ac quits blowing when going up a hill

[Flame]

1998 Chinook, V-10, 55,000 miles. Ac seems to blow cold...around 50 degrees when cruising with thermometer in the ac vent but...here lately when going up a incline as the engine rpm goes up to get up the hill the ac quits blowing all together!! When you reach the top of the hill or back off the throttle the ac starts blowing properly again. What gives? Low Freon? Vacume problem? It has not been that hot outside yet but we did have 100 heat index already with humidity and all this rain we are getting. Even setting still and at a idle and then reving the motor up a few minutes the ac still only blows right at 50 degrees.

[Rokrover]

I had a similar problem. Turned out to be the vacuum supply to the damper door for the air-distribution controls. More engine throttle gives less manifold vacuum and the default door position switches to defrost when it doesn’t get enough. So the first sign of leaking vacuum hoses, typical for aged Fords, comes at wider throttle.

The vacuum hose goes to a plastic reservoir bottle Ford built the engine bay panels around. The labor cost to replace with a Ford part in the same impossible location is horrendous. But wait - there’s a simple bypass! Just get a generic reservoir bottle, fit it more conveniently under the dash, then connect it with new hoses.

If this simple fix works you don’t need a new A/C compressor, drier, Schrader valves, Freon recharge, evaporator core and the whole works a shop might like to talk you into for $$$$.

[Blue~Go]

Edit: I see Rokrover posted while I was typing. Add him to the list of people who have done it. Rokrover: I need to do this fix - any tips? Specific canister to get (I don't know what to look for). Maybe you wrote it up here - I have not searched yet.

Welcome to the world of the Ford vacuum canister. It is a deep, secret world.....

Heh, okay, drama aside. So one thing the Ford vacuum system does is control the HVAC. But the engine uses vacuum too. If there is a lack of available vacuum, the HVAC's "safety mode" is to default to defrost (so you probably have AC but not coming out the vents is my guess). When you go up a hill, engine is thirsty for vacuum! If there is not enough to go around, HVAC loses. Take off some of that engine vacuum load and HVAC recovers it's functioning (you can hear the HVAC vacuum for example if you listen carefully after you turn vehicle off and while putting HVAC selector to OFF).

So my guess is a vacuum leak.

As it turns out the stock vacuum canister (reservoir) was purchased and placed in position, and then the van was built. It is now buried under your dash and above your right wheel well. It, it's check valve, or a nearby hose can fail.

Now of course it could be some other hose (if you pop open the "kidney" shaped thingie in the center of the top of the dashboard you can check some of the HVAC lines there), but the canister is very often the culprit.

For years the only choice was a million dollar repair (and probably some concurrent damage) as Ford removed the entire dashboard and heaven knows what else to get to it. Then our vehicles got a bit older and DIY'er and the Internet converged. The next stage was DIY folk removing the front passenger wheel, cutting a square hole in the inner wheel well sheet metal, and then extricating and replacing the canister.

Then someone figured out to just replace and bypass the canister with a new one mounted up under the dash (above passenger shins, inside). Now I think many (most?) Ford dealers even do it this way. There is an extensive thread on Ford Truck Forum and I think a few people have done it here too (Skillet?). In fact I need to brush up on this as I need to do mine now.

I'll come back and add a link to the FTF thread (long, but you can start and the end and work backwards). Also look for the threads here.

BG

FTF:
https://www.ford-trucks.com/forums/1077 ... m+canister

And here is one on the SMB forum. Starts with some diagnosing but then gets into the actual repair with a new canister.

http://www.sportsmobileforum.com/forums ... 11605.html

[chin_k]

I have not experience this on the rig yet, but I always wonder what is going on with my 84 Chevy when I forget to shut off the AC when climbing hill, and this explains it exactly.

[sm350bl]

I agree with what everybody has mentioned so far, vacuum related almost certain. sometimes its just a line. The vacuum reservoir is mounted under the a/c evaporator box. I have done several and its a fairly involved process. The evap box needs to come off the firewall to do the repair. Might still be worth to take it in somewhere and have somebody check it out. they may find a hose problem and be able to fix it. If they come back and say its the reservoir, then you can make your own decision from there.

[Flame]

After watching the video links ya'll sent me I ordered a new canister and check valve. I did the test it asked and mine failed. Proving I needed a check valve. But with the original valve and tank hidden I have chosen to just bypass all of that and mount a new check valve and aftermarket canister under the dash on the passenger side. Part will be here this morning and I will let ya'll know how it works out. Thanks so much for the troubleshooting info!!

[Flame]

Update... the route for the vacuum hose in the video is still very tough. Someone commented they went down their fender and into the cab with their hose. That looks a lot easier to me!! Basically, if you follow the antenna coax cable you will get there with little problem but...instead of going into the cab where the coax is,...right near it is a round rubber plug. Just poke a hole in it large enough to pass your vacuum hose through and you are in!! Now hook it to your canister and hang it somewhere out of the way and you are good to go!! I will attempt it later today. orileys forgot to send my hose with my canister so another delay of a few hours.

[Blue~Go]

I need to do this repair ASAP so this is timely. Thanks for reporting back as you go along.

On the alternative vacuum line routing: If I'm picturing what you are describing correctly, I can vouch for it. Reason is I installed a device a few years ago that isolates the hot water flow through the heater core in certain HVAC positions (to mitigate the "heated" vent and AC positions as designed). This required that I add a vacuum line between the under-hood area and the HVAC "tree" under the kidney shaped cover on top of the dashboard. (Interestingly there was a vacuum barb to use in the kidney panel area there like it was just waiting for me). I went around into the passenger fender cavity and then through a grommet in the side near the door hinge, which came out neatly in the passenger footwell/under-dash area. From there it was easy.

I didn't make this up though. I copied it from another Ford van owner who had installed the same device in the same way.

B

PS: More info, not to hijack but since I brought it up:

A fun side note is that this is made/sold for Ford trucks, and due to differences in the HVAC system design, it's actually easier to install in the vans than the trucks. When does THAT ever happen with a van?!

In case anyone is interested, it's the MAX AC valve. Works a little differently on our vans than the trucks as our HVAC is set up differently but does the same basic thing, which is keep hot heater core water from coming through while you have the vent or AC on. As it turns out Ford put something like this on some Rangers and maybe other vehicles. As stock, as I understand it, water is circulated through the heater core before coming to the fresh air vents or AC. My vents were warm enough that I was running AC when it was in the 60's outside (what a waste but windows open is noisy). My AC is colder now and the vents are less "heated" (they can still output some warm air after being parked with a hot engine since the air sits there in the tubes, basically).

https://www.dieselsite.com/maxacassista ... 0373l.aspx

[Flame]

Update... I just came back in from installing the canister with built in check valve. Ran it inside fender and thru rubber plug as stated before. Stuck canister and hoses up out of the way. Cranked her up and tested it and it works GREAT!! And I now get 18 mpg on gas!! Well, I might have made that part up!! Anyway...took all of 30 minutes and not even $20 in parts. Canister was $15 and I bought new hose and adapters. Saved me the dealer taking 12 hours and $1100 later!! They are going to have to make their money off someone else!! Go for it Blue. It's really easy the way I did it.

[Blue~Go]

Cool!

Would you be willing to elaborate a bit more?

1) Model or part number or link to canister (sorry if I missed it somewhere).

2) Details or tips on how you found or which hoses to attach.

3) Where/how you mounted the canister.

4) Anything else you feel like mentioning.

Maybe it's all in the video but I can't watch videos now (horrible signal).

I need to do this but am having a bit of trouble getting myself to start in on it.

Thanks,
BG