Vacuum pump, what is it?

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Vacuum pump, what is it?

April 03, 2020, 01:08:27 pm

I've been trying to figure out how to get our dash heat to work and while I was behind the dash I noticed that our vacuum pump relay trigger fuse was blown. I put a new 15a fuse in but as soon as the ignition was turned over the fuse popped again. This happened twice so there must be a short somewhere but I don't know what the vacuum pump is or where it's located in order to check it.

Does anyone know where the vacuum pump would be located on our GV and/or what it's primary function is?

Thank you

Re: Vacuum pump, what is it?

Reply #1 – April 03, 2020, 01:20:52 pm

If it is the same pump as the 1993 U240, look through the front left grill or from underneath in that location. If tall enough you can open the driver's side nose "hatch" and look straight down.

Re: Vacuum pump, what is it?

Reply #2 – April 03, 2020, 01:23:11 pm

Quote

Does anyone know where the vacuum pump would be located on our GV and/or what it's primary function is?

I think if you open the driver side front cap access door and look straight down, you'll see it. Or crawl under and look up. Here is the one we had on a 93 225. Your pump might look a little different but I bet it's in the same place.

The vacuum controls the heater/AC duct flaps.
jor

Re: Vacuum pump, what is it?

Reply #3 – April 03, 2020, 01:38:35 pm

Quote from: jor – April 03, 2020, 01:23:11 pm

The vacuum controls the heater/AC duct flaps.
jor

Our duct flaps are stuck in the defroster position so I'm thinking the fuse and the flaps have something to do with each other.

The defroster position would probably be ok if we could just get some warm air out of the vents.

Re: Vacuum pump, what is it?

Reply #4 – April 03, 2020, 01:50:59 pm

Defrost is the default position in the absence of vacuum.

Re: Vacuum pump, what is it?

Reply #5 – April 03, 2020, 02:20:20 pm

The vacuum pump drives the actuators for the blend doors for the dash heat/ac system. As Brett said, the default position is defrost. You could try 12V directly to the pump and see if it will run. That would help track down the short causing the fuse to blow.

If you are not getting heat out the defrost or some other duct, the vacuum pump is not the problem. Does your fan blow? You will need to start checking the heat supply and smarter folks than me will have some suggestions.

The third photo above shows the vacuum reservoir (the round black ball.

Rich

Re: Vacuum pump, what is it?

Reply #6 – April 03, 2020, 03:34:44 pm

Quote from: Rich Bowman – April 03, 2020, 02:20:20 pm

The third photo above shows the vacuum reservoir (the round black ball).

Tyler,

There is also a vacuum switch on the firewall that tells the vacuum pump when to turn on and off. If the pump runs when powered directly by a jumper wire, but will not otherwise run, it could be a faulty vacuum switch. The switch (on our coach) is located on the firewall near the "round black ball" reservoir mentioned by Rich.

See the thread linked below for a photo (and discussion) of the switch:

Vacuum switch for dash AC controls.

Re: Vacuum pump, what is it?

Reply #7 – April 03, 2020, 04:00:14 pm

So, this is probably the problem. Your sliding control has gone south or at least partially south. The slider on the Ford controls starts leaking when it's in the left most position. This causes the vacuum pump to run all the time and burns it out. Put a plastic stop on the slider so it can't go all the way to the left but stops a half inch or so from the end. Any kind of 12V vacuum pump will do. Check Ebay as there are lots of them for sale. Ours as well as several others have had the problem.

Pierce

Re: Vacuum pump, what is it?

Reply #8 – April 07, 2020, 01:41:40 pm

The vacuum itself has a short in it. I ran 12v directly to the pump and it was blowing the fuse as soon as I touched the wires together. I found the vacuum line that runs to the dash was broken in two places which may have caused the pump to run until it burnt itself up.

Can I get a generic vacuum pump and small vacuum hoses at an auto parts store?

I don't know if we're even getting hot water to the front or not but i can maybe fix one problem right now haha.

Re: Vacuum pump, what is it?

Reply #9 – April 07, 2020, 01:50:02 pm

Yes, you can get another style/brand pump.

The OE pump is better quality and more expensive than most replacement, but any vacuum pump designed for diesel vehicles will work.

You may have to rewire it as some have built in pressure switches vs the remote switch you now have.

Re: Vacuum pump, what is it?

Reply #10 – April 07, 2020, 01:50:59 pm

Buy the pump online not many auto stores would have it, maybe O'reilly's.

Re: Vacuum pump, what is it?

Reply #11 – April 07, 2020, 02:02:46 pm

Our pump is a Gast model: MOA-V111-JH and at between $300 and $400 to replace it may very well stay broken.

