# costs for AC compressor unit



## saichele (Jun 18, 2007)

I noticed the manufacture date on my AC compressor is 07/83, but it's still working.  I have a rough idea how much it costs me to run the AC, but I'm curious how much I'd be looking at for a new compressor installed.  The house is about 2500 sf ith decent insulation but shabby ductwork.  
Summer highs seldom go above the low 90's, but dewpoints push 70 pretty often.  

Thanks
Steve


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## begreen (Jun 18, 2007)

Is this central air Steve? Are you talking about just replacing the existing compressor with a new one or replacing the outdoor condensor unit entirely? You'll benefit more by replacing it with a new high efficiency unit. There has been a lot of work done in this area in the past 25 years. How many tons is your unit? I'm doing an out of the hat guess at 4 tons.  I'm guessing you'll need a new coil due to refrigerant differences. If that's the case, I'd guestimate $3500 for a high-efficiency condensor unit and coil replacement.


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## saichele (Jun 18, 2007)

Central AC, frankly I can;t make anything out of the tag on it even.  Some of it is illegible, but nothing that looks like BTU, tons, SEER, any of the terms I'm used to.  

I was actually thinking of doing the whole outdoor unit, but somewhat hopeful it could be as straight forward as just plumbing and wiring the new unit.

Steve


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## Sandor (Jun 18, 2007)

Steve, please put your city and state in your profile so everyone can see your location. It makes sense for posts like this.

That being said, this is the worst time to shop A/C work... the start of summer. Here in Virginia, the temps are going to be low-mid 90's for the next couple of days and I'm sure all of the contractors are busy.

Shabby ductwork will obviously hurt. Also, if you don't replace the inside unit, be sure to take it apart and give the coils a good cleaning.

New units are way more efficient than units made 20 plus years ago, like BeGreen said.

Important Point! An over sized unit is WAY worse than an undersized unit in a climate where dehumidification is important. And by the look of the dew point you provided, you need to get rid of humidity. If you can't hold the indoor humidity level of at least 55 percent or less, then you may be over sized.

From all of the playing around I have done, small Energy Star window units cannot be beat. No ductwork loss. Easy to take out in the fall and give it a good cleaning. Cheap to run. Cheap to buy. They do a really good job of dehumidifying, just set the temp at like 72 and let it run. And you can zone-cool.

Finally, any cost analysis you do, take your cost for electricity now and double it. You can see that your older unit lasted over 20 years, and I think 10 to 20 years from now, electric will be at least double from what you are paying now. Good Luck!


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## jjbaer (Jun 18, 2007)

Sandor said:
			
		

> Finally, any cost analysis you do, take your cost for electricity now and double it. You can see that your older unit lasted over 20 years, and I think 10 to 20 years from now, electric will be at least double from what you are paying now. Good Luck!



But.....even at double todays electric rates, your electric bill may not be that much higher than it is today because of the greatly increased efficiency unit you'll be replacing your 25 year old unit with.......put another way:  you spend "X" now on electricity for A/C.  Replace that 25 year old unit, today, with a new SEER 16 or higher unit and your electric cost for A/C will PLUMMET IMMEDIATELY........so.....even with increasing electric bills, it will be MANY MANY years before your electric bill for A/C matches what it is today with your old unit......


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## TMonter (Jun 18, 2007)

I'm with Sandor, window units are the way to go in most cases unless you simply don't want the hassle of changing them out every year and the nice thing is they zone cool effectively without cooling areas you don't need and don't have all the ducting losses.

My guess is that with the ducting losses included, a window unit is more efficient overall than a central air unit.


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## begreen (Jun 18, 2007)

Window units can be a decent substitute in some houses. Be sure that the circuit is generously adequate for the load and if at all possible dedicated to the window unit. This is especially true for big 220v units.


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## saichele (Jun 18, 2007)

We have one window unit, I think the main thing that bothers me about it is the aesthetics of having AC units hanging out the windows.  And I'm not exactly flush with windows, particularly on the larger spaces.  I could certainly air condition the whole house with about $500 worth of AC units.  But it might be worth an additional 500 to not have to dink with it.


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## BrotherBart (Jun 18, 2007)

Steve said:
			
		

> We have one window unit, I think the main thing that bothers me about it is the aesthetics of having AC units hanging out the windows.  And I'm not exactly flush with windows, particularly on the larger spaces.  I could certainly air condition the whole house with about $500 worth of AC units.  But it might be worth an additional 500 to not have to dink with it.



