Central Air Conditioning: Problems

[StarsFan4Life]

So last April, my wife and I purchased a new home. The AC unit that came with the house was an oversized (for the house) Carrier product. Back in April of this year, we had to have the compressor replaced due to horrible noise.

Yesterday, the outside unit was not cooling the house well at all. My wife had turned it down to 76 from 79-80. It stayed 79-80 for about 3-4 hours without ever cooling the house down. Our home is WELL insulated and never have trouble getting the house to cool, usually takes about 30 minutes if not less. Granted it was a little humid and around 100 here in Texas yesterday, but it still would cool the house down just fine before.

I went out to check on the outside unit and came outside to a horrible high pitch noise coming from the unit. I immediately turned the unit off. I turned it back on a few minutes later and it did the same thing. I sprayed the coils off with cool water and the noise went away, but as soon as it dried up, the noise came back.

I am still under a 2 year warranty and am having the builders AC repair company come out and "fix it" once again, but I am afraid they will try to replace the compressor again for another REFURBISHED unit like I know they did before.

Going in to this meeting with the AC repairman, what should I know (as the cause of the problem) and what should I ask him to fix?

 

[Anubis]

ask for a brand new unit

 

[Newbian]

Make sure a mouse isn't plugging it up.

 

[StarsFan4Life]

Make sure a mouse isn't plugging it up.

Where in the world would a mouse plug it up at?

 

[Newbian]

Where in the world would a mouse plug it up at?

One can never know because they can pop out of it in so many places.

 

[krose]

Do you notice any ice forming on the evaporator coils? When mine did that the refrigerant was leaking. Have them check the refrigerant to see if it needs more. Unfortunately diagnosing the leak can be costly, I ended up getting a modern unit that cools better and is more efficient.

 

[vi edit]

Do you notice any ice forming on the evaporator coils? When mine did that the refrigerant was leaking. Have them check the refrigerant to see if it needs more. Unfortunately diagnosing the leak can be costly, I ended up getting a modern unit that cools better and is more efficient.

I had that exact same problem. It was running, but the temp just kept going up in the house. Went outside and looked and the supply line to the house was a block of ice. It was a refridgerant leak in my case too.

 

[StarsFan4Life]

Do you notice any ice forming on the evaporator coils? When mine did that the refrigerant was leaking. Have them check the refrigerant to see if it needs more. Unfortunately diagnosing the leak can be costly, I ended up getting a modern unit that cools better and is more efficient.

It will not cost me a penny....it's still under warranty with the home builder, which is why I want to get everything fixed now.

 

[Lounatik]

Was the outside fan still running at high speed or slowly turning? A high pitched noise MAY indicate bad bearings in the fan motor or bad start capacitor. Also a high keen may be the compressor trying to restart too soon due to possibly a bad capacitor or a weak overload protector inside the compressor. Though that noise would be a lower pitched hum more than anything else.


Peace

Lounatik

 

[bobdole369]

A high pitched whine could also be a bad bearing in the compressor motor, or also a pinhole leak in the condensor coils.

Is the air coming through the fan that cools the condensor coils at all hot? I would think with a pinhole leak the condensor would be the opposite of hot. Also I would imagine any leak wouldn't stay around for long.

In any event, the HVAC dude should be able to fix it.

 

[PottedMeat]

Texas? Longshot, but check for fire ants committing suicide in the relay contacts.

 

[Crusty]

Texas? Longshot, but check for fire ants committing suicide in the relay contacts.

haha, I knew fire ants were little shitheads but this one is new to me.

 

[Rubycon]

Compressor replacement is major work and if not done correctly particularly CORRECT evacuation to remove moisture from system the new compressor will likely fail. Especially if the prior compressor suffered a burnout. Severe burnouts make the oil highly acidic and there are procedures to be followed SPECIFICALLY to deal with this. If it's done half-ass and with hurry the new compressor will have a greatly shortened lifetime.

