Quick question on Home A/C

[Snaggletooth]

We had a hot spell here last week and had the old A/C running during the 100 degree temps for a couple days. Thursday night I woke up and it was 85 in the upstairs rooms. Checked the vents and was getting only warm air and didn't feel like much flow. Checked the thermostat and it was set for 70 but the room temp was showing 80.

 

I shut it down and figured I'd call the maintanace guy in the morning.

 

I got ahold of him and told him the problem. Ok, be a few days. Great. Frinday night I decided to try my luck and kicked it back on. Got some cold air, shut down all the lower vents and I was able to get the upstairs bedroom cooled down enough to sleep. By morning it was doing the same thing. Shut it down again.

 

Saturday night I tried the same thing. Got me though the night and back to hot in the AM.

 

So from what little I know I assume the coils are freezing over while running and thawing out when I shut it down. The unit is on the roof of the two story town house so I can't get to the unit to look it over.

 

I fired it up a few hours ago and I'm already getting warm air.

 

So I'm going to be having a talk in the morning with the guy. I'm not going to be too judgemental but I know the help here can be a little ....lacking.... at times.

 

What would be the common cause for this? Low Freon? Compressor failure?

 

I'm just trying to learn what I can so I don't get a run around from the guy.

 

Going to be a muggy night

 

Thanks

 

Mike

[Wade 2000]

Sounds like your unit is freezing up. That's why it works for a bit then quits circulating. This is usually a coolant pressure problem.

[Guest tx2sturgis]

Sounds like it could be low on freon, (or whatever refrigerant it uses).

 

Setting the thermostat for say, 75, or 80, it might work enough to keep things livable, without freezing up.

 

It COULD be that the condensor coil outside, or the evaporator coil inside, is dirty or blocked, or maybe, just maybe, its a simple matter of changing the airfilter in the airhandler inside. If they get severely dirty, the evap coil will freeze up and...then things dont work very well.

 

Check the filter first.

 

 

 

 

 

 

 

[Snaggletooth]

Sounds like it could be low on freon, (or whatever refrigerant it uses).

 

Setting the thermostat for say, 75, or 80, it might work enough to keep things livable, without freezing up.

 

It COULD be that the condensor coil outside, or the evaporator coil inside, is dirty or blocked, or maybe, just maybe, its a simple matter of changing the airfilter in the airhandler inside. If they get severely dirty, the evap coil will freeze up and...then things dont work very well.

 

Check the filter first.

 

Got that covered. I change mine every month. ( just checked, swapped it out anyway) Furnace unit was replaced two years ago and increased air flow a huge amount on the second floor, not to mention the operating costs dropped about 30%.

 

This place was built in 1972 with a flat roof. In Nebraska! Go figure. That adds a bunch of heat to the second floor. 4 years ago they redid the roof with the white rubber membrane and that helped a lot with reflecting the heat off.

 

I'll try a higer setting tonight to.

 

Thanks

 

Mike

[uncledj]

The two most likely causes of evaporator (inside coil) freezing will be that it's low on refrigerant or that there's a lack of airflow due to a clogged filter, or matted dirt on inlet side of evaporator coil.

I'd bet that it's low on refrigerant, which will beg the question...Where did the refrigerant go????

The guy who looks at it will probably charge it up and it'll be ok for a while, but this problem will come up again in the future.

Depending on the age, it may be an R22 or a R410a system. If it's R22, you'll want them to make some effort to find and repair any leaks, as R22 is becoming quite expensive.

If it's R410a, the refrigerant will be 1/3 of the cost, but any leaks still should be found and repaired.

Finding and repairing leaks can be a pita, so the tech will probably try to get out of it if he / she can. You may have to push a bit, but if you're paying for their time....time is money.

Keep in mind that as it loses refrigerant, it'll loose cooling capacity, and without enough refrigerant, the compressor loses it's cooling, up until the system loses enough gas to freeze up the evaporator, then with the lack of airflow, liquid refrigerant can / will return to compressor. Plenty of compressor cooling then,....but very unhealthy for compressor. Liquid refrigerant will foam the oil as it boils out, and oil foam doesn't lubricate adequately,....and should liquid refrigerant get to the head it'll be lights out for the compressor. Liquid doesn't compress so well.

 

Point being....when these systems are properly charged and maintained they'll run practically forever. When they're allowed to suffer abuse, they die pretty quickly.

 

Sorry for the rambling. I've been doing this for over 25 years now, and the post struck a chord.

Hope this helps.

[Snaggletooth]

Thanks for the info guys. They sent a repair guy today and it was a different one than usually works here. I'm told he isn't with the company any more. Wonder why?

 

But he found a leak on a valve at the condensor, resealed it and filled the system back up. Rechecked everything and found no other problems.

