Electro level down switch running pump

T

tyler

Active member
Jun 22, 2013
518
98
28
Started diagnosing the 78 air suspension system. Found a clear leak at connection to bag shut off valve. Also found a slow leak through one height
valve dump nozzle which I may have to clean/disassemble to see if usable.

Question: when I have the electric switches in hold, and hit the "down" buttons, they turn on the air pump, is that right or a sign of problem. (Up
button turns on pump and tries to go up, but weak original Dana pump and the above mentioned leak not very effective). With down switches, one side is
venting as expected and the other is not reliably activating the release solenoid, so something is not connecting right. But as I dig in, I don't know
if I am supposed to get the pump going up to pressure AND venting/exhaust (should be possible I think, a pressure side, and release from the bags).

I found this
http://bdub.net/gmcmotorhome.info/levelsch.htm
but i'm not picking out my answer as of yet
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
 
TYler'
It is normal to have the compressor run even when lowering the coach.
I'm not into it enough to expain why.

> Started diagnosing the 78 air suspension system. Found a clear leak at
> connection to bag shut off valve. Also found a slow leak through one height
> valve dump nozzle which I may have to clean/disassemble to see if usable.
>
> Question: when I have the electric switches in hold, and hit the "down"
> buttons, they turn on the air pump, is that right or a sign of problem. (Up
> button turns on pump and tries to go up, but weak original Dana pump and
> the above mentioned leak not very effective). With down switches, one side
> is
> venting as expected and the other is not reliably activating the release
> solenoid, so something is not connecting right. But as I dig in, I don't
> know
> if I am supposed to get the pump going up to pressure AND venting/exhaust
> (should be possible I think, a pressure side, and release from the bags).
>
> I found this
> http://bdub.net/gmcmotorhome.info/levelsch.htm
> but i'm not picking out my answer as of yet
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
> Started diagnosing the 78 air suspension system. Found a clear leak at connection to bag shut off valve. Also found a slow leak through one height
> valve dump nozzle which I may have to clean/disassemble to see if usable.
>
> Question: when I have the electric switches in hold, and hit the "down" buttons, they turn on the air pump, is that right or a sign of problem.
> (Up button turns on pump and tries to go up, but weak original Dana pump and the above mentioned leak not very effective). With down switches, one
> side is venting as expected and the other is not reliably activating the release solenoid, so something is not connecting right. But as I dig in, I
> don't know if I am supposed to get the pump going up to pressure AND venting/exhaust (should be possible I think, a pressure side, and release from
> the bags).
>
> I found this
> http://bdub.net/gmcmotorhome.info/levelsch.htm
> but i'm not picking out my answer as of yet

Do you have an electro level 1 or II system? Typically, a '78 is Electro Level II and has two pumps, one for each side with no air tank. I'm not sure
about how it operates but I do not believe the pumps will come on when lowering. Sounds like from your description, you have an Electro Level I. If
that is the case, then the one pump will come on when you press the lower buttons just as you describe - that is the normal operation. The switches
sometimes get corroded and need to be cleaned. Remove and spray with contact cleaner while working the switch. Many times, this will "fix" a problem
where a solenoid is not responding. When lowering, the pump runs to pressurize the air tank. If air tank is already pressurized, then the pump will
not come on.
--
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
 
I have the electrolevel 1, only one pump. Thanks guys for confirming pump running is normal even on down request. When i get the pressure side tight,
it should limit that as well.

--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
 
I could be wrong, It's been a minute since I messed with a stock system, but I seem to recall mine doing the same, until I took the switches apart and
cleaned them. They get corrosion on the contacts inside and start to get wonky.
--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
The pump running is a function of low pressure near the tank. If the key is on and the pressure is low the pump will run. If the key is off the pump
will not run. One exception to this is: If the key is on and the pressure is low, but the hold switch is on then the pump will not run. What controls
the running is a pressure switch mounted next to the pump, the hold switch, and the ignition switch. The up / down switches are NOT in the pump
circuit.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I just looked at the schematic and according to http://bdub.net/gmcmotorhome.info/figs/on.gif any one of the three switches can make power available to the
relay that sends power to the pressure switch:
1. travel/hold switch in TRAVEL
2. left raise/lower switch in RAISE or LOWER
3. right raise lower switch in RAISE or LOWER

In other words (in a working system with the ignition switch on and system air pressure is low) the pressure switch will turn the compressor ON if you
are in TRAVEL or if you are raising OR lowering either side.
--
1977 26 foot 403
 
Turn it anyplace from off and it will power the pump through the pressure switch - my E 1 does the same and a look at the wiring indicates this is
normal. The E 2 is completely different, only the airbags are the same.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
My later 78 (E2 with twin pumps) does not run the pump on lowering.

Pete
--
Cary, NC

1978 Center Kitchen Royale.
 
You must log in or register to reply here.
GMCMI Fall 2026 Rally
Applied GMC

Share this page

Share this page
Top Bottom
Back