Why doesn't my airconditioner come on immediately every time

coloradobluesky

coloradobluesky

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coloradobluesky
I go over to my thermostat. Room temp is 78. Target temp is 80. So I turn the target temp down to 76 and the air conditioner (compressor/refrigerant type ie, not a swamp cooler) comes on.

Except sometimes. The electrician says I don't have Xcel's optional interrupter that they can install to reduce peak usage, so it's not that. Nor do I think it is the thermostat preventing a kid turning it off and on many times timer. It's not that either because it does it when it hasn't been touched in hours. Air conditioner installer just said it was normal, don't worry about it, although he didn't really know why either. Just said "these all do that now".

Anyone know why?
 
It doesn't like you.
Or:
It could be monitoring the load in your house and delaying the start until something else shuts down. Easily done with a couple of resistors and capacitors.
 
coloradobluesky said:
I go over to my thermostat. Room temp is 78. Target temp is 80. So I turn the target temp down to 76 and the air conditioner (compressor/refrigerant type ie, not a swamp cooler) comes on.
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On the times when it doesn't come on immediately, how long does it usually take to actually come on?

I believe some compressors are designed not to come right back on if they have only recently cut off. They need a bit of time for pressure to stabilize.
 
I know my parents A/C takes a few minutes to kick on after a temp change. However, my apartment A/C comes on while I'm still changing to the desired temp. I'm guessing it depends on the unit and the thermostat you have installed.
 
What is weird is it usually comes on immediately. But sometimes it takes 5 to 10 minutes to come on. And its not because its been running recently. Sometimes it doesn't come on immediately the first time it comes on that day (when I turn it on for the first time when I come home after being gone).
 
80°? In Colorado you should barely even need A/C.
 
coloradobluesky said:
What is weird is it usually comes on immediately. But sometimes it takes 5 to 10 minutes to come on. And its not because its been running recently. Sometimes it doesn't come on immediately the first time it comes on that day (when I turn it on for the first time when I come home after being gone).
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My upstairs A/C is like this. If I change the temp by a degree or 2 in summer or winter it will take 5-10 mins to kick on the compressor. Usually if I want it to kick on right away I need to change the temp by 4 degrees. Maybe you should try that.
 
It gets to 100 in Colorado in the summer occasionally, frequently gets to 90.
 
Our Trane has a humidity sensor. If you set it for a temp, you get the "feels like" temp. If I set for 74, typically the actual temp is 71-73. On really bad days, the spread is much greater.
 
It depends on how old your AC is. Mine is about 20 years old, there is a time delay relay that allows the condenser to run first for a number of seconds, then the air handler turns on. In my older system this is a time delay relay that was crapping the bed. The delay was not reliable anymore and sometimes it would come right on and other time it would take much longer until yesterday when it didn't come on at all. (not good, I found the evaporator completely iced and the lines iced too because the fan was not on.) I went to the AC dealer and $35 later problem solved, I put it in myself. We are probably done with the AC for this season here as today it was only about 64.
 
It might be an artifact that your AC unit is oversized and is short cycling. Ideally you want it to run for long periods of time then rest, so you get rid of the moisture. Otherwise you end up with a cold, clammy type of cool.

Unless you live in the desert, but if you do, you're probably using an evaporative cooler.
 
GlennAB1 said:
Change it from Auto to On and you'll not notice any lag/delay.
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You will notice a fairly pronounced sucking noise though. It shows up around the 9th of the month and looks like a bill.
 
MAKG1 said:
Virtually all control systems involving mechanical parts have a "dead band" to avoid cycling at high rates.
Click to expand...

This is pretty much it. It's also called hysteresis.

Essentially a time delay or dead band meant to prevent it from cycling too frequently.

Older thermostats would use resistor/capacitor circuits as timers and there are variations in them. New thermostats likely use integrated circuits which are more precise.





Or your air conditioner is possessed
 
JOhnH said:
I believe some compressors are designed not to come right back on if they have only recently cut off. They need a bit of time for pressure to stabilize.
Click to expand...

Likely This.

It's likely due to the "short cycle delay" on your compressor. Motors have a large in-rush current when they start and every time the motor starts the windings heat up with this increased electrical load and the windings stay pretty hot while running. Both frequent starts and starting too soon after stopping can burn up compressor components so there is a timer that keeps the unit from starting up until the windings have adequately cooled.

This timer is especially important to avoid damage when the power company is restoring power after an outage. Many times it'll take them two or three tries to get the line fuses to hold...the reason the power will come on and go back off multiple times as its being restored. This time delay keeps your AC from coming on each time and overheating.

As an aside, I will turn off the breakers to all other motor loads in the house when the lights go off. The fridge, the furnace, the air compressor in the shop, etc. and only turn them back on (one at a time) when I'm sure the power is back on and will remain on. This helps to avoid damage to those motors caused by multiple re-starts.

