Air conditioning question

[cute fuzzy bunny]

So we've got this 17 year old Carrier system in the new house, and its actually surprised me by running pretty quiet and doing a decent job of cooling the place down in 100 degree weather. Surprising because my old mcmansion had a pair of Rheem systems (one for upstairs one for down) and they seemed to have a good deal of trouble on hot days.

Big question I have is that I've occasionally noticed when sitting in the living room, with the compressor outside the window, that the unit will spin up and then almost immediately spin back down. Later it'll come back on and run a while. So far hasnt seemed to be a problem, but i've noticed it often enough that its made it to my list of stuff to investigate.

We're going to replace the unit about 2 days after the 1 year home warranty expires.

My first thought is that the outside units of these generally come equipped with a shutoff switch that prevents the unit from being restarted shortly after a shutdown. Most good thermostats also have this feature. I've generally had an AC tech remove the restart/stop switch from the outside unit as its a frequent failure point and its redundant in the thermo.

This house appears to have an el cheapo $25 electronic thermo, and it doesnt look like the original. Guy who owned it before me was a cheap bastard who didnt spend a dime on anything.

So...any other reasons why I might get a 2 second spin and stop out of the outside unit other than the dumb thermo telling it to fire back up right after it shut down? I dont recall if the unit had been running shortly before its restart.

 

[USK Coastie]

It could be the internal overload inside the compresser can. These are ment to open if the windings overheat. They reset once the compressor cools off. Most carrier systems of that age did not have the antirecycle time on them. They relied on the thermal overload if someone rapidly cycled the thermostat.
You might consider going to the $39.95 electronic stat with the built in 5 minute time delay. Once the thermal overload gets tired it won't reset and you'll be changing out the AC unit or compressor.
If you install the new stat then change out the AC next year you won't have to buy another stat maybe.
I'd recommend a York or a Lennox as replacement. They are somewhat more $$ but worth it for their reliability.

 

[cute fuzzy bunny]

Thats about what I figured...I imagine the original therm owas swapped out by the former owner for the current el cheapo. I was going to try to hang on and get a new thermo with the new system next spring, but I guess its probably a good idea to blow the fifty bucks on something more worthwhile.

But then again, all this overheating might make the thing kick the bucket and I have 10 more months of home warranty left...

 

[mathjak107]

does everything go off when it stops? evaporatopr blower(the cold part) as well as the compressor?

you could also be a little low on refrig. after a while the unit gets cold and it pulls down and the pressure drops just low enough to trip the low pressure cut off. the unit turns off for a second ,pressure builds and it goes back on. you would have to be so close though to that point of trip that it just dosnt stay off or on.

 

[USK Coastie]

if the indoor unit stops as well as the outdoor unit it is most likely the stat. Most residential AC's do not have high and low pressure switches. They genneraly rely on the indoor coil turning into a block of ice then have it melt all over the home owners furnace room/new carpet.

 

[samclem]

Would there be any downside to installing a good thermostat right now? You could get the features you want (setback, etc) and it might help the present AC unit survive the summer by incorporating the normal time delay feature. When you get the new AC unit you'd keep the deluxe thermostat. Just be sure you buy a thermostat that will allow you to incorporate all the best things that the new heating/cooling units have (e.g. maybe a multi-speed blower, multi-stage control for the furnace, etc).

 

[cute fuzzy bunny]

I'd just be out fifty bucks. Maybe a hundred if I get one with all the bells and whistles.

I'd be okay with it throwing a rod and getting it replaced by AHS. As long as it doesnt die due to bad maintenance. Low refrigerant might be seen as bad maintenance.

That the outside unit was about 1/4 buried in dirt and woodchips might be too...although it sure was quiet that way. I dug it out and built a retaining wall next to it to prevent a recurrence. but theres enough dirt and rust marks on it to make it obvious...

I think most new systems come with a branded thermostat as part of the package. At least the higher end high efficiency systems I'd be looking at.

But then again, it'd suck to have it drop dead in the next month or two when its going to regularly be 100 out.

 

[cute fuzzy bunny]

Oh fooey, now i'm looking at $200-250 wireless thermostats.

I have a small zoning problem...this house is basically three stories and the thermo is downstairs in the coolest spot in the house. Which means insufferably hot upstairs both summer and winter.

Some of these units allow a receiver in one place (where the current thermo is) and up to 4 remote wireless units in various parts of the house.

Seems the transmitter parts eat batteries. Not sure if there are any other big downsides...more investigation as I go.

 

[cute fuzzy bunny]

Like this: Totaline Wireless Thermostat System - No Need to Rewire

 

[samclem]

Like this: Totaline Wireless Thermostat System - No Need to Rewire

Hmmm. If you had 4 thermostat sensors and a simple AC system, I guess the AC would just come on whenever any sensor hit the set point. So, one part of the house would still be freezing to make the top floor comfortably cool. As you said, you've got a zoning problem, which sounds like you'd need either multiple AC/furnace units or sensors/dampers (which are a PITA).

