BAC Forum
General Boards => Technical Support => Topic started by: LEAH DRAPER on July 07, 2015, 02:36:05 PM
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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
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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.
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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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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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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.
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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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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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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
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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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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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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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Dick,
Thx for the info. Let me know how yours is operating once you have it completely installed.
Steve
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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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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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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
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Hi Leah,
No problem because we all know life happens..........If the comfort control t-stat is the 5 button (which is obsolete) style, The delay is approx 2 minutes if the t-stat is in AUTO mode. What they don't tell you is if you touch any other button once you have turned it on, you add another 30 seconds delay on top of the two minutes. So if you turned it on and tapped the temp up or down 6 or 8 times you can add 4 more minutes to the delay. No problem, Just turn the t-stat off and back on. If you want to by-pass the initial delay, move the fan switch off of "Auto" to hi med or low and fans will come on right away. The compressor will still have 120 second delay before engaging.
Temperature differential between output cooled air should be 20 to 26 degrees cooler than return air going into the air conditioner. This temperature variable is based on how much humidy is in the air. The higher the humidy the heavy the air is which makes it harder to cool.
Hope this helps, Fred
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If the comfort control t-stat is the 5 button (which is obsolete) style....
Fred,
Given that my Tstat is the 4 button, which I have kept alive by cleaning the contacts with QTip and alcohol, it must really be obsolete. I thought the 5 Button was the upgrade. Is there now a TStat to replace what I have? This TStat listens to no less then 2 other sensors (bathroom, and bedroom), as the 5 Button does, I guess.
Thanks,
Mike
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Hi Mike,
The 4 button was replaced by the 5 button, The 5 button was replaced by the 12 button. If you are going to entertain doing the upgrade here are some considerations. If your coach has the 4 button that means your air conditioners are over 12 years old or more. Life expectancy of the A/C is 10 to 15 years. If you change from the 4 button to the 12 button you will have change printed circuit control board inside EACH air conditioner and rewire some of the wiring at that board. I'm not sure spending the 250 to 300 parts and labor (not including the price of the 12 button t-stat) on each air conditioner is a wise decision. I've done this upgrade over 12 times only to have the air conditioner expire within a year or two.
Hope this helps, Regards, Fred
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Fred,
I have the 5 button thermostats and have not had a problem, but if I did, what is involved with going from the 5 button to the 12?
Later Ed
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Hi Ed,
If it ain't broke, don't fix it. LOL The 5 button is a pretty dependable t-stat. If your going to make the change, the same things apply as my previous post. I think the only 2 things that will not work if you go to the 12 button is the de-humidify option and the outside temperature option.
Regards and I enjoy your posts and info, Fred
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Fred,
No plan to fix it until it is broke..... Our 2002 Marquis has two rooftop airs which was an option over the basement air for that year. Luckily the original owner chose that option, just think that system is more easily repaired with replacement units. I do see Adventure RV and several other sources of 5 button thermostats out there so I guess one could handle a thermostat replacement for now with available parts. If they are being obsoleted maybe I should buy a spare.
I also enjoy your posts and your broad knowledge and hands on background in so many aspects of RV work...glad you bought a Beaver and joined our forum :-)
Later Ed
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Thanks Ed,
Here is probably the way the scenerio will play out seeing your air conditioners are 14 years old. One of the air conditioners will fail either by loss of freon or compressor lock-up or who knows what......When you go to get it replaced, they will advise that the replacement A/C will not communicate with the 5 button T-stat. They will advise that you purchase the 12 button t-stat and the upgrade the PC board for the other A/C that is working ok or they will say why not change both air conditioners and be done with it. Not the story you want to hear but unfortunately that is what will happen, start saving your pennies or if your in Tucson come and visit me. Incidently the 12 button t-stat is a horizonal mount, not sure where yours is located.
Regards, Fred
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Just replaced the rear unit on my 99Marquis. The unit works well with the 4 button thermostat that is there......in August I will replace the front unit with a new unit as well. The difference between the old unit and the new is phenomenal. The rear has never been that cold since we owned the coach.