 

Back to chilly! Of course it's been in the 60's all morning and a nice breeze blowing. Looks like I won't be needing it for a week or so now.

 

Life is cool.... and not so sweaty.

[MiCarl]

Since the original problem is solved I'm going to hijack the thread:

 

I just installed a 3 ton split system in my shop over the weekend. The guy who did it is a retired HVAC tech with no R410A experience.

 

This system is running at 330PSI on the liquid line and about 80 on the vapor line at an ambient temp of 75 degrees. I'm having some trouble with the evaporator coil icing.

 

It looks to me like the liquid line should be at about 280PSI and the vapor line at 140 (ambient air 75 degrees). I'm thinking the equipment supplier must have put the wrong orifice in the evaporator. The equipment supplier is telling my friend that the problem is we don't have enough airflow, but the blower is on max speed and we have no duct work, just a filter.

 

Any thoughts?

[Prairiehammer]

Carl, I posted your question on another forum, that is frequented by a Professional HVAC contractor/owner.

 

I'll keep you posted with his comments.

[MiCarl]

Carl, I posted your question on another forum, that is frequented by a Professional HVAC contractor/owner.

 

I'll keep you posted with his comments.

 

Thanks!

[uncledj]

Still getting used to the new 410a, but it looks to me like you should be running a bit over 100 suction (vapor) pressure with 15+ degrees superheat.

Liquid pressure at 330 should be good.

I'd ask what the temp of the liquid line is.

On a 75 degree day it should be lukewarm, or even a bit cooler.

The suction line should be nice and cool,...cool enough to sweat but not ice cold.

If superheat and subcooling mean anything to you, you should try to get around 15 degrees superheat and around 10 degrees subcooling.

Those numbers should be pretty close, but I'd have to research to give you textbook numbers.

Suction and liquid line temperatures are just as important as pressures.

Incorrect orifice would be a cause of low suction / freezing, so would lack of airflow. Other things to consider are a partially plugged orifice or liquid line filter, or if it has a TXV as a metering device it may need adjusted.

 

I would also want to know the temperature drop across the evaporator and the condenser. It could just need a bit more of the ol' freezone.

 

As far as you friend not being familiar with R410, I've found that it's got pretty much the same characteristics as R22, but just runs higher pressures. Many of the new blends have a wide temperature / pressure "glide" which makes charging a challenge, but R410 really doesn't have that problem.

 

I got edjumicated and certified for R410 a couple of years ago, but mostly forgot what I learned in the books, and rely on experience to get me by.

Every now and again I do have to refer to the charts though.

Best of luck.

Let us know what happens.

[MiCarl]

There is a lot of terminology I'm not familiar with. I do understand the basic principles of how the system works.

 

Everything is brand spanking new. The blower was set at 1200CFM (maximum setting) with no duct work at all. There are filter tracks in the cabinet and a filter is installed there. That puts us at 400CFM/ton which falls right in the mid point of the manufacturer spec. I've since moved the jumper to add 10% to the blower output, so I should now be at 1320CFM.

 

It has a fixed orifice. If I understand correctly that is not a TXV.

 

One thing my friend did is use a bit of the refrigerant to flush the lines. I'm wondering if the R410A might be more sensitive to that loss than R22, or perhaps he's used to systems that have a factory charge for a long line set. This unit specifies that it came charged for a 15' line set, which is about what we have.

 

He's panicking about the high liquid pressure, but things I'm finding on the web indicate it often runs closer to 400PSI.

 

The liquid line is luke warm at most. I was surprised because I remember the old automotive R12 systems being uncomfortably hot.

 

The suction line is insulated pretty much end to end so really can't feel it. There is about 1/2 inch exposed at the air handler and I haven't noticed any condensation. It did eventually show frost, which is what made me check the evaporator coil.

 

I don't have the correct tools to measure all the temperatures and air flows. Not sure whether my friend does or not, but he gets prickly about my questions/suggestions.

 

I've about convinced myself it needs a little squirt of refrigerant.

[Gunfighter]

The fact that he used some of the refrigerant to "flush" the lines bothers me a bit. Any refrigeration system should be put under a deep vacuum to remove all non-condensable gases (air) and all water vapor. 410 is EXTREMELY intolerant of any of the above contaminants and the oil used in these systems is very hygroscopic (absorbs moisture). If the system was not put under a deep vacuum (under 500 microns) the refrigerant will have to be reclaimed and recycled, the system vacuumed, and new refrigerant installed.

If there are any contaminants left in there, the orifice may well be freezing up and restricting the refrigerant flow. Any non condensable gases will give you a low suction pressure and possibly high head pressures also.

When putting the system under vacuum one CANNOT go by the low pressure gauge on the manifold set, one MUST use an electronic gauge made for that purpose!