Dumb question: Is it sufficiently comfortable if you set the fan to run continuously? That uses some electricity, but sometimes it is enough to get the temps close to the same throughout the house. Plus, IIRC, your DW has allergy issues, and this helps run the air through the filter more frequently, which (some folks believe) helps cut down on dust/allergens if you have a good filter.

Or, to have the best story to report, you could plumb in a purpose-built point-to-point duct from a spot on the top floor to a spot on the lowest floor. Put a small fan in there and have a some fun building your own temp sensor/logic controller to push air when the differential is sufficient. Put in a HEPA filter (which is practical in a low-flow situation like this, it is NOT practical in a furnace/AC system) and you'd be doing some real air cleaning and developing a new hobby to boot.

 

[cute fuzzy bunny]

Thats the interesting part about the wireless therm I linked to. You can carry it around the house with you, so the room you're in is kept to your comfort temp. That'll end up with the downstairs being cooler both in the summer and winter than the upstairs...when we have the thermo upstairs...which is when we're all in bed. Not as efficient as a true multizone which would keep the whole house even...but a shitload cheaper for capital outlay. A lot of ducts in this house...reducting and putting in dampening vent covers would run a few bucks.

I put the kill-a-watt on our unit with just the fan running. I forget what the reading was but I remember the expletives I spit out...it was pretty high. 150-180 watts...something like that.

The furnace filters are just ineffective IMO. I've done a lot of research on them. Most of your allergens are in the carpet, bedding and furniture. They poof up when you disturb them, then mostly settle back to the floor. They're just not going to make it up 10' to the air return grill to be filtered. Plus its not that helpful to filter air when you've got 300lbs of dogs and 50lbs of cats sleeping under your nose... Plus we get lousy air flow with filtretes in...I tried them in this house and the last two.


Funny you should mention a separate circulation system...it occurred to me that our master closet upstairs shares a wall with the 3 story high ceilinged sitting room
downstairs at pretty much the opposite end of the house. I was pondering cutting and framing a 12" pass through and using something like a high flow, low watt, low sones bathroom type exhaust fan to continuously and rotationally circulate air through the house 24x7.

Then I was advised by the wife that I wont be poking any more holes in the walls or ceilings anytime soon.

I guess that hole I cut in the garage ceiling in our old house and then left that way for 2 1/2 years is coming back to bite me now...

 

[samclem]

...it occurred to me that our master closet upstairs shares a wall with the 3 story high ceilinged sitting room
downstairs at pretty much the opposite end of the house. I was pondering cutting and framing a 12" pass through and using something like a high flow, low watt, low sones bathroom type exhaust fan to continuously and rotationally circulate air through the house 24x7.

Then I was advised by the wife that I wont be poking any more holes in the walls or ceilings anytime soon.

She's a killjoy!
Well, if DW relents and lets you do this later, be sure to incorporate some soundproofing. Building a direct auditory "window" from your bedroom to a sitting room downstairs could lead to some interesting situations. You might end up having that little father/son chat with Gabe a few years earlier than you'd planned . . .

 

[USK Coastie]

How about a Mini Split system for the Master Bedroom? Blow through an outside wall and down the side of the house to the ground for the condensing unit. Then fur in and trim the line set going down th side of the house.

 

[cute fuzzy bunny]

Thought about it.

The existing single unit is plenty capable of cooling (and heating) the whole property...its the thermostat location that seems most at issue.


Big problems come around at night. Master suite is under the big warm attic while the thermo is downstairs in the cool living room. Same problem in the winter...downstairs is chilly so we get blasted with excessive warm air upstairs.

With the therm set to 75 downstairs (heat or cool) its around 80 upstairs except when the unit is on and running.

Sooo...having the thermo upstairs would cause more a/c usage in the summer, and less heat usage in the winter.

Right now i'm combating the warming upstairs by running the whole house fan...but in a couple of weeks when its 100 during the day and 80-something at night, thats not going to help much.

 

[Nords]

The existing single unit is plenty capable of cooling (and heating) the whole property...its the thermostat location that seems most at issue.
Big problems come around at night. Master suite is under the big warm attic while the thermo is downstairs in the cool living room. Same problem in the winter...downstairs is chilly so we get blasted with excessive warm air upstairs.
With the therm set to 75 downstairs (heat or cool) its around 80 upstairs except when the unit is on and running.
Sooo...having the thermo upstairs would cause more a/c usage in the summer, and less heat usage in the winter.

I'm impressed that wireless thermostats allow yet another way for guys to both carry around another remote control and to annoy their spouses! Is America a great country or what?!?

As for the "big warm attic", I thought insulation was supposed to keep that from happening. I don't have any experience with the big puffy stuff or the truckloads of cellulose, but we use lots of "radiant foil" insulation to keep the heat out.

Otherwise you're going to get the upstairs at the perfect temperature and then have to rebalance the heck out of the rest of the house's ventilation system to keep it from turning into a meat locker.

 

[cute fuzzy bunny]

You're apparently unfamiliar with californias central valley...

We're only about four feet from the surface of the sun here.

Radiant barriers lose effectiveness (supposedly) after 3-5 years due to dust collection.

