home in the Sacramento area. This is my dad's house, who passed away in late 2013. Beginning in 2012, he used to call me up to figure out why the house didn't cool properly. We had techs out, and they replaced this and that, but still no luck. I replaced two thermostats, thinking that may be the issue, but still no luck.

A month ago, when the tech thought the problem was with the a/c fan, because it was VERY noisy, he replaced the fan and capacitor for about $500. But, warm air still blew.

So far, the tech can only explain this by saying that the unit is old, and just doens't run as efficiently. While I can buy this, I don't know why this would be. Anyone?

At any rate, to replace the compressor is about $2500, which I could do, as it seems everything else is running fine, and especially since I've just replace the fan/capacitor. To replace the entire unit is about $4500, but they suggest that if I replace the entire unit, I should also replace the perfectly running furnace, since a new a/c unit uses the newer 'freon', and they like to match that with the furnace. I don't understand this. But, to replace both a/c and furnace is about $10,000. The a/c unit is about a 3.5 ton unit. I prefer to get by with the $2500 compressor, as I don't know how long I'll keep the house.

Any thoughts?

TIA

[CRNG]

On Tue, 2 Jun 2015 16:24:50 +0000 (UTC), Boris wrote in

Is the outside heat exchanger dirty or blocked up? Spraying water on it lowered the temp enough for the compressor to restart.

[Ralph Mowery]

It does sound as if the compressor is worn out after 18 years.

I don't understand why a furnace (you did not tell what type or kind) would have anything to do with the air conditioner. That statement abou tthe need because of the newer "freon" and a match seems bogus to me. I think I would be looking for a different company to do the work.

I believe I would replace the whole air conditioner. That way if it does not cool correctly it would be on the installer to make it right and he could not blame the problem on anything else.

[Boris]

CRNG wrote in news: [e-mail]:

Do you mean radiator looking cooling thing, that's visible when taking off a cabinet side panel? Yes, it was clean.

[Boris]

"Ralph Mowery" wrote in news:etydnXntsJtKQ [e-mail]:

The furnace is an American Standard, up-flow, housed in the hall closet. There are copper tubes (carrying what, I don't know, but they get cold when the a/c comes on)going to the furnace bonnet. I don't know the interaction, if any.

You're probably right.

Thanks.

[Terry Coombs]

Before you replace the unit , do as a couple of others have suggested and really clean the condenser coils - the radiator looking part of the outdoor unit . It can look clean and still have enough gunk on the fins to interfere with air flow and heat transfer . On the other hand , replacing a unit that old with a new more efficient one may be a good economic choice . Don't fall for that "we gotta replace the furnace too" crap . The systems are related in their handling of the air , but otherwise are independent systems .

[Boris]

"Terry Coombs" wrote in news:mkkpsr$ils$ [e-mail]:

Yes, thank you. I'm sure I can do that myself, as long as I'm careful and pay attention not to disturb any other components.

It can look clean and still have enough gunk on the

Does sound like crap to me, too. Especially since he couldn't give me a good answer as to why, no matter how many ways I asked for clarification.

I was also reading about cleaning the evaporative coil in the top of the furnace.

coils-part-3/

I doubt it's ever been done.

>

[Ralph Mowery]

I guess that the furnace is either gas or oil ?

The copper tubes that get cold are carring the 'freon'. If no one has explained how it works, here is a very quick explination. The compressor has a piston in it that compresses the gas to a liquid, then to the outside unit that air blows across it and takes away the heat. Then pipes it to the inside coils where the liquid goes through a small restriction in the pipe . There it absorbs heat from the air and causes the liquid to boil and turn into gas. This makes the coils feel cool.

Unless you have a heat pump that reversed the flow and the tubes inside get hot in the winter it has nothing to do whit the furnace, just uses the same blower and duct work.

I don't recall you saying what part of the country you are in. If in an area that does not get below 25 deg C very many days of the year, you may want to look at a heat pump. Cost should not be much more. If in a cold area of the country, then a heat pump will not be very efficent.

[Boris]

"Ralph Mowery" wrote in news:8fWdnW0DTv [e-mail]:

Gas.

Nope. that reversed the flow and the tubes

Yes, that's what I've surmised.

Sacramento, CA. high 90's to low 30's If in

[Ed Pawlowski]

Have the fins been properly cleaned? That would be my first step. They lose efficiency when cruded up. There is a cleaner made just for that purpose.

