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Old 07-03-2022, 09:32 PM   #1
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Cab A/C switching output when accelerating

I have a 2004 Jayco Greyhawk 31' with a Ford E450 cab. We took a trip this last week and I discovered something strange with the A/C in the cab. I put it on Vent, or Regular A/C and for the most part the air came out of the vents on the front of the dash, as expected. However, every time I would go up a hill and stepped on the gas to maintain speed, the engine would rev higher, or the tranny would shift into the next gear down... the A/C would switch to "Mix" and come out of the dash and floor. As soon as I would level off and let up on the gas, it would return to normal. I've never had that happen in any other vehicle!

A little background... when I first got this unit 5 months ago the air would only come out of the defrost against the window... no matter what the switch was pointing to. After some research, lots of people were talking about the vacuum switching wasn't working and there's an easy "bypass" of one of the vacuum lines. I redirected the line going out under the hood, added an extension and connected it to the right spot under the passenger's foot area. Voila! The air would come out wherever I directed it. I have no idea if that "quick fix" is related to this or not.

Any ideas are appreciated! Thanks in advance.
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Old 07-03-2022, 09:53 PM   #2
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Quote:
Originally Posted by papademuchos View Post
I have a 2004 Jayco Greyhawk 31' with a Ford E450 cab. We took a trip this last week and I discovered something strange with the A/C in the cab. I put it on Vent, or Regular A/C and for the most part the air came out of the vents on the front of the dash, as expected. However, every time I would go up a hill and stepped on the gas to maintain speed, the engine would rev higher, or the tranny would shift into the next gear down... the A/C would switch to "Mix" and come out of the dash and floor. As soon as I would level off and let up on the gas, it would return to normal. I've never had that happen in any other vehicle!

A little background... when I first got this unit 5 months ago the air would only come out of the defrost against the window... no matter what the switch was pointing to. After some research, lots of people were talking about the vacuum switching wasn't working and there's an easy "bypass" of one of the vacuum lines. I redirected the line going out under the hood, added an extension and connected it to the right spot under the passenger's foot area. Voila! The air would come out wherever I directed it. I have no idea if that "quick fix" is related to this or not.

Any ideas are appreciated! Thanks in advance.
What is happening is on the Ford vacuum controlled a/c controls is when you step on the accelerator you loose vacuum. It is a easy fix under the hood you should see what looks like a ball mounted somewhere under the hood with two vacuum lines on it. This is a vacuum reservoir. It will have two vacuum lines hooked to it take them off one at a time and see which one doesn't have vacuum on it with the engine running. Then get a vacuum tee to match vacuum line size from your local parts store and install it in this line along with the line you hooked to the air box and that will stop the vents from changing when you step on the gas. There has been this reservoir on every Ford with vacuum a/c heat controls since they started using them. It was Ford's way of using the kiss method.
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Old 07-03-2022, 10:58 PM   #3
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Thank you SeaBreazer - I found this youtube video that explains exactly what you're talking about with great explanation and a visual to help with troubleshooting. I'll be looking at this tomorrow on my rig.

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Old 07-03-2022, 11:20 PM   #4
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That is exactly what I was talking about if you find the original line you should be able to change the check valve and replace the line to the one you installed on the controller make sure to cap the port on the intake where you ran your original fix from.
Glad to help.
Let us know if you get it working right.
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Old 07-05-2022, 11:07 AM   #5
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The engine/ AC system is equipped w/ a CHECK VALVE and VACUUM RESERVOIR, that is inaccessible without a $1k repair, but there are workarounds. Your SYMPTOM implies bad CHECK VALVE, simple repair is just ADD a 2nd one at an accessible location under hood? Adjacent to OIL FILL CAP, top of firewall, more toward driver's side of cap, buried in black protective corrugated, find the RED PLASTIC VACUUM LINE (that goes to the INTAKE MANIFOLD) It has a BLACK RUBBER BOOT where it connects to BLACK PLASTIC, Pull this joint apart, leaving BOOT on the Red Plastic. Using a combination of 1" to 2"-4" lengths of 1/8"ID black rubber vacuum line and clear 1/4"ID tubing and/or 1/4"ID Black RUBBER TUBING, ADD a new VACUUM CHECK VALVE here at this joint between RED/ Black plastic. Install so that you can BLOW thru valve into the red tubing. If you cannot, flip it around. Exact valve you find will determine 1/8" or 1/4" tubing, and/or combinations for best connections? I will try to make/ upload pictures and show MINE later today. P.s. REASON for symptom is engine loses vacuum when you accelerate, and AC system maintains damper position because CHECK VALVE THEN CLOSES, AND DAMPER OPERATES from vacuum in RESERVOIR. HOPE THIS HELPS. p.s. 2-PORT VACCUUM CHECK can be found local parts store or ONLINE HELP section sometimes, or maybe NAPA. NOT near as common/ easy to find as used to be years back, before digital motors vs vacuum operators. GOOD LUCK.
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Old 07-05-2022, 02:36 PM   #6
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PDF file link will be posted after file approved
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Old 07-05-2022, 11:41 PM   #7
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<< if you find the original line you should be able to change the check valve and replace the line to the one you installed on the controller make sure to cap the port on the intake where you ran your original fix from.>> Since the original CHECK VALVE is made into the VACUUM CANISTER, and is a $1000 job to access/ replace by dealer/ factory procedure, you are BEST TO just ADD new in series in the line at accessible location UNDER HOOD. See my other posts in this thread?
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Old 07-05-2022, 11:43 PM   #8
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https://www.irv2.com/forums/download...do=file&id=411


PDF OF NEW VACUUM CHECK INSTALLED UNDER HOOD
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Old 07-06-2022, 10:10 AM   #9
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Thanks for the details and the picture! Super helpful. The RV is out now, but will be looking at it when it comes back.
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Old 07-08-2022, 06:30 AM   #10
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this just happened to me,
but worst is I think I ruined my compressor.