There is a guy who rebuilds 4 and 5 button thermostats on eBay. Very reasonable and mine has worked for over 4 years with no issues.
Great info Fred enjoy reading your posts.
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Just replaced the rear unit on my 99Marquis. The unit works well with the 4 button thermostat that is there......in August I will replace the front unit with a new unit as well. The difference between the old unit and the new is phenomenal. The rear has never been that cold since we owned the coach.
There is a guy who rebuilds 4 and 5 button thermostats on eBay. Very reasonable and mine has worked for over 4 years with no issues.
Great info Fred enjoy reading your posts.
Tom, what A/c did you buy for your replacement. I have one that is super loud and may replace it soon. Thanks!
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Tom, Do you have a 4 button t-stat for each air conditioner?.......Fred
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Lamonte, I called Dometic and they said the unit that is a direct replacement for mine is 640315CXX10 Model 60184. Bought at camping world for $680.00
Fred, my 4 button has 3 zones and yes it operates both units.
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There is a guy who rebuilds 4 and 5 button thermostats on eBay. Very reasonable and mine has worked for over 4 years with no issues.
Tom and all with 4 Button Tstats or '99 Marquis,
I was all ready to send my 4 button to this guy on Ebay, but figured it clean the contacts first because another online poster recommended it could be done.
I removed the unit by unscrewing from the wall and disconnecting the cable, opened it up, and used a QTip with alcohol on the locations where the switch contacts were under each button. I felt as I was doing this that, "there is no way this is going to work". I even got part numbers of the contact switches, or attempted to, so that I could see what new ones cost - no luck there.
So I wondered how this Ebay guy was "fixing" these things. After returning the unit to the coach, and feeling like I'd done nothing, the unit worked like a champ. My only guess is that over the years we keep pushing those buttons with dirty fingers and eventually create the problem, which is cleaned up with simple Qtip and alcohol, so I would suggest rather than sending your unit to the ebay guy along with $100 I think it is, that you try cleaning it, then try keeping your hands clean while using it. Mine's working fine now even after a year since I did the cleaning...not perfect but it was awful before the cleaning in that I couldn't get anything to happen using the buttons to turn the temp up or down. Now, sometimes, I might bounce a couple degrees, but its responsive.
Anyway, just my experience. I can not imagine that this guy for $100 can refurb these units, but I bet he has a better cleaning operation than I used, and that's all he does.
So far, Tom, my '99 is cooling well both units, at least according to my wife. We only run it to about 73 or 74 degrees, so for now all is well. This coach of mine I am happy to say just doesn't seem to have been pushed that hard in the 65,000 miles or so before I purchased it, and has spend most of its life (until I purchased it 9/4/13) inside. Now I store it under cover but it isn't inside any longer, so I guess its beginning to wear a bit more.
I'll close by knocking on wood. :)
Mike
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Tom, Do you have a 4 button t-stat for each air conditioner?.......Fred
Fred, the '99 Marquis have the 2 roof airs with temp sensors only in the bedroom, and bathroom, and also one for the living room within the single 4 button tstat which allows you to program each ZONE (up to 4, only 3 are used). I don't see how the cooling is different since we only have 1 air for both bathroom and bedroom, but the heating is definitely independent in all 3 zones.
Mike
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I was somewhat taken aback when I removed the wood panel to expose the rear unit. I thought the bedroom and bathroom were on the same unit, however, the bathroom is cooled by the front unit.
Once the panel was down it was an easy job. I spoke to Dometic and they told me the new unit would work with the old control box for the 4 button thermostat.
When I had issues with the old 4 button I bought new control boxes and a new 5 button just in case it failed. If it does I am ready with the upgrade to the five button.
The amount of air the new unit pushes and quick cool down it was worth the effort. That's why I will go ahead and replace the front later in August.
The new unit cools dramatically better going down the road versus the old units.