We have to be selective about the projects we spend that kind of money on and I'm not sure this one makes the cut haha.

Re: Vacuum pump, what is it?

Reply #12 – April 07, 2020, 02:11:04 pm

Tyler, try one of these.
Amazon.com: Dorman 904-214 Electrical Vacuum Pump for Select Ford/Dodge...

You can find these for a bit less. Much less and they are copies. The copies may be fine for what you need and on a budget probably OK

Electric Engine Vacuum Pump For Ford F-250 Diesel HVAC 4WD 6C3Z2A451A...

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Re: Vacuum pump, what is it?

Reply #13 – April 07, 2020, 02:25:27 pm

Quote from: Roger & Susan in Home2 – April 07, 2020, 02:11:04 pm

Tyler, try one of these.
Amazon.com: Dorman 904-214 Electrical Vacuum Pump for Select Ford/Dodge...

You can find these for a bit less. Much less and they are copies. The copies may be fine for what you need and on a budget probably OK

Electric Engine Vacuum Pump For Ford F-250 Diesel HVAC 4WD 6C3Z2A451A...

Thanks Roger when we get to Montana i might order one of those and see if it'll work.

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Re: Vacuum pump, what is it?

Reply #14 – April 07, 2020, 02:30:16 pm

What can I check to see why we're not getting any warm air out of the defroster vents?

I have turned the valve to the water heater off and haven't found another valve that would prevent water from entering the heater core.

Could the heater core be plugged or something?

Re: Vacuum pump, what is it?

Reply #15 – April 07, 2020, 05:27:49 pm

There is a heater valve located behind the passenger side lift-up cover on the nose of your coach. This valve controls water flow into the heater core. The valve is mechanically operated by a wire "push-pull" cable. The other end of the cable is attached to a lever that is part of the heater control panel. Lift up the dash cover and move the heat temperature control lever back and forth from HOT to COLD. You should see the cable moving in and out of the cable sheath.

If the cable is moving at the dash control, then have Hannah move it while you watch the water valve outside under the hood. See if the valve is moving from open to closed position. If it doesn't move, then the valve could be corroded inside and plugged up.

Re: Vacuum pump, what is it?

Reply #16 – April 07, 2020, 07:36:10 pm

Quote from: Chuck & Jeannie – April 07, 2020, 05:27:49 pm

There is a heater valve located behind the passenger side lift-up cover on the nose of your coach. This valve controls water flow into the heater core. The valve is mechanically operated by a wire "push-pull" cable. The other end of the cable is attached to a lever that is part of the heater control panel. Lift up the dash cover and move the heat temperature control lever back and forth from HOT to COLD. You should see the cable moving in and out of the cable sheath.

If the cable is moving at the dash control, then have Hannah move it while you watch the water valve outside under the hood. See if the valve is moving from open to closed position. If it doesn't move, then the valve could be corroded inside and plugged up.

I had tracked down the other end of the temp control cable because it was bound up at the dash. We made sure that the valve was in the correct position.

Re: Vacuum pump, what is it?

Reply #17 – April 10, 2020, 09:49:31 pm

Quote from: The Soft Boulders – April 07, 2020, 07:36:10 pm

I had tracked down the other end of the temp control cable because it was bound up at the dash. We made sure that the valve was in the correct position.

What part of Montana are you headed? In my coach, theres an auxiliary pump switch by the dock light and over ride switches. I have to turn that little pump on when shes cold. It pumps hot coolant to the front. I turn it on for a minute or two and the heater works fine. Without that little pump it will stay cold.

Re: Vacuum pump, what is it?

Reply #18 – April 10, 2020, 10:12:41 pm

MT Ted,

That aux coolant pump is fitted to the DD 6V92, but is not used on the OP's Cummins C8.3 (I don't know about CAT engines).

I have heard it said (jokingly) that the 6V92 doesn't make enough HP to push the coolant all the way to the front of the coach.

No offense intended.

Re: Vacuum pump, what is it?

Reply #19 – April 10, 2020, 11:14:14 pm

Lol Chuck, it not the HP, ist the water pump on Detroit's

Re: Vacuum pump, what is it?

Reply #20 – April 11, 2020, 12:56:42 am

Quote from: MT Ted – April 10, 2020, 09:49:31 pm

What part of Montana are you headed? In my coach, theres an auxiliary pump switch by the dock light and over ride switches. I have to turn that little pump on when shes cold. It pumps hot coolant to the front. I turn it on for a minute or two and the heater works fine. Without that little pump it will stay cold.

We're headed to Hungry Horse for the summer.

On the drawing we have, it shows one of relays in isolator board area to be for the aux pump but that it's only applicable to the U300 series.

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