I agree on the looks thing. That it why the two upstairs window units and the one down stairs in the kitchen window are all in the back of the house. The squirrels in the woods back there haven't laughed that I have heard. Can't argue with only an 80 buck increase in the electric bill in the hottest three months of the summer of 90 degree and up days and 70 - 90 percent humidity with 2,500 sq. ft. to cool. Three hundred bucks for all three including remote controls. Still trying to figure out why the heck they need remotes but they came with the units. Gonna hold off on paying five to seven grand to replace the dead heat pump for a few years.

Wish I could buy enough firewood at $80 a month to heat the place. And only have to pay $300 for stoves and pipe!


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## Sandor (Jun 18, 2007)

castiron said:
			
		

> Sandor said:
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Cast, that is one lame ass post.


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## Sandor (Jun 18, 2007)

Steve said:
			
		

> We have one window unit, I think the main thing that bothers me about it is the aesthetics of having AC units hanging out the windows.  And I'm not exactly flush with windows, particularly on the larger spaces.  I could certainly air condition the whole house with about $500 worth of AC units.  But it might be worth an additional 500 to not have to dink with it.



....and only you can decide whether its worth dinking with or not.

I have seen enough skunky condenser units with loads of green snotty looking crap in the condensing pan to make you puke.

So, I will take the "dink" factor and yank out the ugly window shaker in the fall to give it a good cleaning.... knowing I am not breathing all of the chit thats growing in the pan, year after year.

If you have flexible ductwork, you may want to check for mice. They love it.


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## jjbaer (Jun 19, 2007)

Sandor said:
			
		

> castiron said:
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> ...


 
Sandor,

what load of s%$t are you trying to foist on people.????......sure electric MAY be double in 10 years...then again, it may NOT...the point is however, that the increased efficiency of a new unit vs one 25 yrs old  will most likely result in electric bills being BELOW todays bill even 10 years from now.....if you have a problem with the logic, then say so...otherwise don't bullsh&t around with crap like "that's a lame ass excuse"........


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## Sandor (Jun 19, 2007)

castiron said:
			
		

> the increased efficiency of a new unit vs one 25 yrs old  will most likely result in electric bills being BELOW todays bill even 10 years from now.....if you have a problem with the logic, then say so..



Ok, I have a problem with that logic.

I strongly believe that the cost of energy, in every form, will be substantially higher 10 years from now than it is today.

If you believe otherwise, which your post suggests, then you are getting your "information" from Fox News and CNBC.

I suggest you read theoildrum.com every day. Start out with the daily "Drumbeat" section that outlines the top energy news from around the world. Research the provided links and educate yourself. This stuff is simply not covered on MSM, which exists as a profit center to sell ad space by the minute. And people are not in a buying mood if the news is bad!

So, if you think that electricity will still be cheap 10 years from now, I think that you really do not understand the magnitude of the problems that this (and many other countries) are facing.

Sorry for the hack on ya Cast, but making statements like the above implies ignorance about what the real issues are involving energy in the future.


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## Rhone (Jun 19, 2007)

I always wondered why they don't make smarter AC units.  Ones that detect what the outside temp & humidity is and adjust the "vent" accordingly.  I always thought a great idea would be one that's smart enough to recycle the inside air during the day when it's 80F+ outside and then automatically detects if the outside air is less than the house air (at night) it should open the vent and use outside air instead.  Maybe even detect if the outside air is much colder shut off the compressor all together and just turn into a window fan so to speak.  That would work well for those hot days and cold nights.  

For outside units, why don't people make water cooled units?  Something like a ground source heat pump at a more simple level.  It's not usually hard to bury some stretches of PEX tubing and link it into outside units.  Water is much better than air at transferring energy so the outside unit could be small, and more efficient especially at noon using the ground instead of air to cool when it's needed most.


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## saichele (Jun 20, 2007)

That's pretty interesting - take a bunch of PEX (or even irrigation tubing) and run it around the yard, then hook it up to the coil in the ductwork where the old AC would have been.  A small circulator pump, some PEX, and a ditchwitch and you're in business.  

Steve


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## Highbeam (Jun 20, 2007)

Welcome to a geothermal ground loop. This is a watercooled AC unit. Some folks use vertical wells to make the loops of pex go vertical and some have the space to do it with a ditch. I can link you folks to some actual project threads with pictures on a tractor forum where guys have done this themselves and it turned out great. There is hardware to buy of course but there is no outside air blowing unit and the ground temperature several feet down is the same year round so the heat pump becomes very efficient and silent.


