Author Topic: AIR CONDITIONER DELAY IN STARTING  (Read 31395 times)

LEAH DRAPER

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AIR CONDITIONER DELAY IN STARTING
« on: July 07, 2015, 02:36:05 PM »
Why is there a delay of approximately two (2)minutes after turning the A/C on before the compressor starts and begins to put out cool air?
Is this normal?
Leah

David T. Richelderfer

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #1 on: July 07, 2015, 02:46:11 PM »
In my case I have three a/cs and they need to be delayed so that the load on the generator or shore power does not hit all at once (I think  lol).  FYI - I was told by the sales agent that turning the fan speed to low or high from auto will shorten/eliminate the delay time, but Mr. Simonis has stated otherwise.  Mr. Simonis stated the delay cannot be circumvented.

I realize it's impossible to turn on all the a/cs (either two or three of them) at one time.  But if they are all set to turn on and the generator or shore power is engaged, then they all would come to life concurrently... and that would create a problem of too much demand on the power supply (again, I think).

I noticed a few weeks ago that I cannot operate all the power demanding devices on my coach at one time.  I had all three a/cs on, the hydronic heater on, the insta-hot on, etc., and the demand on one leg exceeded 50 amps.  The demand was not much over 50 amps, only a few amps over, but it was enough to shutdown the generator with a one flash code.  Upon looking up the flash code it said low coolant.  I put in about 1/4th to 1/2 gallon to top it off, reduced the power demand by turning off the hydronic heater and unplugging the insta-hot, and the generator adequately supplied all three a/cs for the remaining two days.

« Last Edit: July 07, 2015, 02:56:03 PM by David T. Richelderfer »
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Fred Brooks

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #2 on: July 07, 2015, 03:44:54 PM »
             Hi Leah,

       What kind of air conditioners and thermostat do you have? Is the thermostat a Comfort Control 5 button made by Duo-Therm? Please advise and I will share some inherent flaws in their operation.
                             Regards Fred
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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #3 on: July 07, 2015, 04:36:25 PM »
Leah, if you have dometic air and have the newer digital thermostat and control box, this is the way it is setup. I have the delay on my front air, but my rear ac has the older thermostat and starts up with no delay.
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Chuck Jackson

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #4 on: July 07, 2015, 07:05:24 PM »
Mine does the same thing. This is normal. There is typically a short delay to keep the a/c compressor from short cycling. If the a/c was turned off and then on again (immediate) the compressor would be energized causing an excessive amount of electricity to start it and possibly causing a breaker to trip.

Just found this in the manual...

NOTE:
The compressor will engage
approximately two minutes after blower
motor activation to prevent accidental
compressor operation against high
pressure.
« Last Edit: July 07, 2015, 07:07:20 PM by Chuck Jackson »
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Joel Ashley

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #5 on: July 07, 2015, 08:10:55 PM »
I will hazard a guess that there are several protective reasons. 

One being that all motors draw more current at startup than after they get going and have momentum, kind of like your vehicle using more fuel from a dead stop than from a rolling start.  There are two motors involved, compressor and fan.  A delay would allow one motor to get beyond that startup current load before the other kicks on with its load.

Second, the system takes awhile to actually get refrigerant moving and begin exchanging heat so cooled air is available. 

And if it's like furnaces, there may be a sail switch in the fan's air path;  the system won't blow exchanged air until there is enough flow over that switch to verify adequate air speed for proper operation.

Any or all of those could be why there is a built-in delay.

Joel
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Edward Buker

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #6 on: July 07, 2015, 08:14:07 PM »
Once the compressor kicks on the "high side" pressure can reach several hundred psi depending on the air temperature and the specific gas used. Over time when the compressor shuts off, the high and low side pressure will go back to equilibrium pressure through a  small orifice or valve, to maybe 70 lbs. The delay is built in to not have the compressor try and start against that high side pressure, the designed in delay is just enough time to get the system to a pressure level where the compressor can safely start.

Later Ed
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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #7 on: July 08, 2015, 12:02:22 AM »
Was coloring grout on the RV interior today and it got hot and humid so turned the ACs on and noticed that the new T'stat http://beaveramb.org/forum/index.php/topic,4671.0.html I installed doesn't have any delays built in. #1 starts almost immediately and #2 about 5 seconds later. Only idea I came up with is to install a couple of time delay relays on the compressor signals; maybe 60 sec for #1  and 180 sec or so for #2. Anyone have other solutions in mind?, Also, can someone with basement ACs tell me what the delay times are on their units?
Thx, Steve
« Last Edit: July 08, 2015, 12:04:48 AM by Steve Huber Co-Admin »
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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #8 on: July 08, 2015, 12:41:36 AM »
Is this your thermostat made by RVProducts/Airxcel?

http://www.rvcomfort.com/pdf_documents/6536335_thermostat.pdf

Towards the bottom it says..."There is also a 3 minute anti-short cycle delay time for cooling"
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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #9 on: July 08, 2015, 01:03:20 AM »
Chuck,
Yes I noticed that but it doesn't seem to be functioning that way. Will check wiring tomorrow AM when cooler (no pun intended). I also verified the compressors each have overload protection circuitry but not sure this will address the timing issue.
Thx!  Steve
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Dick Simonis

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #10 on: July 08, 2015, 01:51:31 AM »
Steve, my AC has a 3 minute (?) delay on initial startup but after that none.  Personally, I wouldn't worry about it...nor will I since I'm in the process of installing that T-Stat.  The delay between repetitive starting is a safety feature that prevents short cycling.  With that said, there should be a short delay before the 2nd compressor kicks on that I suspect is more to even out the starting current loads.

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #11 on: July 08, 2015, 02:38:11 AM »
Dick,
Thx for the info. Let me know how yours is operating once you have it completely installed.
Steve
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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #12 on: July 08, 2015, 09:25:36 PM »
Checked operation on my t'stat / basement ACs this AM. #1 start up is effectively immediate if set point is below ambient. #2 will start w/in 3 seconds or so if set point is ~3 degrees below ambient. The t'stat has a 3 minute delay built in that delays a restart after AC has shut down. Seems only concern then is possible overload when starting both units at effectively same time in hot summer.
Steve
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Edward Buker

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #13 on: July 08, 2015, 11:38:53 PM »
Steve,

Should work out, you will learn how to deal with any short comings with this Tstat operation over time, and how to best set it up. What is probably most critical would be to simulate a few seconds of power outage while you might be away from the RV.

Have both compressors on, electric heating element also, which would probably be the usual. Flip the 50 amp breaker off, wait a few seconds and flip it back on and see what happens on start up. 3 minute delay? Both Start together or 3 seconds apart? Struggling at all on start up?

I would simulate the same thing on 30 amps with whatever settings you use for 30 amps and see if you can be be sure that only one compressor is all that gets enabled. If the new Tstat handles those situations then it would seem that the system under normal conditions would be good to go...

Later Ed
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LEAH DRAPER

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Re: AIR CONDITIONER DELAY IN STARTING
« Reply #14 on: July 09, 2015, 04:49:26 PM »
Fred
My two A/c's are Dometic with the Duo-therm thermostat The front A/C seems to take longer to turn on (i.e. 2mins) the rear seem a shorter delay (haven't timed it.) 

From the answers thus far I guess this is the "norm".

Sorry for the delay in responding but yesterday was a busy day.

Leah