Squeal can be caused by excessive head pressure. The common culprits are clogged condenser coils, recirculation and a condenser fan motor failure. If this fan is turning at normal speed check the temperature of the small (liquid) line. It's ok for it to be warm but not HOT to the touch! When this line is hot or too hot to touch then your head pressure is too high. If the high pressure cutout fails and the head pressure continues to rise it's truly scary how high it can go and the compressor will get louder as it works harder and can make unusual noises of mechanical strain. With increased work means an increase in run winding (single phase CSR) current and temperature. An overcurrent (Klixxon) SHOULD open under these conditions but they can arc closed too. The compressor (trades folks call 'em tin cans for smaller residential ac units) can get really hot too. In a properly operating system it should be cooler on the suction side where the larger pipe comes in and warm to fairly hot on the discharge side where the hot gas leaves. If the entire can is hot to touch it's not operating correctly.

A restriction in the liquid line (if there is a filter drier which SHOULD be installed after a burnout!) can cause issues as well. As a filter drier gets plugged up it starts to restrict the flow and with pressure differential comes with temperature differential as it will start acting like a metering device of its own which is NEVER good. Severely clogged filter driers will actually frost up on the exit side! If this is ever observed the system needs immediate servicing to remove/replace the filter drier.

A GOOD tech will take care of this and a PROPER compressor changeout (particularly if a severe burnout is involved) is not to be taken lightly. Done properly the unit and new compressor should last for years and far beyond any normal warranty period.

 

[StarsFan4Life]

The problem ended up being pretty simple to diagnose, but a little tougher to fix. The HVAC came out and ran some line tests. First things first was the PSI. Normally my unit should sit between 325-350, but it was well over 500 (close to 550), The was causing a release valve in the compressor to by pass the refrigerent and basically just "run" the unit without evectively cooling anything. After looking at the previous paperwork, the last HVAC put in 10lbs of refrigerent after replacing the compressor and capactior (and filter drier), but the unit apparently only calls for 7.25lbs. This could have really caused some serious issues, and dangerous for that matter.

The guy today bleed the system a bit and got the numbers down, but didn't like where the cooling/releasing numbers. He is ordering a new valve (something in the main unit in the addict) and will be coming out to bleed the whole system, run nitrogen through the line coils and remove whatever might be in there.

Noise is gone and the house is cooling, just a little more to go!

 

[Sea Moose]

The guy bled the system? LOLOLOLOL

He needs to WEIGH out the gas charge. This is the only way to be sure the system has been charged correctly. NEGLIGENT TECHS CHARGE SYSTEMS OFF PRESSURE, GOOD TECHS CHARGE OFF WEIGHT AND MEASURE THE PIPE RUN.


Did i make myself clear?

Btw i am a hvac tech and rubicon is someone to listen to. get the tech to also do a vacuum test on the compressor and check how many amps its drawing. Sounds to me like the warranty techs did a poor job.

Also, bleeding refrigerant to atmosphere is ILLEGAL. HE should be using a recovery unit.

 

[Sea Moose]

oh and for the love of god can you people start using the metric system?

Psi!!!??? Fahrenheit???


Damn you Merrycans!

 

[Rubycon]

Yes overcharging will result in high head pressure. It can also damage the compressor when the system is operated in lower ambients due to excessive liquid flowing back to the compressor. Heat pumps are more tolerant of this because they have a suction line accumulator to hold extra liquid however if it becomes full the excess liquid will flow into the compressor's suction line. These are positive displacement compressors and intolerant of liquid entry so they will get damaged if slugged. That unit should have NEVER been running with a head pressure that high! Do residential units no longer have high head pressure cut out switches?

The system COULD be restored closer to ideal charge by removing excessive refrigerant while monitoring head/suction pressures, condenser/evaporator differential temperatures and calculating what's known as superheat. No need to evacuate out and weigh the charge back in. (Weighing OUT may tell you how much has been removed but the amount remaining still is not precisely known. This is why they still have no idea how much oil is spewing out of that well but if they collected 25k barrel in a day and the video shows a lot leaking common sense tells one that's a lot more than what they said! A good tech knows by using the superheat method.

Also Moosey keep your pantyhose on! Using Imperial measurements is fine. It becomes a PIA to go between one and the other but still something anyone proficient in fifth grade math can do in their head.

 

[LTC8K6]

the main unit in the addict

What an odd A/C system. What is the addict addicted to, and does he live in your attic?

 

[Rubycon]

What an odd A/C system. What is the addict addicted to, and does he live in your attic?

Attic systems fight back when neglected. Their pee traps get slimy so they just pee all over the place staining your ceiling and inviting mold spores.