Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) MegaDork
1/23/21 12:39 p.m.

On my 2006 E250(ex-GRM van) I started noticing last spring that when towing/under load, and especially when going uphill, the a/c airflow would shut off. At first I thought it might be by design, being a 4.6, to conserve power. However, I discovered last fall that it also occurs when the heat is on. 
 

Doing some research, there's a vacuum operated flapper valve under the dash, and often either a leak will occur or the 1-way check valve will fail causing this problem. Ok, I can fix that. 
 

However, here's my question: I realize many vehicles have a "vent" setting on the dash to allow airflow - this van doesn't. Whenever you start it, even with the HVAC off, it pulls this vent door open. So is there any reason for its existence, or is it just a throwback from older vehicle technology that would have cost more to reengineer than just leave it in place?

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/23/21 12:54 p.m.

You do have a "vent" setting.  It's probably just called "panel."  Basically, any setting other than Max A/C or recirculation mode means that fresh air door is open.

On older GMs you had vent which was outside air from the dash.  All the other positions to the right used outside air.  Max A/C was the only one that used recirculation.

Similar thing for your Ford.  Panel is their word for vent.  The only recirculation setting is Max.

Not sure what year they switched over, but most new GM and Fords have the recirc button which gives you some control over that flap.

My old Branger has cable-operated doors, but my A/C will shut off when I floor it, too.  In my case, the problem is that it's slightly overcharged wtih R134 and keeps tripping the high pressure switch when the RPMs rise.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/23/21 1:05 p.m.

If you have this type, here is a breakdown of how the fresh air door operates.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/23/21 1:09 p.m.

The van version is a little differently labeled, but same thing.  Everything including "Norm AC" is outside air.  The only recirc is Max AC

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) MegaDork
1/23/21 2:20 p.m.

In reply to Curtis73 (Forum Supporter) :

Ah, thanks Curtis!

Although that's a little puzzling, because even on the Max a/c setting I still lose airflow under load/uphill?

Steve_Jones
Steve_Jones HalfDork
1/23/21 2:48 p.m.

You're losing it, or it's switching to the defrost vents? If it's going to the defrost vents it's a vacuum leak, and very common. They're set to fail in defrost mode for safety reasons. 

mjrj (Forum Supporter)
mjrj (Forum Supporter) Reader
1/23/21 4:29 p.m.

Vacuum leak, or the one way check valve has failed.  Ita a failsafe so if you lose vaccum you'll have defrost only.  We had some 2009 E350s at the old ambulance co. that this happened to, and it hapoens even with the new 2019 E350s we have.  The vacuum reservoir and check valve are under the hvac box on the engine compartment side of the box so access sucks.  The 2009s I put a GM-style vacuum reservoir under the dash.  The 2019s I removed a vacuum fitting underhood and put a check valve there.  I don't have the part number for the valve offhand, its a napa part.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/23/21 4:38 p.m.
Pete Gossett (Forum Supporter) said:

In reply to Curtis73 (Forum Supporter) :

Ah, thanks Curtis!

Although that's a little puzzling, because even on the Max a/c setting I still lose airflow under load/uphill?

Set fire to it and buy a Sprinter?  They don't have any problems [/sarcasm]

Totally kidding.  I loved all the Ford vans I had.  I agree with the vacuum leak/valve diagnosis.  At WOT when vacuum is low, the check valve is supposed to hold enough vacuum in the stuff under the dash to keep the doors/diverters where they're supposed to be.  My guess is that you either have a pinhole in a hose or the check valve is toast.  You can buy a 10-pack of those valves on Amazon for $8.

Purple Frog (Forum Supporter)
Purple Frog (Forum Supporter) HalfDork
1/23/21 5:29 p.m.

My  vacuum reservoir started leaking and I had to repair a few years ago.

Another sign of vacuum loss... your cruise control won't stay engaged.

I wish my 91 Honda Civic Si's dealer installed A/C compressor would have disengaged the clutch at wide open throttle.  Stupid me kept buying compressors.  I drove like I stole it, forgetting to turn off the A/C at high revs.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/23/21 8:41 p.m.

I'm pretty sure the cruise on those is electronic/servo.  It was on my any of my Ford's 98-up

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) MegaDork
1/23/21 10:42 p.m.
Steve_Jones said:

You're losing it, or it's switching to the defrost vents? If it's going to the defrost vents it's a vacuum leak, and very common. They're set to fail in defrost mode for safety reasons. 

Does that mean when the door is shut the airflow is diverted to defrost? I wired the door permanently open this afternoon. Though it's pretty rare to need defrost here. 
 

I can't reach my hand all the way to the defrost vents while driving, but when it's happened I couldn't tell there was anything blowing out of them. 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/24/21 7:44 a.m.

In reply to Pete Gossett (Forum Supporter) :

Vacuum controlled systems almost always default to defrost if there is no vacuum applied to anything, because the priority has to be to ensure the driver can see where they are going.

 

So, a control head leak, vacuum leak, or check valve failure, will result in the HVAC drifting to defrost under heavy engine load.

John Welsh
John Welsh Mod Squad
1/24/21 8:01 a.m.

Pete, your wrote: 

when going uphill, the a/c airflow would shut off. 

Could this be that you are loosing blower speeds or the blower itself shuts off?  No blower, no (or less) airflow? Are all 4 settings on your blower knob working?  

Blower Motor Control Module / Resistor.  $10-$20 part.

I had to do this on my F250.  Van should be similar: 

 

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) MegaDork
1/24/21 9:12 a.m.

In reply to John Welsh :

I don't think so. The airflow just stops completely until the load lessens enough, then it returns to normal. The real problem is being a 4.6, with the Miata on the trailer & the slightest headwind, I'll only have airflow when going downhill. 

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
1/24/21 10:50 a.m.
Pete Gossett (Forum Supporter) said:
Steve_Jones said:

You're losing it, or it's switching to the defrost vents? If it's going to the defrost vents it's a vacuum leak, and very common. They're set to fail in defrost mode for safety reasons. 

Does that mean when the door is shut the airflow is diverted to defrost? I wired the door permanently open this afternoon. Though it's pretty rare to need defrost here. 
 

I can't reach my hand all the way to the defrost vents while driving, but when it's happened I couldn't tell there was anything blowing out of them. 

No... different doors.

The default position for the vent/recirc door is closed (recirc).  The default position for the diverter is defrost.  It doesn't matter if the vent door is open/closed, you'll still have airflow.  The only difference is where the fan gets its air; outside or inside.

Forget about the doors for now.  Figure out why the air is stopping... or if it's just going somewhere else.  If the fan is running, the doors are completely irrelevant.   If the fan is running, there is air blowing out of a vent somewhere.  If the fan is stopping, I'm stumped.

The doors don't stop any air at all.  The vent door just chooses where the source of the air is - inside or outside.  The diverter just sends air to defrost, floor, or dash.  The bottom line is that either your fan is turning off, or the diverter door is just sending it somewhere else during low vacuum situations, and the change in sound and not feeling air from the dash is tricking you into thinking the airflow stopped.  But if the fan is running, airflow didn't stop, it just went out a different vent.

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