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Old 12-04-2018, 12:35 PM   #1
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Rooftop Heat Pump/AC

My rooftop heat pump/ac will not power up unless I start the engine. There is no voltage to the bottom row of the whit rodgers coil I checked all on board fuses When I start the engine then I get power to the lower half. I tried using the generator ,no power also with it plugged into outlet (shore power) I noticed this after I tried to run it while plugged in to shore power and that caused my breaker to blow in the house I reset the breaker , now It will not work
I must be missing a fuse or ????


Any help will be greatly appreciated

Dean
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Old 12-04-2018, 01:23 PM   #2
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Quote:
Originally Posted by DMareno652 View Post
My rooftop heat pump/ac will not power up unless I start the engine. There is no voltage to the bottom row of the whit rodgers coil I checked all on board fuses When I start the engine then I get power to the lower half. I tried using the generator ,no power also with it plugged into outlet (shore power) I noticed this after I tried to run it while plugged in to shore power and that caused my breaker to blow in the house I reset the breaker , now It will not work
I must be missing a fuse or ????


Any help will be greatly appreciated

Dean

The only thing that comes to mind is turn the ignition key to the on position and try it then. It dosent square but I would want to know of the wiring for the AC low voltage is taken from the ignition wire instead of the battery wire from the ignition switch. Running the roof A/C units should not cause the breaker to trip unless there is something wrong with the A/C like a bad condenser fan or compressor.

Please keep us posted as I am just trying to give you a path, this one looks like a stumper. Unless my old brane is not working at all any more which is entirely possible.
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Old 12-04-2018, 01:57 PM   #3
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Originally Posted by DMareno652 View Post
...I checked all on board fuses When I start the engine then I get power to the lower half.
Does this mean that you also checked the circuit breakers for the AC units? If not, try cycling them off/on.

TJ
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Old 12-05-2018, 05:19 PM   #4
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Update

Yes the breakers in the coach were set
I went to the inverter converter I found a 25 A reset
It did not looked tripped put I pressed it anyway I also found fuses on the transfer system I tested them and also pushed them in to be sure full contact was archived
I tried the fan only while the coach was not running and they came on ( they did not earlier)
Today I decided to try heat pumps without the coach running or keys turned on
They came on and ran shortly then the house breaker ( 20 ) amp located 100 ft from coach tripped
I reset and just turned on one heat pump
It has been functioning for the last 3 hrs
It is 32 degrees here on Long Island

I am guessing that possibly a loose connection
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Old 12-06-2018, 04:34 AM   #5
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Have you ruled out transfer switch?
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Old 12-06-2018, 05:01 AM   #6
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You mentioned your house 20 A breaker tripped 100 ft from the coach. You can not run two heat pumps on a 20 A breaker. Also, heat pumps don't work well at 32 degrees.
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Old 12-06-2018, 08:54 PM   #7
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I agree with Paul...

20A...especially 20A running thru a 100 foot extension cord, isn't sufficient. That 20A isn't just being used by the air conditioner. The battery charger and other residual loads are present. If your coach has the PCS power control system...it will default to 30A when plugged into 20A. You have to manually select the 20A position. That will assist in cutting back the converter/charger...if installed.

When you reapply power to the unit...there is a timer built-in as well. This allows the refrigerant pressure to equalize before attempting to start the compressor. Some use a 5min delay.

There is a significant spike in amps when starting a compressor. You either have to have enough power availble...or you can lessen the spike by installing a MicroAir Easy Start.

Running the engine can't really do anything unless the BIM relay has closed, and is using Alternator output to charge the chassis batteries, allowing the converter to cut back the draw on the less than optimal 20A shore source. It might give you just barely enough to run one air conditioner.

If you start the generator...does the Air Conditioner work properly? If so...it's probably not the air conditioner giving you the problem...it's insufficient shore power availability. To run both units...you need 50A shore power...or 30A without the charger and other loads drawing power...or easy starts on both units. 20A...just isn't likely to power both. It will either shed one, if you have the PCS set properly, or trip a breaker.
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Old 12-07-2018, 04:57 AM   #8
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20 amp power is insufficient for an air conditioner in most instances. Once the outside temperatures get into the low 30's, they become pretty much ineffective.
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Old 12-07-2018, 05:40 AM   #9
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When you were having the issue of it only working when engine was running, it was because your battery was dead, or off, and the converter wasn't sending 12 volts to the thermostat system. That's what they run on, not the 120 volts that make the AC/heat pump run.