With today's electronic/computerized components, there may be a different reason for the delay, but the above is most likely. It likely DOESN'T have anything to do with the t-stat if it's intermittent...except that the short cycle delay programming might be in the t-stat.
 
coloradobluesky said:
I go over to my thermostat. Room temp is 78. Target temp is 80. So I turn the target temp down to 76 and the air conditioner (compressor/refrigerant type ie, not a swamp cooler) comes on.
Click to expand...

I re-read your OP...

Although, if your t-stat setting is initially 2dF higher than your room temp before you screw with it, then it wouldn't be very likely that the AC had just shut down. So, if this is an accurate statement, then it's likely not your short cycle protection and I have no freakin' idea what's going on.
 
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It is a commi plot, they started by fluoridation of our water and now time delay of ac so we have to suffer a minute longer in the heat making us thirst for fluoridated water.
 
Actually the reason for the delay is to allow the pressure to equalize between the high and low pressure sides of the compressor. The compressor is essentially a pump that moves freon through the system. Freon comes into the compressor as a gas under relatively low pressure and leaves at a much higher pressure, heat is removed in the condenser coil, where the high pressure gas condenses into a liquid as heat is rejected. It then moves to the evaporator (the cold part), where it goes through a valve or orifice and goes back into a gas, becoming very cold in the process. Here it collects the heat from your house and travels back to the compressor as a lower pressure gas.

If the compressor is turned off, then immediately turned back on, in most systems, the pressure is so high on the compressor exit side, that the compressor can't get going and stalls. This is bad for the compressor and can weaken the electrical coils eventually wrecking the compressor, hence the delay built into newer compressors.
 
Change your batteries?? Even though mine has 24v from the ac... mine started behaving oddly like this when the batteries got low. It's a $2 fix and never has happened since
 
hockeyrcks9901 said:
What?

AC vs DC has nothing to do with cost to run...
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From the interwebz:

"Why the upgrade? Most new high-efficiency furnaces include a “brushless DC” or sometimes called electronically commutated motor (ECM), which is much more efficient than the alternating current permanent split capacitor (PSC) motor that is in most of our homes, including most older high-efficiency furnaces. Historically it has been difficult to upgrade from a relatively inefficient PSC motor to a high efficiency ECM motor because the ECM motor requires different voltages as well as an advanced specialized control board, and these options were not available in a typical furnace. In recent years some companies have started offering retrofit packages which include strap-in compatible replacement ECM motors, and come with a fully compatible electronic control board to drive it. This makes the retrofit/upgrade relatively easy to accomplish. Although many of these upgrades cost well over $700 for parts alone."

I have DC motors on both of my AC units and leave them running 100% of the time during cooling season. This accomplishes two things:

1. It creates a slight draft in the house. A breeze feels cooler than still air thus allowing that-stat to be set a few degrees higher.

2. It prevents stratification of the temperatures. I have a very open floor plan, two story...and leaving the fans on will lower the second floor bedroom temps a good three of four degrees without lowering the t-stat

The downside is that I have to change my filters more often. The upside to that downside is that means the house is staying cleaner, albeit maybe only slightly.
 
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timwinters said:
From the interwebz:

"Why the upgrade? Most new high-efficiency furnaces include a “brushless DC” or sometimes called electronically commutated motor (ECM), which is much more efficient than the alternating current permanent split capacitor (PSC) motor that is in most of our homes, including most older high-efficiency furnaces. Historically it has been difficult to upgrade from a relatively inefficient PSC motor to a high efficiency ECM motor because the ECM motor requires different voltages as well as an advanced specialized control board, and these options were not available in a typical furnace. In recent years some companies have started offering retrofit packages which include strap-in compatible replacement ECM motors, and come with a fully compatible electronic control board to drive it. This makes the retrofit/upgrade relatively easy to accomplish. Although many of these upgrades cost well over $700 for parts alone."

I have DC motors on both of my AC units and leave them running 100% of the time during cooling season. This accomplishes two things:

1. It creates a slight draft in the house. A breeze feels cooler than still air thus allowing that-stat to be set a few degrees higher.

2. It prevents stratification of the temperatures. I have a very open floor plan, two story...and leaving the fans on will lower the second floor bedroom temps a good three of four degrees without lowering the t-stat

The downside is that I have to change my filters more often. The upside to that downside is that means the house is staying cleaner, albeit maybe only slightly.
Click to expand...


That's more a function of design of the speed control method rather than AC vs DC but I'll concede that I was coming at it from an Electrical Engineers perspective while in the air conditioning world they probably don't.

In large motors, DC motors are less efficient that AC squirrel cage motors as in a DC motor speed control is most often performed by using resistor banks to reduce voltage in turn wasting power while in an AC motor speed control can be done with frequency variation which does not waste power.
 
