HWH Aux Air Compressor

[Gatesway]

The Thomas air compressor that keeps the HWH leveling system aired up is not working. There is power to the relay (behind the water separator in first photo) but there is no signal to open the relay to turn on the air compressor.

On the 2nd photo, I jumped the lugs (top one is power from the fuse box) and the compressor ran just fine. So, I'm not sure what to do now.

Any help would be appreciated!

Thanks!

[1doodadd]

Have you checked the HWH control board that sends the signal to the compressor making sure of the connection.

[Gatesway]

Originally Posted by 1doodadd

Have you checked the HWH control board that sends the signal to the compressor making sure of the connection.

No, I have no idea how to do that.

Great idea...but how?

[deandec]

I do not know for sure, but if you know the connection points, you could use a cheater cord and wire clamps to bypass the installed wire to see if the signal travels across the cheater wire.

[kenwyatt]

On mine the 12 vac is on the wire feeding the compressor All the time. A ground is supplied back at the board in the controller but there’s also a pressure switch on the compressor that can affect it. PM me I have some troubleshooting data.

[DJ55]

John, Foretravel used many of the same components back in the day, so I sometimes find helpful information on the allthingsforetravel.com site (which used to be named beamalarm.com). They used the same Thomas aux compressor setup, so this troubleshooting guide might give you some ideas about how to proceed (obviously, wire and fuse numbers will be different than ours).

[BrianGlenn]

Have you tried to raise Coach air springs with the HWH control panel and engine not running? With low air pressure in auxiliary system the HWH will call for the Thomas air compressor to provide air to raise Coach.

It provides air directly to air bags through the HWH “six pack” solenoids. It will not fill the auxiliary air system tanks or primary/secondary tanks for service/park brakes.

This is how my Thomas is wired and plumbed.

Brian

[Gatesway]

Dave, thanks for the link to foretravel.com! That helped a great deal.

Brian, I spent the day yesterday fixing a cracked fuel line to the Hurricane and did not work on the Thomas air compressor. I'll get to that hopefully soon. Thanks for the overview of how the thing is plumbed.

I'll post back when I have done some diagnostics.

By the way, Ken Wyatt shared this .pdf from HWH that some others may find helpful:

[rampage42]

You are correct, that is a pressure switch.
Check the relay you jumpered, ground the little terminal, the other side is 12+.
If does not start the compressor then relay is bad. If it closes then move on to next.
Check where the ground wire goes from that relay, I believe to the pressure switch.
One Side of the pressure switch should go to ground, check it, the other side will go to the relay.
Strip back a little bit of each wire on the pressure switch and touch them together. If the compressor starts then your pressure switch is bad.

[rampage42]

CORRECTION.
The relay is grounded do a jumper from the positive side of the relay power in to the one little terminal at the top, the non ground side.
If the relay clicks and compressor starts then go on to check the pressure switch.
Strip back a little insulation on each wire of the two coming out of the pressure switch and touch those together. If the compressor starts your pressure switch is bad.

[Gatesway]

Guys,

Well, I figured out what the problem was - after diagnosing (with your help) that there was no 12v coming from the HWH control module to the Thomas compressor, I decided to open up the module. After reading the HWH troubleshooting guide, I found the 9700 wire that travels to the compressor.

Turns out that the 9700 wire plug was in the wrong place on the control board! After testing where it should be (12v when raise arrow pushed on HWH panel) I moved the 9700 plug where it should go and viola, it is fixed.

Summary: Check and recheck how things should be wired - there are times when prior owners (or prior techs) don't necessarily put things where they should be! Don't assume anything!

Thank you all for your help! So, so grateful....

[DJ55]

Good going, John, thanks for your update. Glad it's fixed, and nice to see it didn't require another expensive shop or tech visit!

[azpete]

so this compressor has never worked since you purchased the coach?
it would have been nice for the previous owner to tell you that.

[kenwyatt]

Great troubleshooting! Job well done and it always give me a great feeling when I get something fixed myself and understand the equipment better.