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Aquahot Engine Preheat


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I had to do some research to confirm my understanding of the normal “freebie” heating of the AquaHot while driving versus the Preheat function.

The Aqua-Hot's engine preheater function will not heat the coach. The Aqua-Hot 450D has a Motoraide feature that allows hot engine coolant to circulate from the engine to a heating coil inside the Aqua-Hot's boiler. This gives your heating system some free heat while driving. However, this circulation occurs naturally because the engine's water pump provides the flow. There's nothing you need to so.

The Engine Preheat switch utilizes that same coolant loop from the engine to the boiler but it operates in reverse and is designed for when you are parked and the engine is not running. In this case the preheat switch turns on a small circulating pump on the boiler that heats the engine coolant and sends it back to the engine to warm it up for cold weather starts.

Leaving the switch while driving is counter-productive because it will hamper the ability of the engine's water pump to provide heat to the 

OK….The above confirms what I thought as well as experience and reading the manual.  So, based on that and the comments.  And you may know this and it is in your manual.

the Preheat switch on the control panel has to be ON.  You have to have a source of heat for the boiler….either the electric or the diesel burner.  The ratio of electric to diesel, on MY 450 is 1:10 or 5.6 KBTU for electric compared to 56 KBTU for diesel.

You should hear the stir pump whirring, just like when you heat domestic hot water. I don’t know exactly when the Preheat Pump Light will come on, but that is what circulates the coolant back to the block.  When you drive, the engine water pump does the circulation.  

Again, this is generic.  I thought some of the pumps had a check valve in them and we had many member’s comments about the valve sticking and having to tap or physical “unstick” the valve for the pump to work.  Memory says that the pump light was on, but no circulation or flow from the pump.  But…I would call AH to verify what type of pump and check valve arrangement you have.

from the manual…..

Troubleshoot the Engine Preheat Pump if the following con- dition has occurred:
 The Engine Preheat Pump is not operating, and the Engine Preheat Switch on the Switch Panel inside the motor Home is in the ON position and the “Low Temp
Cutoff Status” indicator light is illuminated on the electronic controller.
 The Engine Preheat Pump indicator light illuminates red on the electronic controller

The manual (450) gas three separate references to preheat. One dealing with the interior switch and the “status”,conditions; the next is troubleshooting the Preheat from a mechanical as well as reading and understanding the lights; finally, the third is testing the control board for issues there.

hope this helps.  Give us feedback as the preheat is not discussed much here…

 

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Clarification:

we are in Indiana it’s 20° to 45° today.

the Aquahot is on its 65° inside both the diesel and electric elements are in use all functioning as they should.

Before attempting to start a cold engine the switch in the cockpit “engine preheat” is turned on and the switch does not light. 
exit the coach check the control panel and the light on that labeled Preheat also is not lit ! The stir pump does not activate as described above 

The block heater is a separate switch on the dashboard and it’s not plugged in in the engine compartment at this time. 
 

 

Edited by Wheelsnkeels
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It won't be a fuse if everything else on you Aqua Hot is working. The LED board sends the 12 volts up to the Engine preheat switch all the time and when the switch is on the 12 volts is sent back to the LED board. This will turn on the FET transistor, which will turn on the engine preheat light and the engine preheat pump under certain conditions. The preheat LED and Pump won't come on unless the low temp cut off LED is lighted. And most units are set up to not turn on unless the diesel switch is also on. 

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You Do NOT want the engine preheat on when the engine is RUNNING. The engine water pump and the AQ pump are fighting each other. 

On 12/2/2022 at 7:57 AM, Tom Cherry said:

I had to do some research to confirm my understanding of the normal “freebie” heating of the AquaHot while driving versus the Preheat function.

The Aqua-Hot's engine preheater function will not heat the coach. The Aqua-Hot 450D has a Motoraide feature that allows hot engine coolant to circulate from the engine to a heating coil inside the Aqua-Hot's boiler. This gives your heating system some free heat while driving. However, this circulation occurs naturally because the engine's water pump provides the flow. There's nothing you need to so.