All of the above AND...

If you dig in and read the manual -- some cheap thermostats do everything in C behind the scenes and display in F. So your 2 degree change might not have been a big enough change in C to actually make the thing kick on.

In the manual for mine, stuff is done internally to .2 of a degree in C, which gives the stat a LOT more data to look at, and it compares the outdoor temp (which it can get from a hard wired local probe or amazingly, from NWS Internet weather sources via wifi) and also at the RATE of change indoors over the last few minutes -- it calculates that itself, but won't display it to the user -- to determine when to request heating or cooling.

It'll also ignore the user if it's in "profile" mode and not "manual" mode and the rate and direction match what it wants to do in the next 45 minutes. In other words, if the house is warming up in the morning and it knows we are leaving and it'll be in the "Away" profile, which isn't set to cool the house aggressively at all, it'll save the power of bothering to cool the house for the 45 minutes prior to the profile change.

In other words, if you have a REALLY dumb t-stat OR a REALLY smart one, it may simply be ignoring you. Ha. Read Mr. POH, and better, the maintenance manual if you can dig it up.

(How I determined mine is capable of seeing .2 degree C changes was by reading the TEST procedure for the stat if it's suspected to be malfunctioning. You have to get into a "secret" service menu to see that raw data.)

The only way to know for sure if a modern smart stat or a modern cheap stat from the One Hung Low factory in China is calling for heating or cooling, is simply to get out a multimeter and measure it and see.

And on mine, I can't even do that -- since it's talking to the furnace via serial data over the existing wiring that used to be used for a traditional t-stat, and not traditional contact closures like it's predecessor.

It even "learned" the cooling capability of our "dumb" AC system (you give it tonnage so it has an estimate to start from, and then it measures the real cooling capability over time and educates itself) since we didn't pop for the smart brand-specific heat pump which would have also talked to the stat over serial data passed through the furnace control board.
 
denverpilot said:
All of the above AND...

If you dig in and read the manual -- some cheap thermostats do everything in C behind the scenes and display in F. So your 2 degree change might not have been a big enough change in C to actually make the thing kick on.

In the manual for mine, stuff is done internally to .2 of a degree in C, which gives the stat a LOT more data to look at, and it compares the outdoor temp (which it can get from a hard wired local probe or amazingly, from NWS Internet weather sources via wifi) and also at the RATE of change indoors over the last few minutes -- it calculates that itself, but won't display it to the user -- to determine when to request heating or cooling.

It'll also ignore the user if it's in "profile" mode and not "manual" mode and the rate and direction match what it wants to do in the next 45 minutes. In other words, if the house is warming up in the morning and it knows we are leaving and it'll be in the "Away" profile, which isn't set to cool the house aggressively at all, it'll save the power of bothering to cool the house for the 45 minutes prior to the profile change.

In other words, if you have a REALLY dumb t-stat OR a REALLY smart one, it may simply be ignoring you. Ha. Read Mr. POH, and better, the maintenance manual if you can dig it up.

(How I determined mine is capable of seeing .2 degree C changes was by reading the TEST procedure for the stat if it's suspected to be malfunctioning. You have to get into a "secret" service menu to see that raw data.)

The only way to know for sure if a modern smart stat or a modern cheap stat from the One Hung Low factory in China is calling for heating or cooling, is simply to get out a multimeter and measure it and see.

And on mine, I can't even do that -- since it's talking to the furnace via serial data over the existing wiring that used to be used for a traditional t-stat, and not traditional contact closures like it's predecessor.

It even "learned" the cooling capability of our "dumb" AC system (you give it tonnage so it has an estimate to start from, and then it measures the real cooling capability over time and educates itself) since we didn't pop for the smart brand-specific heat pump which would have also talked to the stat over serial data passed through the furnace control board.
Click to expand...

My T-stat is similar to yours. It has learned the rate that my house naturally cools or heats based on outside temperature reported by the nearest NWS station and calculates whether it needs to do anything to reach the desired temperature at the desired time. It also has occupancy sensors in multiple rooms to determine if it even needs to reach the desired temp. If we're not home, what's the point in cooling the house? Or the opposite: if we aren't supposed to be home but it notices we are, then it tries to reach our desired temperature based on time of day.

Other cool features it has include multiple temp probes along with those multiple occupancy sensors to determine which rooms we're occupying and target that rooms temperature as the main control point. For example, if we're in the bedroom only then the thermostat only controls based on that temperature reading. If the living room is hot as hell but we're not in it then who cares. It also monitors the humidity and will run the AC if the humidity gets too high even if temperature is okay. Increasing comfort and keeping my house from getting musty.

It's pretty damn awesome how "smart" it is and how much more comfortable we are.
 
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