Carrier Heat Pump Cycling - Too Fast?

[jmyshral]

Hello, we live in Northern Virginia bought a house this summer that has a Carrier heat pump, which is less than 10 years old. It is my first heat pump, so I am not sure if it is working properly.

Here are the model numbers / specs:
Indoor Fan Coil - FV4ANF003
Auxiliary Electric Heater - KFCEH1501F15 - 15KW
Outdoor Unit - 38YXA036300 - 36,000 BTUs
Thermostat - Non-programmable Carrier Heat Pump (w eHeat)

So here's the problem - when set on heat (71 degrees thermostat; 40-55 degrees outdoors), the heat pump cycles very frequently. It starts up every 14 minutes and 6 seconds (to the second), and runs for 3 minutes, then shuts down for 11 minutes. It does this repeatedly over and over and you can almost set your watch to it. It will never run for longer than 3 minutes. The thermostat does not move - it is usually between 70-71 degrees the whole time.

I've tried adjusting some of the settings on the "Easy Select Board" but this does not change the frequency of startup or running. Also there does not appear to be a threshold setting for my thermostat to set a wider band; I have read somewhere that the default threshold should be 2 degrees, whereas my room temperature is barely fluctuating by 0.5 degrees according to a more precise thermometer. Also, since it is happening every 14 minutes and 6 seconds, it does not seem tied to temperature, but rather to a timer.

Is this normal operation? It seems like way too much wear and tear on the heat pump when it should just run longer than 3 minutes at a time and start up less frequently.

My second question is how do you make the startup quieter? When the outdoor unit kicks in, it starts with a loud thud - presumably from the initial torque of the fan starting. The fan itself turns very easily, but the initial startup is very loud.

Please let me know if either of these are problems that can be fixed. I have taken some video footage that I could upload to YouTube if it would help diagnose the problem.

Thanks,
Mike

[dac122]

Mike,

I think most would agree this is short cycling and yes it is putting added wear and tear on the unit. It sound very much like this is a thermostat issue. Did you have this issue when in cooling mode?

[Jay11J]

Do you have a model # on the t-stat?

Is there a vent blowing on/near the t-stat?

[jmyshral]

Thanks for your responses. This "short cycle" problem was not occurring when we had it set on AC mode during the summer. I have only noticed it since we switched to heat, and more particularly as the temperature has gotten colder I have noticed the cycling.

There are a few numbers on the thermostat, but I'm not sure which is the model number. It is a Carrier, and on the inside it says 960-120011-2 ABS and the printed circuit board says TSTATCCNHP01-B. I think this is what it looks like -
http://img148.imageshack.us/img148/1...ttstatcau4.jpg

Also, the vent in the room is closed, and it is a good 12 feet away from the thermostat so there is no way that it is blowing on it.

Thanks,
Mike

[jmyshral]

I found the following manual for my thermostat - http://www.docs.hvacpartners.com/idc...tstat-16si.pdf

I checked all the settings, and they were all set to factory defaults. I decided to change Option 1, the "Anticipator Adjustment" from the factory default of 3 to a higher value of 6. According to the manual, "Higher numbers decrease the sensitivity and slow the cycle rate... However, a limiting feature will not allow more than 4 equipment cycles per hr, regardless of setting". However, this did not seem to fix my problem since I am still getting cycles every 14 minutes (which seems to be the maximum of 4 per hour). Again, the unit is only running for about 3 minutes of each 14 minute cycle.

There is another section in the manual called "Operational Information", listing a bunch of timer conditions:

Five-minute Compressor Timeguard
This timer prevents the compressor from starting unless it has been off for at least 5 minutes. It can be defeated for 1 cycle by simultaneously pressing the FAN mode button and the INCREASE TEMPERATURE button.

Fifteen-minute Cycle Timer
This timer prevents the start of a heating or cooling cycle until at least 15 minutes after the last start of the same cycle. Its function is to assure that equipment is not cycled more than 4 times per hr. This timer is defeated for 1 cycle when the desired temperature is manually changed. It can also be defeated for 1 cycle by simultaneously pressing the FAN mode button and the INCREASE TEMPERATURE button.

Fifteen-minute Staging Timer
In multistage heating or cooling, this timer prevents any higher stage from turning on until the preceding stage has been on for 15 minutes. This timer is defeated if the temperature error is greater than 5°F (usually due to a large change in desired temperature).

Three-minute Minimum On Time
In normal operation, when a stage turns on, it will not turn off for a minimum of 3 minutes.

Heat/Cool Set Points (Desired Temperatures)
A minimum difference of 2°F is enforced between heating and cooling set points. This is done by allowing one setting to "push" the other, to maintain this difference.

Auto Changeover
When the auto changeover mode is selected, a change from heat to cool (or vice versa) will not occur until an opposite mode demand has existed for 20 minutes. If the set point is changed, the 20 minute requirement is deleted. Auto mode may be disabled.

Emergency Heat Mode
When thermostat is configured as a heat pump and emergency heat mode is selected, all Y signals are locked out and W becomes energized upon a call for heat.

Heat On and Cool On Icons
When a heating or cooling demand exists, the HEAT ON or COOL ON icon will either remain on or flash. If flashing, the equipment is temporarily prevented from turning on by one of the timers (see above). While the icon remains on without flashing, the equipment is on.

I have noticed that the heat pump stops after 3 minutes and the "HEAT ON" icon is flashing, which I guess means one of these timer conditions has kicked in. But which one?