By the time I figured out what was wrong, I had let my compressor run at 60 mph for hours at a time and I think it ruined my compressors.

When I pulled into my last campground I could hear a bad ratteling noise, thou, the AC was putting out cold air because I was at idle.
Of course I.m 1000 miles from home, and 300 miles from my destination.

I wanted to disconnect the power to the compressor so it wouldn't come on. I It sounded to me it was cycling on/off no matter how I had the inside controls set, so, I wanted no power going to it. I could not determine the fuse, nor pull the plug off of the compressor, but I was able to remove the plug from the low pressure sensor and it appears the compressor now has no power.
Im very apprehensive about my 3 hour trip today as of course I don't want to breakdown on the side of the road.

The water pump appears to be good, no leaks, running at 185 degrees.
Of course it could be the idler wheel, on the tensioner wheel which I will replace as soon as I'm at my next stop of three weeks, but today I will be riding on edge.

It makes sense that I could have ruined the compressor as its not good for a AC system to run without blowing air over the evaporator. I.m just hoping the compressor bearings aren't bad and it seizes up and i loose the belt. This would be a nightmare as having the ac compressor changed while traveling will be very costly ( Last time it cost me $2000 and they didn't even fix the AC, that was just to make it drive able ).

If you experience this loss of AC at high speeds disconnect the power to your compressor ASAP until you fix it,, You can fix this problem for less that $50 but if you wait it could cost you thousands.

Kip
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Old 07-13-2022, 01:58 PM   #11
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Thanks for the info. I had a '02 Ford Windstar and that same exact thing happen to us. Step on the gas and a/c would change vents. Now in my '05 E450 I'll know how to chase down the problem should it occur.
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Old 07-13-2022, 10:38 PM   #12
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KWFTLAUD wrote: <<I could hear a bad ratteling noise>> a Few OTHER possibilities for rattle: 1) 85 Octane by mistake= valve clatter; 2) HEAT SHIELDS/ EXHAUST TAILPIPE MOUNTS. When a tailpipe hanger breaks and pipe bouncing around, it can transfer the noise all Over. I lost a 8-ftx 3" tailpipe behind rear axle, Heard it hit that pothole at the gas station drive, and then the big CLANG at THE X-WAY ON-RAMP. and I pulled over and looked, but did not see or HEAR or realize, until home from trip and under rig working on GEN :-) Not sure if hanger weld broke first, or pothole peeled it loose?
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Old 07-14-2022, 08:57 AM   #13
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Update:

Vacuum issue:

I got a 2 port vacuum check valve, Dorman #47149. I put that in the red vacuum line on the firewall just right of the blower motor. This did solve the vent changing problem. I took the line apart at the red line connection and I sucked on the black line. I then put my tongue on it and it held the vacuum. So, for $8 I thought it can't hurt to try a simple fix, and it worked !

THe rattle: I thought I had fried my compressor and it was causing the rattle. So I pulled off the connection to the low pressure switch on the AC system to make sure not power went to the compressor, hoping the compressor would run freely and get me to my destination. That seemed to work for the next 300 miles. Then, on the cold start a few days later I heard the rattle again. Its not consistent. I drove it 200 miles to my next stop. It now appears its not the AC. I have a 300 mile trip to get to a stop where I will be able to work on it. I am not going to connect to AC back up until I get there thou I believe it will be fine.

My next plan of action is to change the tensioner wheel and the idler wheel, hoping that is where the rattle is coming from.

THe engine has 83,000 miles on it, 2001 V-10.
Anyone have any suggestions on where to look for the rattle?
I'm almost positive its coming from a component that is driven by the fan belt. Its not losing water nor running hot to I don't think its the water pump.
Any suggestions what to look for?
Are the idler wheel and the tensioner the same pully?

Kip
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Old 07-14-2022, 11:04 PM   #14
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So first go back and shake your tailpipe? 2) Tensioner wheel diameter SMALLER THAN IDLER, and 3) (Passenger side Idler mandatory= keeps belt from rubbing on tensioner mount) 4) Driver side idler= optional, but (some) blame high speed clatter (similar to valve clatter?) on the missing driver idler= belt flap at certain speed/ harmonics, so they add. I also added recently for giggles/ grins. I suspect driver side can be small or large, as no belt rubbing issues. Good Luck.

I recently started my E450sd v-10 after 2-3 months, and had a loud bearing growl I would have sworn was my ALTERNATOR using a rod as stethoscope. So bad, I was scared to run much, afraid it would seize and blow belt. BUT new alternator, tensioner, idler did NOT cure, so next day pulled serpentine and checked water pump and PS/AC compressor again, and changed belt; Only slight improvement, but the longer it ran the better it sounded. MY resolution still pending :-( Was gonna run/ troubleshoot more today, but did not make it.
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