"Flushing" the line set and the evap went out the window years ago, for one thing they are mostly pressurized with nitrogen from the factory and that will just mix with the refrigerant while flushing and give you problems. It also loses some of the refrigerant and these systems are critical of the charge level. Also, not putting the system under the recommended vacuum for the recommended time may throw the warranty out of the window.

Hope this helps.

[Prairiehammer]

Carl,

Just to muddle your noggin some more (it certainly swooshed over my head), here is Greg Snyder's response to your inguiry:

 

For a 75 degree ambient the high pressure should be around the 300 to 320 range and the suction pressure has to be above 102lbs or so to keep the evaporator temperature above 32 degrees but 120 is a more likely pressure if the airflow is sufficient. Have him check the superheat, that should indicate whether the problem is an underloaded evaporator or a starving evaporator. If it is underloaded your superheat will likely be below 10 degrees but if it is starving it will be around 40 degrees. The system should have an expansion valve unless it is a real low grade builders model, but airflow could be the problem if you have no duct work attached at either end. A blower wheel without any static pressure will overload the motor and slow the rpm's to the point that it doesn't move enough air. Usually the motor will trip out on the overload in a short period of time if this is the case, but comparing the actual amperage draw to the design draw shown on the motor should give you an indication of motor loading. It could also be an airflow or refrigerant restriction also.

Edited May 21, 2013 by Prairiehammer

[MiCarl]

To be clear: He pulled it down to 300 microns over night. Released some refrigerant into it and pulled it down again.

 

It probably is a low grade builders model. I went cheap: Ducane.

[Guest tx2sturgis]

Add a half bottle of Seafoam. Call us in the morning.

 

 

[Gunfighter]

To be clear: He pulled it down to 300 microns over night. Released some refrigerant into it and pulled it down again.

 

It probably is a low grade builders model. I went cheap: Ducane.

 

 

300 micron overnight should have been sufficient. Most likely lost enough during the "flushing" to be low on charge. The previously posted pressures are pretty close depending on the ambient temperatures and if all else is correct just bring the charge up until the proper superheat has been met and it should be OK.

 

Yes, the Ducane will be about as cheap as you can get.

[MiCarl]

Yes, the Ducane will be about as cheap as you can get.

 

Since I rent I didn't want to sink a whole bunch into infrastructure. There was already 30 amps to the roof from an old mini-split and I didn't want to upgrade the electric. That pretty much capped me at 3 tons which should be marginal for the space. The goal was to have it just dump some cool air in the area where I do most of my work.

 

Yesterday afternoon it was 93 degrees and humid. Even with the icing it kept the whole space at a comfortable 75 degrees. It's also whisper quiet.

[Guest]

Since Mike found out his problem ill just toss something in here that will also create an icing condition that some may not be aware of. I had icing from time to time on my 3.5 ton Trane maybe a year after it was installed (2001). Turns out the drain lines get clogged with slime and causes the icing. So, after sucking my lines dry with a shop vac I now take 2 cups of bleach or chlorine and dump it into my drain line twice a year. Keeps things going smooth now. My unit is upstairs so I have a long line to clear. So far so good.

[Flyinfool]

Since Mike found out his problem ill just toss something in here that will also create an icing condition that some may not be aware of. I had icing from time to time on my 3.5 ton Trane maybe a year after it was installed (2001). Turns out the drain lines get clogged with slime and causes the icing. So, after sucking my lines dry with a shop vac I now take 2 cups of bleach or chlorine and dump it into my drain line twice a year. Keeps things going smooth now. My unit is upstairs so I have a long line to clear. So far so good.

 

Be careful with bleach.

Bleach will dissolve stainless steel whether it be fasteners, pipe fittings or sheet metal.

[pmelah]

where do i put the seafoam in at :rotf: i had a problem with my air handler freezing after running for an hour or so did this 3 times one nightnext day i sprayed purple power on it and the outside unit hosed it down kept it off for a week and then turned it back on and havent had a problem since that was 3 days ago nice and cool inn here now

[MiCarl]

Ok the major problem has been identified:

 

The guy who did the inside low voltage wiring (me) overlooked the connection that lets the air handler know the thermostat is calling for cooling. It was running at the speed for when the thermostat calls for blower only - 600 CFM. So we only had half the airflow we were expecting. Those of you that said airflow were correct.

 

It's not as quiet as it was, but the icing problem is eliminated.

 

Tomorrow we'll double check the numbers and see if we need any refrigerant.

 

Thanks everyone for the input.

[Guest]

Be careful with bleach.

Bleach will dissolve stainless steel whether it be fasteners, pipe fittings or sheet metal.

 

Its all PVC lines. I never put bleach into the A/C itself, just the drain lines which are all PVC. Should have clarified that first.