Thanks,
Mike

[dac122]

What are Five-minute Compressor Timeguard, Fifteen-minute Cycle Timer, Fifteen-minute Stage Timer, Three-minute Minimum On Time set to? Maybe something conflicts, or you have a bad thermostat.

Also, try holding the Fan and increasing the temp before the heating light begins blinking, or you can try jacking the temp more than 5°.

Finally you may be able to reset the thermostat back to factory settings if there is a way to do that. Just write down every setting before doing that.

Let us know what you find.

[jmyshral]

OK - So I did some more testing over the weekend. First, to answer dac122's questions - the timers he mentioned are all hard coded and cannot be changed (Five-minute Compressor Timeguard, Fifteen-minute Cycle Timer, Fifteen-minute Stage Timer, Three-minute Minimum On Time).

I did, however, adjust the Anticipator Adjustment further upward to 8 out of 9, hoping to reduce the number of cycles per hour. However, no matter what I set it to, I was still getting the system to turn on about every 14 minutes and 6 seconds, and the heat pump would run usually the minimum 3 minutes, but sometimes as much as 5 minutes at a time.

I was able to "override" the timers by holding the fan and the up arrow, which ran the system for 30 minutes. However, I may have set the temp too high since the auxiliary heat strip kicked in and pumped out some hotter air.

I also placed a more accurate thermometer next to the thermostat. The accurate thermometer showed a very slight variation - less than one degree - while the thermostat was jumping from 69 -70 - 71 degrees every couple of minutes. I also programmed a 2 degree "offset" into the thermostat to help calibrate the readings closer to the accurate thermometer, but the thermostat still floated a couple of degrees.

Therefore I am guessing that the thermostat is just not accurate enough, and is likely falling below the setpoint during a 15-minute (14:06) minute interval, and causing the system to run the minimum 3 minutes when the timer expires. This is resulting in the short cycling, but does not explain why the anticipator adjustment had no effect.

So, since the heat pump and blower seem to be working fine, I think it is worthwhile to try a new thermostat, and upgrade to a programmable model at the same time. Based on what I have read, I would like to limit it to 2 cycles per hour, with a 1-2 degree differential. Based on these parameters, what is the best choice for a 2-stage heat pump programmable thermostat?

Thanks,
Mike

[dac122]

Mike,

Given what you've tried and the results I would say your tstat is bad. As far as replacements go I'd pick Honeywell due to overwhelming familiarity of folks with that brand, and support they can give and others on forums can provide. There are a number of models that provide 2 heat 1 cool to pick from, so I would suggest reading the manuals to know which one is to your liking, or just compare them side by side at a Home Depot.

Let us know if you need anything else.

[TigerDunes]

jmyshral

how old is system?

You have a nice system that includes a VS air handler. I would have it checked out by an authorized Carrier dealer, perhaps the dealer that installed it. And while the HW stats are fine, you live in an area with high summertime humidity. If this was my system, I would look at the Carrier Edge thermidistat that has the "dehumidify on demand" feature.

IMO
Good Luck!

[Jay11J]

I would suggest the Honeywell IAQ. If you don't have enough wire in the wall to support the staging or dehumid hook up, the IAQ use 3 wires, and EIM is mounted next to the air handler.

And you can install outdoor sensor on this and lock out the Aux heat when you really don't need it.

[jmyshral]

Thanks for the recommendations. I think the system was installed in 1999 and just turned 10 years old.

I do agree that it would be nice to control the humidity as well. But will I need to install a humidifier in order for a "Thermidistat" to work? Or will the variable speed nature of the air handler help with dehumidifying, and I would just lose the humidifying feature?

I came across this fancy Bryant/Carrier stat on eBay - DIGITAL PROGRAMMABLE THERMOSTAT SAVE BIG!!!!! FREE SHIP - eBay (item 330374983968 end time Nov-13-09 13:10:56 PST)

It appears to be the Bryant version of the Carrier Edge thermidistat and comes with wireless outdoor sensor. Seems like a good price - would this work for me? I'm not sure I should pay over $200 for a Carrier or Honeywell if I could get this for $90.

[Jay11J]

You don't need to add anything, just wire up the t-stat the correct way, and set up the air handler to run with that set up.


You have enough wire in the wall to support this?

[jmyshral]

I'm not sure if there are enough wires to control this. Right now I have a 6 wire system: R, Y/Y2, G, C, W/W1, O/W2. Is this enough or will the humidity controls require additional wires?

Also, the manual for the Bryant T6-PRH has a 2-wire option as follows:

Two--Piece Thermostat Configuration
The Preferred Series AC/HP Control can be installed in one of two configurations. The control may be installed as a single--piece thermostat or it may be split into two pieces and mounted in separate locations. As a single--piece unit, all required wiring must be brought to the Equipment Control Module for connection to the terminal strip. In two--piece configuration, the Display Module can be mounted in the living space while the Equipment Control Module may be mounted near the indoor furnace or fan coil. Connection from the display to the Equipment Control Module requires only two wires. All other control wires are connected to the Equipment Control Module from the HVAC equipment. This configuration results in a slimmer display and locates the Equipment Control Module containing the switching relays away from the main living space where relay clicking will not be heard.

I assume if I do not have enough wires in the wall, I could use this two-piece configuration and just use 2 wires in the wall and wire the rest of the wires to the ECM next to the air handler?

[Jay11J]

Old-------New
R---------Rc/Rh
Y/Y2------Y/Y2
G---------G
C---------G
W/W1----W/W2
O/W2----O/W2/B

You are a wire short for the dehumd.

I would do a remote set up, EIM on the air handler, then get a new t-stat wire from that to the furnace.