Hi all,

I asked this question last year, but i just have to ask it again. Two years ago our AC broke down, it was finally fixed but never behaved the same. The entire operation of it is way different than what i remember, but then, it might be the age of the unit, which is 15 years. It's a Ruud unit, if it maters. Our bill doubled since then. We are now at 350 bucks a month, cooling down a 1100 square house, with thermal curtains on all windows (we live like a vampires, trying to keep windows cool), and running our Ac at 83 degrees, up until 9 pm, which is when we lower it to 81.
My boss who runs a warehouse and 2500 square feet office space pays 470, while keeping our AC at constant 77 and running 4 coolers in warehouse. I can't believe that we are only a hundred below that, while suffering. I also have afriend with older Ac unit, and they also keep theirs at 83/81 and her bill is 190 which is what we used to pay before it broke down. Blower motor was changed 2 years ago, but like i said this AC has been running funny since then.
What keeps happening is that it will run for 20 minutes at 83, shut off, and then come on again in 2-3 minutes. Before, it would run, shut off for 20 and then come on again, but somehow our AC keeps running and running. If i put the thermostat to 85, it will take 20-30 minutes to kick in, but once it does, it will run on the same , almost non-stop cycle.
This was not the behavior i remember before blower motor died and it's driving me nuts. I had guys look at it, they claim nothings wrong with it other than being older unit. Thermostat is brand new, changed two weeks ago, no changes whatsoever.
Any suggestions? I would really appreciate it, i feel like i am going crazy!

 

What is your AC's Delta-T ? ( which is the temperature split between register input air and return air. ). one more item to check. is airflow strong ? same as your old blower fan airflow ? Also you must keep your coil and filter clean.

 

I am not convinced that air flow is the same. Our AC guy claims that we have appropriate blower motor, and i called him again two weeks ago to go on the roof and check. I was willing to buy a new one. He came down telling us that the blower motor is correct 3/4 HP. I am not buying it though, since 2 years ago he installed non-original blower unit and himself stated that it isn't strong enough and we will eventually need new one. Is there a way for an amateur to check on HP of the blower motor, without having to take things off up there? Could i do it as a woman?
Also what is the right way to check on that Delta T?

Thanks

 

The HP rating of the motor should be clearly stated on the label attached to the motor. The only difficulty you may encounter is that you may need to pull out the blower assembly to access the motor to read the label. There are two specifications, apart from the physical mounting, that you need to be concerned with. They are, the horsepower rating, and the RPM. While you may have the correct HP rating, if the RPM is too low, it won't move enough air. Also, be aware that some motors are multi-speed. They can run at different speeds depending upon what motor tap is used. It's not uncommon for the heating and cooling modes to use different blower speeds.

 

To check Delta-T, hold a thermometer (2 inches) in front of the input cold air register and get the air temperature reading, then use the same thermometer put (1 foot) in front of the return air register and get the reading. the difference of two temperature readings is your Delta-T (we like to see somewhere around 15 to 19). For airflow, a simple question first, can you feel the cold air 8-10 feet away from the register ?

 

In our 2 bedrooms we can feel airflow from that distance. The rest of the house, which is the furthest distance from the AC location on the roof,we can barely feel anything. Our living room is super hot. Kitchen with family room too, and in the laundry room (which is on the opposite side of the house from the bedrooms), there is almost no airflow coming from the vent. Also what i noticed in the last two years, is that we have double vents on the wall, but air is coming only from one side of the went, and not the whole length of it. So i would say that one side of the house is much colder than the other.
I will measure the air temperature difference in the morning, i am not sure if we have thermometer around any longer. Could this be matter of AC being too old or simply a blower motor not being adequate? I don't remember our Ac unit needing an hour to cool down a one degree in the house, nor i remember it working almost non-stop.

 

I won't get technical, but just because it's old doesn't mean it shouldn't work. The one at my old place is original from 1990 and it works just fine for a 1600sf home. If yours worked before, broke down and was repaired, but won't maintain temps, then it still has an issue.

Your bill is horrendous. We don't have quite as hot temps up here as you do, but I never paid over about $190 with the stat set at 75-76.

 

From what you just said, you have unbalanced airflow issue. Did you have this problem before (with the old fan) ? As mentioned, $350/m for a 1100 sq ft house (with Tstat set at 83 degree) is not acceptable even the system is old. Also, from stop to start only 2-3 minutes, that is another issue which has nothing to do with the blower fan. Anyway, try to get the delta-t from both bed room and living room and post them here, hopefully we can figure out something.

 

Ok, so i decided to time the AC and its intervals, and this is what i've got:

On 83 degrees:
Off at 2:41 Pm
On at 2:47 Pm
Off at 2:58 Pm

I got up raised the temp to 84 degrees when it turned off
On at 3:12 pm
Off at 3:18
On at 3:27
Off at 3:33

It seems that no matter what temp i set it to it will take this rhythm and cycle it, whereas before breaking it would need much longer to turn on after shutting off on these temps. No wonder our bill is sky high.
I do not have anything to measure Delta T points right now, until i go to the store on weekend. Just for the sake of additional information i want to mention that reason for AC breaking down 2 years ago was unbalanced fan which we kept running until we had money to fix it (it was middle of summer here in AZ). The entire house felt like an earthquake or war zone. Blower motor got stolen by a first technician who changed a fee on us by doubling it up there on the roof. We said no to that cost and he took off with the motor. Then other guy came put new fan, new blower wheel and "Universal blower motor", new capacitor and from that point on our bill doubled.

