Any thoughts why my furnace/air conditioner craps out in extreme temps?

[vi edit]

...other than it sucks?

Furnace/central air unit is just over 2 years old, as is the rest of the house. During extreme temps, (below 0 degrees, or over 90 degrees) the furnace fails to heat the house effectively and the AC fails to properly cool the house. It's just like the thing can't keep up. Right now it's about 95 outside and we have our thermostat set at 76 for the AC. Our house is 85 degrees and rising. We can hear the ac unit running, but no cold air is coming out of the vents.

Last winter when the house temp dropped below 60 degrees we swapped out the old mecury based thermostat for a new electronic one thinking that would fix the problem. Afraid not.

Is it a defective heating/cooling unit, or is it just too weak for what we need it to do?

 

[Gyrene]

I'd say you have a defective coil...unless the person who designed the central air system for your house is a moron, and didn't use a large enough unit. How big is your house, and what size unit do you have?

 

[Pepsi90919]

the problem obviously is that it sucks.

 

[308nato]

Weak or improperly set up. You may have insulation issues.

Iowa doesn't have enough corn cobs to stuff in your walls?

 

[Electric Amish]

It's either defective or you need a bigger one.

amish

 

[vi edit]

unless the person who designed the central air system for your house is a moron

I wouldn't rule that out

Model is a Lennox C23-26-1
Max design press is 450 psi.
Not at home so can't give you more info.

House footage is 1550 sq/ft in a split foyer townhouse.

 

[DT4K]

Have you cleaned the filters?

Clogged filters can lead to reduced air flow, which can cause problems. If it's hot enough out that it's running constantly, the reduced airflow can lead to condensation on the coils. This condensation can then freeze and block even more airflow. Which basically makes it useless.

Or it could just be too small for the house size, or it could be defective.

 

[T3C]

Originally posted by: dtyn
I'd say you have a defective coil...unless the person who designed the central air system for your house is a moron, and didn't use a large enough unit. How big is your house, and what size unit do you have?

 

[vi edit]

Clogged filters can lead to reduced air flow, which can cause problems. If it's hot enough out that it's running constantly, the reduced airflow can lead to condensation on the coils. This condensation can then freeze and block even more airflow. Which basically makes it useless.

I shop vac out the filter every couple months. Should probably do that again.

 

[Gyrene]

Ok, I just ran a really quick down and dirty load. I don't have the information (location, number of rooms, appliances, windows sizings, etc.) to do a real accurate load. However, from the squarefootage and current unit, I determined that your unit is about 1/2 of what you need. Your unit has a max capacity of 23 MBh, you need about 45 MBh. Meaning approx. a 5 ton unit to be perfectly comfortable.

Of course, that was down and dirty. If, when you get home, you can give me the exact tonnage of your unit, appliances you have, etc. I can run a much more accurate load. But to be honest with you, I think it will just come up worse than what I ran. From what I can tell, you need about a 5 ton unit.

 

[Lounatik]

dtyn,
5 tons for a 1550 sq ft house? That seems awfully high, I would have figured maybe 3 tons max.When I lived in Fla and did ac work for a living , I thought it was 1-1.5 tons per 1000 sq ft. Hell, it may have changed over the years. I bet that the problem he could be having is the overload on the compressor is cutting out early and the condenser fan is still running , but the compressor isnt. If it gets hot enough the damn overload wont kick back in for a good while. Another problem could very well be the design of the house: split foyer homes tend to be cool on one level and hot as hell on the other. I know, I live in one.

vi_edit, you said you changed out the thermostat , did you check to make sure the wires were connected properly? That could be a problem.

One more thing: vi you say that you shop vac the dirt out of your filter. Do me a favor and try to get the filter cleaned by a pressure cleaner(like at a self serve car wash) blast the filter front and rear, because I dont think that the shop vac is an effective way of cleaning it. And one last thing try to find out if your air handler(In the house) has more than one filter in it . You never know how devious these companies are ;>)



Peace


Lounatik

 

[vi edit]

Lounatik,

You are absolutely correct on the split foyer - the downstairs is frigid, and the upstairs is a friggin sauna. To help that out a bit, we close most of the vents off downstairs. Keeps temps a bit more consistent.

I will probably just buy a new filter. Sounds easier than getting it pressure cleaned. I'm pretty sure we got the new thermostat hooked up properly. It's only in extreme temperatures where it fails to work properly. It really seems to get fussy when we have huge changes in temps in a short amount of time. Like going from 60 degrees to 95 degrees, or going from 40 degrees to -20 degrees in a days time. It just overwhelms it and it doesn't seem to be able to catch up.

