Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 10, 2025 ...

HWH compressor control

November 25, 2020, 02:43:38 pm

When we picked up our coach it had a owner added shutoff switch added on the HWH compressor and was and is off. Has been off ever since we have owned. HWH computer is removed and sent out for repair. Internally shorted. So while installing storage batteries I heard a relay lock in. Isolated to HWH compressor. Coach completely shut down. Switch was installed on motor power wire so it was not running but does if it is on. Wire diagram  I have with coach does not show anything but power and ground wire. Other wire about 20 gauge going to compressor marked 9700 makes no difference if disconnected. Compressor will cycle off once it reaches cut out pressure. I can't imagine this is normal to have it seeking pressure with coach powered down and disconnected from external power. Also if you disconnect the aux compressor solenoid wire that too makes no difference? Is there logic in the control on compressor? Relay drops out when power removed. Suspect someone prior wired wrong, but no print on compressor itself. Couldn't find anything on this in history. I feel this is really newbie question, but I am still. Power at cb removed for now. Hum maybe buss shouldn't be powered up? Fridge is also on that buss
Scott

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Re: HWH compressor control

Reply #1 – November 25, 2020, 02:48:13 pm

That is the hot coach battery buss. So it is hot with coach powered down
Scott

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Re: HWH compressor control

Reply #2 – November 25, 2020, 03:14:28 pm

Think I figured out what is going on. Found print on compressor connection diagram MP85.474E and suspect diode in detail A or something in that area. Should be able to figure out
Scott

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Re: HWH compressor control

Reply #3 – November 25, 2020, 06:27:28 pm

So my switched power thru the 60/90 psi pressure switch is connected to main power wire going to compressor solenoid directly making it hot all the time the coach has charged coach batteries seeking to run air compressor and never relaxing for storage. This seems to be wrong. I can understand you need to keep slide sealed but this is a always active system then. Anyone have any input. I will be putting the switch shown in the upper portion of the diagram for storage. Anyone who has put a switch in there power wires to shut down the compressor still has the relay energized as mine has been since built.
Scott

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Re: HWH compressor control

Reply #4 – November 26, 2020, 12:47:20 am

Just a thought, but our coach will start the compressor a few times a night to keep coach level. If you have the auto level turned on. Which requires it to have a hot wire to it at all times.

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Re: HWH compressor control

Reply #5 – November 26, 2020, 10:23:54 am

I'm not concerned in the least about having on the hot buss during use..

I'm concerned that all the people that have installed a power switch to shut the compressor off are unaware that the control relay is still active and once the air pressure drops the relay is energized the entire time in storage.

The switch needs to be in the wire to the pressure switch which controls the relay for the compressor.
Not the power wire to the compressor
This will prevent the relay from energizing and keep compressor from running

If the relay remains on it is drawing power the entire time from the coach batteries in storage. Disconnecting batteries will do the same thing Even better.
 Scott

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Re: HWH compressor control

Reply #6 – November 26, 2020, 10:45:50 am

Hopefully this will make sense. The switch (Red) is the diagram was not installed by Foretravel. They installed the power connection (purple) direct to hot coach battery buss. I'm saying HWH,s diagram is correct and should be followed. Previously my switch was placed in the green location and is wrong.
Scott

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Re: HWH compressor control

Reply #7 – November 26, 2020, 11:34:33 am

DSD,

This is another example of a picture worth a thousand words.  I was having a hard time following exactly what the situation was.  The diagram, with a few words of explanation, make it clear. 

Thanks,

Richard

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Re: HWH compressor control

Reply #8 – November 26, 2020, 03:38:50 pm

Scott, you are correct.  Just adding a switch to the power to the compressor doesn't prevent the pressure switch or the HWH system from clling for the compressor to come on and when they do the water trap solenoid it energized. So even with the power to the pump interrupted the solonoid is on and gets hot.

I have the same compressor wiring drawing but in my coach there was no solenoid in either line 57 to the leveling system nor in line 75 to the HWH tank.  The HWH compressor does not supply air to the Aux Air Hose Connection (line 5) or anything else.

As far as I here found there are three distinct air system variations for the 2001 U320.  The upper right corner of the title box on FT drawings shows the build number at which the drawing becomes effective.  FT did not revise drawings to show the end number when the drawing was superseded by the next revision.

I have since rewired and replumbed mine to be more like a 2003.

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