The Engine Preheat switch utilizes that same coolant loop from the engine to the boiler but it operates in reverse and is designed for when you are parked and the engine is not running. In this case the preheat switch turns on a small circulating pump on the boiler that heats the engine coolant and sends it back to the engine to warm it up for cold weather starts.

Leaving the switch while driving is counter-productive because it will hamper the ability of the engine's water pump to provide heat to the 

OK….The above confirms what I thought as well as experience and reading the manual.  So, based on that and the comments.  And you may know this and it is in your manual.

the Preheat switch on the control panel has to be ON.  You have to have a source of heat for the boiler….either the electric or the diesel burner.  The ratio of electric to diesel, on MY 450 is 1:10 or 5.6 KBTU for electric compared to 56 KBTU for diesel.

You should hear the stir pump whirring, just like when you heat domestic hot water. I don’t know exactly when the Preheat Pump Light will come on, but that is what circulates the coolant back to the block.  When you drive, the engine water pump does the circulation.  

Again, this is generic.  I thought some of the pumps had a check valve in them and we had many member’s comments about the valve sticking and having to tap or physical “unstick” the valve for the pump to work.  Memory says that the pump light was on, but no circulation or flow from the pump.  But…I would call AH to verify what type of pump and check valve arrangement you have.

from the manual…..

Troubleshoot the Engine Preheat Pump if the following con- dition has occurred:
 The Engine Preheat Pump is not operating, and the Engine Preheat Switch on the Switch Panel inside the motor Home is in the ON position and the “Low Temp
Cutoff Status” indicator light is illuminated on the electronic controller.
 The Engine Preheat Pump indicator light illuminates red on the electronic controller

The manual (450) gas three separate references to preheat. One dealing with the interior switch and the “status”,conditions; the next is troubleshooting the Preheat from a mechanical as well as reading and understanding the lights; finally, the third is testing the control board for issues there.

hope this helps.  Give us feedback as the preheat is not discussed much here…

 

SOME of that C&P is not very good.

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1 hour ago, 96 EVO said:

What's C&P ?

Copy and Paste.  I went back and edited to original post with the C&P (italics)……but  did not footnote the source….  Almost like writing a term paper….  LOL…  Hope this clarifies it…🤣


 

 

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10 minutes ago, Tom Cherry said:

Copy and Paste.  I went back and edited to original post with the C&P (italics)……but  did not footnote the source….  Almost like writing a term paper….  LOL…  Hope this clarifies it…🤣


 

 

Ok, I get it!

The section you copied Does suggest you don't run the pre-heat pump while the engine is running, it just doesn't say it in a very clear way!

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On 12/3/2022 at 1:58 PM, Paul A. said:

You Do NOT want the engine preheat on when the engine is RUNNING. The engine water pump and the AQ pump are fighting each other. 

Paul, good point.  You are absolutely correct.  On my coach, the Aquahot Preheat pump circulates engine coolant in the reverse direction compared to the engine water pump.

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17 hours ago, Wheelsnkeels said:

Ok went through the trouble shooting on the Aquahot service manual today and as it turns out it’s the switch that’s defective.

Bypassed with a jumper wire and it’s all good now to determine the correct matching replacement switch and replace it.

08DE39F6-F015-43EC-B5C4-A5094024FAF5.jpeg

Look up marine contura switches. This style rocker switch is used a lot in boats.

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High probability these are Carling Contura switches.  There are many versions of the switches.  All the switches are, basically the same, the difference is the actuator or the button on top.  If you pull out the switch or FIND THE PRINT for it, you can go to the Carling site and find a replacement,

NOW…the TRICK.  The actuators tend to “fail” as in they are what operates a small pin in the switch.  My exhaust brake switch actuator “broke”. I could still push down on it and then click it on  and off, but it was not “latched” or clicked into the housing.  Test and figure out if the switch is bad….or the body of the switch.  You may be able to salvage the plastic bonnet or actuator if it is good.  BUT….there is a special “Carling Switch Actuator Removal Tool” that you need.  Google them.  Amazon has them.  You run a HIGH CHANCE of damaging the plastic actuator.  I am 2 for 3 on removal…and I will NOT take one off without having the tool.