Starting the engine connected the chassis battery to the house battery thru the isolation/charging relay. Then you had power to the 12 volt devices.

Once you found the tripped converter breaker and reset it, the converter was working hard to charge the battery back up. That extra energy and the heat pump were to much for the house circuit breaker.

Heavier, shorter extension cord could help and once the battery is charged, the power needed for the converter will be less.
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Old 12-07-2018, 06:04 AM   #10
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When you were having the issue of it only working when engine was running, it was because your battery was dead, or off, and the converter wasn't sending 12 volts to the thermostat system. That's what they run on, not the 120 volts that make the AC/heat pump run.

Starting the engine connected the chassis battery to the house battery thru the isolation/charging relay. Then you had power to the 12 volt devices.

Once you found the tripped converter breaker and reset it, the converter was working hard to charge the battery back up. That extra energy and the heat pump were to much for the house circuit breaker.

Heavier, shorter extension cord could help and once the battery is charged, the power needed for the converter will be less.
^^^^^------^^^^^
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Old 12-07-2018, 06:38 AM   #11
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20 amps is plenty to run ONE rooftop AC/heat pump, BUT not much else can be running, and certainly nothing else that's high draw (and some of those are sneaky).
Certainly you can't run both heat pumps at the same time on just 20 amps.
At 32 degrees the heat pumps aren't really making much heat, if any at all. 40 degrees or so is about the point where they will either quit trying to make heat, or just can't do it because there's not enough warmth in the air.
At some point you'll need to either winterize (if you haven't already) or switch to some other heat source.
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Old 12-07-2018, 07:22 AM   #12
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20 amps is plenty to run ONE rooftop AC/heat pump, BUT not much else can be running, and certainly nothing else that's high draw (and some of those are sneaky).
Certainly you can't run both heat pumps at the same time on just 20 amps.
At 32 degrees the heat pumps aren't really making much heat, if any at all. 40 degrees or so is about the point where they will either quit trying to make heat, or just can't do it because there's not enough warmth in the air.
At some point you'll need to either winterize (if you haven't already) or switch to some other heat source.
.............Not really true - Few factoids

Heat pumps are tremendously efficient, even in cold weather. True, the efficiency does decline slightly as the temperature goes down, but even at very cold, single digit temps, heat pump efficiency is impressive and always better than any other setting on your thermostat.

The heat pump (In most RV's) is effective by itself down to temperatures around 25 to 30 degrees Fahrenheit.

As the ambient air temperature goes down, it is more difficult to extract heat, and the unit must work harder. ... Historically, below 20 degrees, air-source heat pumps drop in efficiency to 100 percent (no better that electric radiant heat). They do not drop below 100 percent efficiency.

Because they move heat rather than generate heat, heat pumps can provide up to four times the amount of energy they consume in electricity, according to the U.S. Department of Energy. Depending on the climate, air-source heat pumps are about 1.5 to 3 times more efficient than electric resistance heating alone


Many of the Newer Higher Efficiency Heat Pumps (SEER 18+) are efficient at even 0 degrees!


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As you can see I'm a Heat Pump Fan
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Old 12-07-2018, 07:45 AM   #13
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I was running the HP;s in mine before storage and when it got too cold they would not work and after it got warm(above freezing) by turning them on and off they worked again..
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Old 12-07-2018, 08:33 AM   #14
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.............Not really true - Few factoids
The heat pump (In most RV's) is effective by itself down to temperatures around 25 to 30 degrees Fahrenheit.

A Dometic rooftop unit, by design, transfers from heat pump to "aux heat" at approximately 35 degrees. Aux heat is usually a furnace or aquahot etc. The rooftop ambient sensor is not precise ... mine transfer at about 34 degrees. At 34, the heat pumps are not very effective due to the extended defrost cycles.
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