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Mike, The sensor (thermister) in the bathroom is for the aquahot I believe and has no effect on cooling. The front A/C is the master and the t-stat and aquahot are connected to that unit. The rear A/C is daisy chained thru a comm line (looks like a phone line) to the front A/C. Inside each A/C from the top side is a pc control board. This pc board has 8 dip switches for various options: ie zone 2,3,4 furnace, ect. Your rear A/C has the zone 2 dip switch turned on so the t-stat knows it has 2 air conditioners connected to it. The front A/C has the furnace dip switch turned on so the t-stat knows it has a furnace or aqua hot connected to it. The original 4- button t-stat required that you hold down the top 2 buttons at the same time for a second to toggle between zone 1 and zone 2 as indicated in the led display towards the bottom of the t-stat window.
Question, When you use the aquahot in the barhroom, does the t-stat show zone 3?
Regards, Fred
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WOW, am I getting an education from all my fellow beaver owners. I had no idea that the Dometic 640315cxx10 would communicate with a 15 year old 4-button t-stat. You guys are pretty creative taking stuff apart and cleaning the top two buttons were most customers start looking for a replacement t-stat.
This only proves you guys are the best educated and knowledgable I have ever communicated with that own this level of luxury coaches. Kudos to BEAVER owners...........Fred
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Fred, with a 16 year old coach you have to be resourceful. Or you end up broke, not the coach.
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Question, When you use the aquahot in the barhroom, does the t-stat show zone 3?
Regards, Fred
Fred,
My zones for the Oasis Combi, are the same as they were for the Hurricane which was standard. The 4 button has 4 zones indicating by backlit 1, 2, 3 (and I thought 4 but I could be wrong). Zone 1 is front, Zone 2 is rear, and Zone 3 is the bathroom as far as the Oasis combi heat is concerned. When ITR installed the combi, in Oct, 2013, they told me they "fixed" the zones so it went 1, 2, 3, from front of the coach to the rear, but I found out my bedroom thermistor was controlling the bathroom when I closed the bedroom door and the bathroom heat never shut off, so while they had changed the wire for the thermostat control, they failed to change over the other wire from the thermistor. Not knowing what the A/C was doing, as it shows 3 zones independently set for cooling, I just changed the thermistor wires back so that they now matched the control wires.
Anyway what Tom is saying really is not true in my '99 Marquis, because I know that if I set my cool for Zone 3 (bathroom), the rear A/C unit comes on, same for Zone 2, the bedroom. Unless, its just the fan in the rear unit that comes on, sucking air from the front unit when the bathroom calls for cool. Is that what you found, Tom? I can check, but I don't think my front unit comes on, if the bathroom calls for A/C. I'll check next weekend when I go back to storage.
Mike
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Hi Mike,
To the best of my recolection of all the manufacturers (country coach, monaco, safari, newmar and Beaver) that were using that system with an aqua hot or hurricane, zone 3 was the most confusing to the owners when the coaches were new. The way they were originally configured was when you toggled the t-stat into zone 3, it would show "cool, fan, furnace, ect" when scrolling thru the mode button. In reality the only thing that functioned was the furnace. Customers would ask why is there nothing happening when I ask for "cooling" in zone 3. I would try and explain that zone 3 is only for heating in the lavy. Well over the years, a lot of technicians and owners have gotten creative trying to figure this out and modified the configuration to get zone 3 to do stuff. I'm not real sure exactly how yours is working, but it sounds like you have control to get the desired result. Hope this helps.
Regards, Fred
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Fred,
Well, I guess I need to see if setting the cool in Zone 3 (lav) controls Zone 2 (bedroom) cool. If that's true then I don't have to worry about setting both when I want to change 1. At least you've seemed to confirm that Zone 3 is a standard meaning lavatory for heat as I'd thought somebody just made a mistake in the wiring.