 

[Lounatik]

vi_edit,

I hear your pain man! Go to a self serve car wash place and spend a 1.50 and clean the thing. If you want to get a decent filter go to Lowes or Home Depot and get an electrostatic air filter. They trap a significant amount more dirt than conventional filters plus they are reuseable . They cost about 30.00, and are well worth it, IMO.

What I did to combat the constant running ac was to get some fans put into my attic.One at each end of the house. They are thermostatically controlled, and you have to run wiring to them. But the benefit I get is the heat load is taken out of the place where it likes to live: Up high near the thermostat in my hallway. The fans run until about 10 pm in the summer and not at all come fall.

Your builder more than likely installed the bare minimum ac for your house. So nice and cheap for him and sucks for you.




Peace


Lounatik

 

[Gyrene]

Originally posted by: Lounatik
dtyn, 5 tons for a 1550 sq ft house? That seems awfully high, I would have figured maybe 3 tons max.When I lived in Fla and did ac work for a living , I thought it was 1-1.5 tons per 1000 sq ft. Hell, it may have changed over the years. I bet that the problem he could be having is the overload on the compressor is cutting out early and the condenser fan is still running , but the compressor isnt. If it gets hot enough the damn overload wont kick back in for a good while. Another problem could very well be the design of the house: split foyer homes tend to be cool on one level and hot as hell on the other. I know, I live in one. vi_edit, you said you changed out the thermostat , did you check to make sure the wires were connected properly? That could be a problem. One more thing: vi you say that you shop vac the dirt out of your filter. Do me a favor and try to get the filter cleaned by a pressure cleaner(like at a self serve car wash) blast the filter front and rear, because I dont think that the shop vac is an effective way of cleaning it. And one last thing try to find out if your air handler(In the house) has more than one filter in it . You never know how devious these companies are ;>) Peace Lounatik

I told you, it was a down and dirty load. You have to factor in glass, appliances, people, attic space, building orientation. I design systems for a living, currently, and yes 5 tons seems like alot for 1550 sq ft, but you have consider what's in that space. I'm assuming refridgerators, open ovens, microwaves. Hell, a refrigerator makes about 1500 btus on its own. We don't have set tonnage per sq ft, you have a minimum cfm per ton, and 1500 cfm should be what's required to cool that house properly.

EDIT: You're right, I used design specs for an OB, which is much heavier in Misc loads then Residential. A 3 ton unit should suit your needs perfectly, given it has the correct MBh rating.

 

[Ime]

By tonnage, are you talking about how heavy the A/C unit is?

I know nothing about A/C units but 5 a ton unit seems huge!

 

[Electric Amish]

Originally posted by: Ime
By tonnage, are you talking about how heavy the A/C unit is?

I know nothing about A/C units but 5 a ton unit seems huge!

Tonnage in A/C does not refer to weight. It has something to do with the capacity to cool/heat the air of a unit. Larger = more capacity.

amish

 

[Gyrene]

Originally posted by: Ime
By tonnage, are you talking about how heavy the A/C unit is? I know nothing about A/C units but 5 a ton unit seems huge!

1 ton = 12,000 Btu/h. I believe it was derived by how much heat it took to melt a 1 ton block of ice in an hour.

 

[Pepsi90919]

i still say it sucks.

 

[OZEE]

5 tons should cool about 3000 SqFt. So for his 1550 SqFt he'd need something like 2.5-3 Tons... of course, depending on insulation.

Originally posted by: Ime
By tonnage, are you talking about how heavy the A/C unit is?

I know nothing about A/C units but 5 a ton unit seems huge!

 

Insulation or or it's not powerful enough for your space.

Usually its a combonation of both.

 

[Eli]

Originally posted by: dtyn

Originally posted by: Ime
By tonnage, are you talking about how heavy the A/C unit is? I know nothing about A/C units but 5 a ton unit seems huge!

1 ton = 12,000 Btu/h. I believe it was derived by how much heat it took to melt a 1 ton block of ice in an hour.

LOL.....

That's almost as bad and archaic as the horsepower rating.

 

[cavemanmoron]

my Dad has central air,and a 2 story ranch,it is always cooler downstairs,
i think they should split the houses into 2 zones,1 for each level,
a seperate unit for each floor,just as if it was a 2 family house.

insulation,windows,etc have an effect.
Attic,venting helps..

hot air heat is the sux very inefficent,imho.

 

[arcas]

Hmm. I have a 2400 sq ft house with 2 2-ton Carrier units and on hot days the upstairs rarely falls below 80 deg even with the upstairs AC running (new compressor was installed last summer before I moved in). It's a very open floorplan with vaults and cathedral ceilings so the upstairs collects alot of warm air.