[Terry Coombs]

If you've kept up with filter changes it's probably pretty clean . Depending on how your system is put together it's probably a pure b***h to check .

[micky]

I like to match my date's lipstick with the color of my car, but it doesn't make the car run any better.

I don't know enough to comment on the compressor but as you know, the furnace doesn't use freon. It's just their way of trying to get you to spend more. Do techs get a commission when customers spend money? At least more money than a simple repair? Probably.

[Pat]

I agree with the others in saying that the furnace/air handler do not necessarily need to be replaced. However, don't confuse the furnace/air handler with the inside part of the air conditioner - the evaperator coil. Those are commonly replaced when a new outside unit is installed.

[Ralph Mowery]

I put in 25 deg C, should have been F. If it never got below 25 deg C you probably would never need heat..

You may want to look at a heat pump. It probably won't cost much more and may be less expensive to run than the gas for heat.

[Tony Hwang]

I wonder ODU fan is running reverse? Is the fan blowing out or sucking in the air? 3.5 ton for 1700 sq ft house? Mine is 2600 sq ft 2 story,

3 ton works just fine. 10,000.00 total cost for new system seems too high. If the compressor current draw is normal why does it OH? compressor in our unit is in a insulation jacket yet it never OH. Are the capacitors new for it? How about refrigerant oil?

[trader_4]

It's not exactly crap. You have an 18 year old furnace and an 18 year old AC. They both rely on the same blower and main controller board. When you're replacing the whole AC system, you're already at about 90% of the labor to replace the whole furnace. All that's left is to disconnect the gas line and the electric and chuck the old one out. Not many people are going to opt to replace most of an 18 year old system, but then leave and rely on the rest of the old equipment. And if they do it that way, then later the blower or the controller board fails, the installer has an unhappy customer. Eqpt cost, the furnace part is less than the cost of the AC part. And also if the furnace part needs to be replaced later, then you have more labor cost, because now you have to take apart the AC system again.

Your symptoms could be a dying compressor. IDK why it would cost $2500 to replace just a condenser. It sounds about 2X high to me. But I'm also not sure I'd put even that into an 18 year old AC system. The cost of $10K for a whole new system sounds several thousand too high to me. When I went out for quotes a few years ago, I was getting $7K - $9K for a 5 ton AC, 120K BTU furnace and that was in The Peoples Republic of NJ, which is one of the most expensive places. If you shop around, I'll bet you can do a lot better. Also, the fact that the tech had to call around, including the manufacturer to try to diagnose the problem, wouldn't leave me with so much confidence in them.

[J Burns]

I'd check the temperature of the tube taking the liquid freon out of the compressor unit with an infrared thermometer. The copper probably won't give you a good reading, but if you wrap it with electrical tape, you should be able to get a good IR reading from the tape.

If it's not much above the outdoor air temperature, the compressor radiator isn't the problem.

I'd be interested in the temperature between the compressor and the radiator. First, I'd google to try to find out what a reasonable temperature is.

On my compressor, I don't think I could get an IR reading with the compressor running. I'd tape the probe from an indoor-outdoor thermometer to the tube. (Actually, I'd use the probe that came with my multimeter because it's smaller.) I'd tape insulating material over it to keep air from cooling the probe.

If the freon going into the radiator is abnormally hot but it's good coming out, I'd suspect a restriction on the flow of freon somewhere in the system. I'm vague about air conditioning, but I believe there's a thermostatic valve on the evaporator. If it malfunctioned, I imagine that restriction could be severe enough to overheat your compressor.

[J Burns]

Come to think of it, I wouldn't bother to check the temperature of the tube coming out of the compressor. If the condenser is cooling properly and the compressor is too hot, I'd suspect a malfunction in a valve at the evaporator.

[Tony Hwang]

New furnace will have more efficient blower, probably VS or X13 type DC motor driven blower which is whole lot more efficient than old PSC type AC motor.

[J Burns]

How about your drier? Many times, a drier will last the life of the system, but not always. They can get clogged.

I've read that the water in freon can cause all kinds of problems. I wonder if one problem could be a buildup of ice in the valve on the evaporator that separates the high side from the low side.

When the compressor wasn't running, the ice would melt. Then the air conditioner would run normally until a buildup of ice blocked the valve. You'd lose your cooling, and I imagine the compressor would overheat.