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## TMonter (Jun 20, 2007)

> That’s pretty interesting - take a bunch of PEX (or even irrigation tubing) and run it around the yard, then hook it up to the coil in the ductwork where the old AC would have been.  A small circulator pump, some PEX, and a ditchwitch and you’re in business.
> 
> Steve



Problem is winter. You'd have to bury it at least 4 feet in the ground to prevent freezing. That's why the vertical wells are more common.


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## Highbeam (Jun 20, 2007)

No need to worry about freezing. They run a closed loop of antifreeze in them. I think it is methanol. Although you want to be deeper than the frost depth anyway. Deep enough that the ground is at the mean temp year round and that depth varies by region. I have seen some at seven feet deep. Certainly with the increased depth comes increased cost so there will be a point when drilling several wells and dipping the loops in groundwater will be cheaper.


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## jjbaer (Jun 22, 2007)

[quote author="Sandor" date="1182264403

Ok, I have a problem with that logic.

I strongly believe that the cost of energy, in every form, will be substantially higher 10 years from now than it is today.

If you believe otherwise, which your post suggests, then you are getting your "information" from Fox News and CNBC..[/quote]


Sandor,

I said no such thing........what I said was that buying a more efficient unit NOW immediately lowers electric bills dramatically..........so....even if energy costs rise, that with the new unit and higher energy costs, say, 5 yrs from now, your cooling bill 5 yrs from now will probably be lower than your cooling bill now at todays rates with the older energy hog..........


ex:  (energy hog A/C) x (todays elec rates) = $ Y cooling bill

(state-of-the-art A/C) x (elec costs 5 yrs from now) = less than $Y cooling bill

entirely possible even with rising energy rates......


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## jjbaer (Jun 22, 2007)

[quote author="Sandor" date="1182264403
So, if you think that electricity will still be cheap 10 years from now, I think that you really do not understand the magnitude of the problems that this (and many other countries) are facing.

.[/quote]


Sandor.....I agree that elec will not be cheap.....no argument there....my point is that buying a more efficient unit now to use at those higher rates we'll have in 5 yrs, will still result in a lower cooling bill (5 yrs from now) than the person is paying now (at todays lower rates but keeping the energy hog unit)......and it's due the increased efficiency of new units vs old ones....that's all I'm saying......so, the real question is this: how high do rates have to go to counteract the increased efficiency of the new unit? Answer: by the ratio of the efficiency (cooling vs elec used) of the new unit vs the old......if the new unit is twice as efficient as the old unit, then elec can double and the homeowner would get the same cooling bill they're getting now.........that's all I was saying....think we're on the same wavelength here.........sorry if any miscommunication.....


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## keyman512us (Jun 24, 2007)

Rhonemas said:
			
		

> I always wondered why they don't make smarter AC units.  Ones that detect what the outside temp & humidity is and adjust the "vent" accordingly.  I always thought a great idea would be one that's smart enough to recycle the inside air during the day when it's 80F+ outside and then automatically detects if the outside air is less than the house air (at night) it should open the vent and use outside air instead.  Maybe even detect if the outside air is much colder shut off the compressor all together and just turn into a window fan so to speak.  That would work well for those hot days and cold nights.
> 
> For outside units, why don't people make water cooled units?  Something like a ground source heat pump at a more simple level.  It's not usually hard to bury some stretches of PEX tubing and link it into outside units.  Water is much better than air at transferring energy so the outside unit could be small, and more efficient especially at noon using the ground instead of air to cool when it's needed most.



Rhonemas....
You bring up some very good points... Why "conventional" condensers are still the norm...is beyond me... After dealing with chillers and how they work... I would lean towards that technology. It only makes sense. You spend all the money, have all the equipment installed...and then try to waste the heat to air...doesn't make much sense when you think about it. Here in my locale most people have forced hot water heating systems...I'm surprised nobody has thought up a "conversion" method to turn the pipework into an AC system...It would be the same thing they do in commercial settings...just on a smaller scale. Not exactly a shrouded 40 foot tower with a 26' fan blade...being pushed by a 50HP motor, but...

Would be kinda cool... "Yup...thats my chilling tower...it's not a condenser"lol 

But then again...think of all those wasted BTU's in commercial and industrial apps. that "just get wasted...doesn't make a whole lot of sense. I'm sure big business is working with each other to "keep us in the dark". 