I called Carling and they identified my “curved” contura actuator.  So, I ordered a blank one.  I made a label from a Brother label machine and it looks nice.  The issues is NOT finding a Carling Switch….they are readily Available if you have the PN or specs or circuit.  BUT, the Actuators were pad printed in large batches for Monaco.  There is virtually no source.  You can find a myriad of actuators on eBay, but I never found an exact replacement.

I would HOPE your switch actuator is ok.  Obviously a Brake (exhaust/Jake) gets a LOT of cycling.  Mine was also a victim of SUNLIGHT.  I should cover the switch panel when in storage…..RED is a color that does not take direct UV well..

so….determine if it is the switch or the actuator.  If the switch is OK, then get a replacement actuator.  If the switch is bad, then a NEW switch.

I would add…..it MAY BE MONACO!!!  If there is a poorly crimped spade lug or a butt splice in the line, then your diagnosis may be flawed.  Pop out the switch.  Find the circuit and then jumper….and make the circuit as the switch was ON. You MAY have done that.  But check before you order or do a lot of major surgery.  Trust me on that one.  I know a lot of members that replaced switches, with great difficulty and found a downstream wiring or an open lead (poor butt splice). 

Good Luck.

 

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  • 2 weeks later...
On 12/2/2022 at 8:03 AM, Jdw12345 said:

Have you let it run on engine pre heat with a cold engine to see if it’s actually working correctly without the light on the control board being on?

Yes but it did not make a difference if you jumper the pins per the troubleshooting it lights and you hear the pump.

tested the switch and it’s actually good so somewhere there’s a fuse or broken wire?

the manuals show a fuse block on the Aquahot but it’s not on mine so Monaco put it somewhere else as they did with the preheat switch being on the console and not near the diesel and electric switches.

 

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On 12/2/2022 at 10:37 PM, On_the_road said:

On my AquaHot AHE-100-01S there is a fuse for the preheat pump.   In the picture, there is a fuse block just below the connection block in the upper right corner.   The fuse for the preheat pump is the left most fuse.   Each pump has a fuse in the fuse block.

DSC03007.JPG

You have a fuse because you have the classic 3 relay system . If you have a electronic LED control board the pumps are controlled by FET and have auto reset fuses soldered to the circuit board upstream from the FET,s

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Sure would help to know exactly what model Aqua-Hot you have.

I am familiar with models 100-01, 431/12 that were/are in my Windsor and the now the 100-04 that is in my Dynasty.

The first two have fuses on the inside of the Aqua-Hot just above a set of old fashion relays as depicted in a previous photo. The 100-04 has a separate control panel with LED's that light up.

Haven't had time to completely go through the 100-04 as yet to understand it's system but taking it one step at a time. Right now it's working as it should, so I am still in the learning phase.

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Some of the dash switches light up when turned on and some don’t but they all function ok. I know I turned on the Aqua Hot preheat on one cold morning and had to turn on the Aladdin and watched the engine temperature slowly rise to make sure it was working. 
Ricjard I am getting ready to service my Aqua hot for the first time I have the same unit you do so I will let you know how it goes

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12 minutes ago, Georgia Mike said:

Some of the dash switches light up when turned on and some don’t but they all function ok. I know I turned on the Aqua Hot preheat on one cold morning and had to turn on the Aladdin and watched the engine temperature slowly rise to make sure it was working. 
Ricjard I am getting ready to service my Aqua hot for the first time I have the same unit you do so I will let you know how it goes

Your AH may be different so I would read the manual.  For example, diesel light came on.  However, the nozzle was plugged or “crudded over with the normal varnish” as the tech put it.  It would not ignite or burn.  After say 5 minutes, the Diesel AH light went out.  That was a fault code.  Diesel did not ignite. My comment….review and make sure that a faulty lamp is fixed as it may tell you a fault or trouble code. If the book says it will come on, then make sure that is not a sign of a board fault and replace the switch or the indicator.  Your VOM will tell you if you have power to the switch indicator lamp.

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