Would duct leak cause Ac to cycle like this? Maybe something else got messed up due to shaking from unbalanced wheel?
Also he said we have a very, very slow Freon leak, and he recharged it, but all in all he stated that we will need new unit in 1-2 years.

Thank you for helping, i would really like to solve the mystery. I have a feeling that next year we will have even higher bills.

 

One thing that isn't clear to me is whether the A/C system is able to maintain the desired temperature with the cycling. For instance, if you set the thermostat for 75, and it was currently 85 in the house, does the system continue to cycle on/off or would it stay on for hours, trying to bring the temperature down?

 

Bob,

I think with me setting it to 75 degrees, it would take at least 4-5 hours to bring it down to that temp.
If i set temperature to 80-81, it will cycle, the exact same way it always does. That is the thing that puzzles me. Usually we set it down to 81 at bed time, and it takes over an hour for it to cool down to that temp from 83. from that point on it will continue it's treacherous cycle of running long and shutting off super short.
2 years ago, if i set my thermostat at 84, it would come on for couple of minutes and shut off for 20 or more. Now, no matter how high it's set, even if it was 87, it will do same cycle. It seems to be running on 6-10, 6 minutes off then running for 10 or more. The hotter it gets, the shorter the shut-off time is, and longer it takes to cool the room down.

 

Looks like you have 3 or may be 4 different problems: (1) unbalanced airflow caused by improper duct work. Air duct size, distance must be all considered. (2)Weak airflow can be caused by dirty filter or coil, air leak, or a weak blower fan. (3) Took long time to cool the rooms down is caused by weak AC which may be caused by low Freon charge or duct air leak (this can be verified by Delta-T). (4) Cycle-on too soon is related to your house's overall insulation and outside temp(not AC), that is why the cycle time is almost the same no matter what temperature you set on your T-stat.

 

I think we can write off duct work and duct size, just due to the fact that it used to work properly until it broke down. Blower fan was purchased brand new according to the manufacturers specs.At least i think so, because i have to trust Rheem. At least i think so...
Is there a way for us to check for a leak or we have to call someone?

 

You really need to do at least the basic Delta-T, before moving on to other things if it's 15-19 degrees, then your system is probably not leaking. Then airflow would be next, a good tech will have a little meter that he can measure airflow with.

I have to relate this, but I doubt it's your issue. Got tired of high bills back in VA and bought a digital stat as a first step. Unfortunately I bought a cheap programmable stat (what did I know?). Put it on, put in some minor setbacks for while at work and thought great, next month will be better. Not only wasn't better, was higher and the house wasn't as comfortable. Took the setbacks out, but it still wouldn't kick on until the sun was fully up around 10 AM and the A/C would run constantly til 7PM.

Called a tech and as soon as he saw the stat, he said I think I know your problem. Gave me a list of better stats, checked airflow and Delta T and said those looked fine. New stat, I could set the temp and the setbacks and the bill was cheaper and the unit would run maybe on 20 off 30.

One problem with setbacks for A/C as the pros will confirm I believe, it runs most efficiently if runs longer and is off longer. Remember, A/C has to cool down the walls, furniture, floors, etc. Otherwise, as soon as it shuts off, those things immediately start heating the air, which is what you feel. Longer runs are also better for humidity control...not that you probably have that issue most of the year.

Setbacks are great for heat, not so much for A/C.

I also wonder about such a high temp setting. Is that just because of the high bills or have you always had it that high even before the repair?

 

I will measure the Delta T as soon as i get something to measure it with. What would be the best and cheapest option?
Our AC guy measured all of this with a little gun looking, laser thing and said it's all good, but i will do it myself.
We had a programmable thermostat that was at least 15 years old, and i somehow managed to enter it's internal factory settings and i screwed some of them up. One of the settings altered the temperature reading, i don't quite remember it but you could set the thermostat to sense either +1 or -1. Since it was running constantly after the repair i might have set it up to +1, thinking it will run less, but that didn't happen. Little square box showed up on the digital display and i could never remove it. Even when we lost power or took the thermostat off the wall, that little square always came back.
Two weeks ago after losing power and having to adjust all the settings on the thermostat yet again, i called our guy and told him to install a simple one, ON, OFF, Cool and Heat thermostat, hoping it will solve the issue (i blamed our AC misbehaving on the old, altered thermostat), but that never happened. AC still runs the same, if not longer, because with these simple thermostats i think what happens is that they HOLD the temp or something.
I don't know, i am just lost for words. Last night the temperature here in Phoenix went down from 104 to 90, i put my AC down from 83 to 81, went to bed, and i was just laying there listening to it run without stopping for at least an hour. Then it finally shut off, and came back instantly and kept running for at least half an hour. I got up, put it on 82 and it shut off long enough for me to fall asleep without going insane.
The reason we are keeping it this high is due to bills, partially, but i've always kept it at 83 during the day because i am always cold. Before, when our bills were normal we would put it down to 79-80 when husband comes from work in the afternoon, and we'd keep it there until the morning. It worked normally, it would cool for a while then shut off for extended periods, never like this.
I just realized last night that some blower motors are 3 speed and some single. If we somehow got weaker blower like i know we did, and it's either single speed or something like that, could it cause this issue of AC running like this?