Luckily for me...I'm in an area where AC is only needed for a week or two out of the year. I rely heavily on a "whole house fan" setup. As of today...we have had a few days that have been hot and muggy but luckily we haven't hit a stretch of "hot days". Right now...with temps being "slightly less than average" I had to turn the fan off (it's kinda chilly right now). When temps are in the "mid range" I open two windows at night and the basement door for both fresh and cooler night air. During the day I keep the windows shut and the basement door open. (Luckily I have a "central" hallway on the northern side of the house) This allows fresh air to be exchanged into the basement, controlling the dampness and getting the hot air out of the attic.
 Now I know location is everything...what works for me here in New England....doesn't do someone in Virginia or Kansas much good... but getting the hot air out of the attic space, dropping it even a few degrees makes a big difference. When I first moved in to my house...summers were rough. I thought about just getting window AC units and bear it... Kinda funny, at the time...working as an apprentice electrician, I found myself spending a lot of time in peoples attics...and I quickly realized how hot that air really is. The boss sent me on a service call out of town. I drove by a big steel building that housed a trucking company...and they had pallets of old lighting fixtures...and half a dozen old "vent fans"...with a sign that said "Free". I got about a mile down the road and decided to turn around and check them out. I grabbed one, went to the service call and drove back towards the place. I thought to myself..."Maybe I should grab one more...I can put one in the attic, one in the basement..." nothin' doin'...when I drove back to the place...the fans were all gone! Needless to say I was glad I grabbed one...I took it home, hauled it up through the scuttle hole...opened the window in the attic, and plugged it in. BIG DIFFERENCE...right away. It keeps the basement moisture to a minimum, makes the attic "bearable", and keeps the whole rest of the house cool too. Every once in awhile you gotta lube the bearings and replace the belt. It does add $$$ to the light bill...but not as much as AC...and in my particular setup...is fairly quiet...

Something to keep in mind for the beginning and end of the cooling season...


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## Rhone (Jun 25, 2007)

Boy Keyman, you lucked out with the 'fairly quiet' fan.  I have a whole house fan, can't use it much.  I got a 36" 6900 CFM one, should've done my research first my house size calls for only 1,000 CFM.  The one I have even has the quieter "belt driven".  Even at low I'd compare its sound levels to that of a Harley Davidson idling in my house, with an unmistakable "Whomp, whomp, whomp" sound.  When you walk underneath it you can feel it trying to suck you off the floor.  My wife can't sleep with it on, and our 2 cats get the *$#! scared out of them and run around the house all night and over our bed we're trying to sleep in.  The moment we shut it off, the cats come to us looking exhausted from the experience.   My wife won't let me run it in spring because of her allergies, and in summer you know it's use is limited, leaving only fall.  Probably one of my worst investments, in part my fault.  Could I do it over I'd get the HV1000 which wouldn't require any rafters cut, has R22 insulation and seals air tight automatically when not in use, and the proper size.  The house fan I have now I use it so infrequently I go up there and remove my home made insulation cover when I want to use it, and put it back on when I don't.  That's no fun making me want to use it even less.  Mistake learned I guess.  

We currently use a 500 watt 5600 btu window AC exclusively, and try to avoid the compressor as much as possible.  Our house is well insulated, the window AC keeps our house 74F or less single-handedly, even when it's 90F+ outside for several days.  I believe it costs us $100/year in electricity to cool our house with it.


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## begreen (Jun 25, 2007)

Rhone, if it's belt driven is there a possibility of changing the pulley size on the motor to slow it down further?


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## Rhone (Jun 25, 2007)

I was thinking perhaps a rheostat to make the fan variable speed, I don't know if one would work with the belt driven motor or not.  There's also a limit to how slow I can make it, it has flappers that are opened by the suction of the fan and close when there isn't enough.


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## begreen (Jun 25, 2007)

I don't think a rheostat is the answer. 

First, is this a multispeed or single speed motor? If multispeed, what tap (speed)  is it on? Second, take a look at the motor pulley. Is it a fixed or variable pitch pulley? If variable pitch, try to set the pitch to the smallest diameter. If it's a fixed pulley, what is the diameter? See if you can change it for a pulley one half the current diameter. That will halve the rpm of the fan and I would expect it would still have enough push to open the shutters. If not, and this is a multispeed motor, then set it one speed higher. 

(PS: Isn't the fan blowing hot air out? If yes, I would expect the shutters to be controlled by the force blowing outward, not sucking inward.)


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