I could increase the r-value in the attic, but we're getting hit in the upstairs on all the walls and you can just lay your hand a foot in front of them and feel the heat coming through.

The meat locker thing shouldnt be a huge problem...once the system kicks in the warm air from upstairs gets recirculated downstairs. The only real problem happens when the air stops moving, its staying nice and cool downstairs, and the heat builds up upstairs. A whole floor acts as a nice thermal insulating layer. Until you want to sleep up there.

Only trouble i'm having is finding one of these wireless dingy's available for sale locally. I'd like to take it back if I dont like it.

 

[Nords]

You're apparently unfamiliar with californias central valley...
We're only about four feet from the surface of the sun here.

You knew that already and you still bought another home there?!?

Radiant barriers lose effectiveness (supposedly) after 3-5 years due to dust collection.

Well, I can vouch that it's good after three years but I'll have to get back to you in a couple years on the rest of it. I wonder who paid for that study!

Some of our insulation is stapled to the inside of a garage door. Hard to see how the side exposed to the garage door is getting dusty.

I could increase the r-value in the attic, but we're getting hit in the upstairs on all the walls and you can just lay your hand a foot in front of them and feel the heat coming through.

That was exactly our problem until we started using the foil. Along with crawling all through our attics stapling the foil to the underside of the tops of the trusses (something you can't do if there's snow in winter) we also stuck it between the studs of every wallspace we could reach. We also did the same to an outside wall (other side of our headboard) when we were repairing a roof flashing leak. We just stuffed 28"-wide strips of it up into the framing voids from the bottom as high as we could reach and it's a tremendous improvement. The foil makes such a huge difference (15-20 degrees) that we're contemplating ripping the house's south-side sheathing off just to insert a couple hundred bucks of foil. However there may be a better way (like sprayed-in cellulose or a pergola) so we have yet to make a decision.

If you can reach behind the drywall or the sheathing of any of those hot walls, give it a shot. The stuff is cheap!

 

[cute fuzzy bunny]

You knew that already and you still bought another home there?!?

Well we've already established that i'm an idiot.

I wonder who paid for that study!

YOU did!
http://www.ornl.gov/sci/roofs+walls/radiant/index.html

Not sure if its in this report, but i've seen that non horizontal applications are less efficient and truss mounted arrangements lead to reductions in roofing life. They actually sell sheathing with the barrier already installed on the bottom. Its offered by many new home builders and some re-roofers, but the locals consider it another variant of 'snake oil'. Take that with a grain of salt...

 

[Nords]

Not sure if its in this report, but i've seen that non horizontal applications are less efficient and truss mounted arrangements lead to reductions in roofing life. They actually sell sheathing with the barrier already installed on the bottom. Its offered by many new home builders and some re-roofers, but the locals consider it another variant of 'snake oil'. Take that with a grain of salt...

Well, again I'll have to get back to you in a decade or two on the roofing life. No problems so far.

If we were to re-roof tomorrow then we'd rip everything off down to the trusses and start with some type of structural insulated panel. (As soon as our bunny goes to his great reward, our familyroom will be starting a new life.) We'd also rebuild south-facing walls with thermal barriers. I don't know if it's common practice among local builders but we see an occasional "thermally smart home" article in the newspaper (especially in places like Waianae & Ewa) and there are three or four businesses at every home show.

But we're just tweaking on a good-enough situation. I'm not the one paying the A/C bills or posting in a pool of my own sweat!

 

[cute fuzzy bunny]

As soon as our bunny goes to his great reward

I wish you'd stop bringing that up.

 

[cute fuzzy bunny]

I put the kill-a-watt on our unit with just the fan running. I forget what the reading was but I remember the expletives I spit out...it was pretty high. 150-180 watts...something like that.

Wow was that freaking wrong. Just checked it again and its 700 watts. Our old one (only 8 years old) was 533 running just the fan.

It might be time for a new furnace and air conditioner a little sooner than I thought...

 

[HFWR]

When I replaced my AC unit, anything above a 12 SEER had a two-stage fan. However, the cost went from $3k-ish to >$7k...

A problem I have is, after the system has been off for a time, then kicks on, the first several seconds consists of all the hot air (duct work in attic) being cleared from the ducts, sometimes RAISING the temp in the house a degree or two...

If I wasn't so lazy, the fan on my current furnace (which serves as air handler for both heat and AC) has a half speed tap. With a fairly simple solenoid switch and some minor circuitry, I could run the fan at half-speed while the compressor is off, recirculating the air in the ductwork, and preventing excessive heat build-up, and saving at least a few bucks in electricity over leaving the fan running at full speed all the time...

 

[cute fuzzy bunny]

Wouldnt you actually be making it worse? Right now you're getting an insulative heat leak into the ducts in the attic that probably hits a certain point and remains there. If you ran air through it all the time, wouldnt you suffer a continuous insulative heat gain spread across all the air in the house as its run through?

 

[HFWR]

Beats the heck outta me... I just figured keeping the air moving would limit the temp swings.

 

[cute fuzzy bunny]

It'd keep the temps more regulated and consistent...