Next weekend I'll be running the generator for a couple of hours and as I do I'll leave Zones 1 and 2 off, and turn on Zone 3 cool and see what happens, then test each independently. That will tell me whether Zones 2 and 3 are OR conditions or Zone 2 does nothing at all to turn on the air conditioning.
Thanks,
Mike
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My coach has three controllable heating and cooling zones, plus a fourth zone (the basement) that is not readily controllable. On my coach zone 1 is the living room, zone 2 is the bathroom and zone 3 is the bedroom. There are two 5-button thermostats, one in the living room for the living room, and one in the bedroom selectable for the zone 2 (bathroom) and zone 3 (bedroom). Zones 2 and 3 have their own a/c - heat pump, and heating furnace.. The bottom button on the bedroom thermostat is switchable between zones 2 and 3. The thermostats operate all devices for heating and cooling, except the squirrel cage fan speed for the furnace heating devices located near the floor in all three zones, not to be confused with the overhead fans associated with the a/c-heat pumps. The thermostats control the a/c - heat pumps and their overhead fan speeds, and the furnace, but will allow only one function to operate at any one time - those being either a/c, heat pumps xor furnace. That is, if one function is turned on, then the other two functions are automatically off.
When the bedroom thermostat is set to zone 2, for example, I have control of the bathroom a/c-heat pump and the bathroom heating furnace. When it is selected to zone 3, then I have control of the bedroom a/c - heat pump and the bedroom heating furnace. Also, the a/cs blow into a common duct that goes from just behind the pilot/co-pilot's seats all the way back to almost the bedroom wardroom closet. All three a/cs - heat pumps will push cooled or heated air, respectively, to all three zones. But most air exits the common duct near the operating device. At night in hot weather and if I want cooling without the noise in the bedroom, then I turn on the living room xor bathroom a/cs and leave the pocket doors open. Much of the cooled air makes its way to the bedroom via the common duct.
In summary, I have three zones, each with its own devices, and each zone is selectable from one of two thermostats. I find it a very simple system to operate. If you want heat and it's above 35F or so, then turn on the heat pumps, one or two or three of them. If you want heat and it's below 35F or so, then turn on the furnace heating, either one zone or two zones or three zones. If you want cooling, then turn on the air conditioning, either one, two or all three air conditioners. Very simple.
The only issue I have had to deal with is if all three a/cs are on, then two of them are pulling power from a common leg. If the microwave aor the electric water heating element aor the insta-hot are on, then that heavily used leg will exceed 50 amps of power draw.
"xor" means exclusive/or. "aor" means inclusive/exclusive or.
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Hi David,
Your coach has the Monaco Signature configuration which in my opinion is the most straight forward system engineered at that time. As far as trying to balance the electrical load, it requires management as you have figured out. Monaco put 2 of airs on one leg and the 2500 watt converter/inverter and the other air on the other leg. The rest is a balancing act dependent on usage. Glad you have a grip and all systems work as designed.
Regards, Fred
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Fred and Tom,
I like the idea of replacing air units and being able to use the same 4/5 button thermostat system, nice option. Originally my roof air covers were not painted to match the coach so I primed, painted, and clear coated the covers to match the coach. To me that is an issue, Tom did the new air units and the old ones have the same cover configuration and do you think one could put the old covers on the new unit? Fred, thought you might know the answer also. My current units are the lower profile Dometic units that were used on most all the coaches. Hate to have to paint new covers, it is time consuming and not my favorite chore.
Later Ed
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Hi Ed,
Low profile Duo-therm/Dometic units are called Penguin models an I believe the 2015 units are configured different than the originals. Fred
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Ed,
The Penguin covers come in white and ivory. I got 2 in ivory for the Contessa and they were actually a tan color that matched the coach much better than the original white covers. Might save you a paint job.
Steve
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Steve and Fred,
Thanks for the info, will see how close the color is if I have to go through this change.....hopefully I will get lucky.
Later Ed
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On mine they were painted to match the coach, the new ones are white. Fine with me, as I had to replace the satellite dome and it was white. The old covers do not work with the new unit.