F-53 and dash A/C question

[dabrooks]

I wasn't sure if this is the right place to ask this question. I try to follow everything that is written about the Ford chassis that is posted on this forum and I have learned a lot from everyone. I did the "fix" and am really happy with the results.
While driving from Maryland to Memphis I had the dash a/c cut off several time when pulling a grade. I drove to Flordia and back in Feb and it never cut off. Is there some type of system built in to take the load off the engine?
Almost every time this happened I was pulling a grade at around 3000 rpms and I was steady letting of the accelerator trying to keep the transmission from down shifting. The a/c blower fan would cut completely off until I pretty much crested the hill and it would come right back on.
I have a 2001 35ft Georgie boy on a 2001 F-53 chassis. The heat and a/c controls are Evans. Any thoughts on why this happens?

[Tom N]

Possibly vacuum related, as the AC controls are operated by vacuum.

-Tom

[lx22]

Did it quit blowing out of dash and start blowing out the defroster? If so then you have a vacuum leak. Usually occurs under the hood where the plastic lines go to the recirc vac diagram or to the vac tank. You will have a black line going to vac source and usually a gray or white plastic hose to rec diagram. Usually the black line has a tee in it going inside cab and other to source and one going to tank.

[ga traveler]

Your AC has a default to defroster system. If you lose vacuum, the vacuum motor is spring loaded to defrost. If you have a slight vacuum leak, the AC goes to the defrost vents at the windshield. The next time it happens feel the windshield outlets and see if the air is not coming out there. If that is the problem, check all vacuum connections for leaks.

[ga traveler]

I see LX22 answered while I was writing my reply. Sorry for the same answer.

[Stan.Birch]

That's a rather common Ford "problem".

I suppose the thinking behind this "feature" is that if you have been pulling uphill for an extended period of time, then shutting down the A/C compressor would provide a useful assist. If it really bugs you, then adding a second vacuum reservior might offer assistance.

[jamesrxx951]

If you are at a higher throttle position the PCM will shut down the A/C compressor to allow for the most available power. If the engine is also running to hot, the PCM will shut down the compressor to help with engine cooling. The fan however should not be affected at all as it is part of the coach and not the chassis. If you did notice that the air started coming out of the defroster, then there is a slight vacuum leak in that system.

[grtharris]

Most of the heat and a/c system is supplied by the motorhome builder.
The condensor, Compressor and mounting hardware, Receiver/Dryer and High Pressure line from compressor to condenser are supplied my Ford with the chassis.
Sounds like a bad check valve in the vacuum system allowing the vacuum pressure to drop as the intake pressure drops. I think the check valve and vacuum reservoir are supplied by Ford.

[dabrooks]

Thanks for all the replies. I am in Tunica and have not had a chance to check anything out. I will be leaving tomorrow to head home. I will check to see if the fan blower switched to the defroster. I will report back as to what I find.

[Brockx]

The OP said he was feathering the throttle to keep from downshifting, seems that would keep the vacumn "up". Sounds more like a planned cut out system determined by temp or auxillary fans etc etc.. Some newer cars are that way due to small engines.
Just guessing all my stuff is too old to have it

[cb1000rider]

Originally Posted by dabrooks

The a/c blower fan would cut completely off until I pretty much crested the hill and it would come right back on.

I know of lots of vehicles that shut off the AC compressor when at WOT (Wide Open Throttle), but I've never seen one that cuts off the interior fan.

My 1999 F53 did not cut the compressor. My 2005 E450 does not cut off the compressor.

I suspect that your AC cut out isn't necessarily throttle related... I'd be interested to know if the fan turns off when on vent and climbing a hill.

[dabrooks]

I will be leaving tomorrow so I will see what happens. I believe the first time that the blower fan cut off I switched the control from max a/c to a/c and to vent and the blower did not come back on until I finished pulling the hill. I do know for a fact that I was able to pull the hill in overdrive at appox 2500rpms. I was down to about 50mph when the a/c fan went off and as soon as I crested the hill and started to pick up a little speed the fan came back on.

[teddyu]

dabrooks,

Re-read your original post. That post stated the blower motor cut-out. The WOT cut-out should not effect the blower. Chances are a vacuum leak is the answer to this problem. JM2¢...

[Brockx]

Originally Posted by teddyu

dabrooks,

Re-read your original post. That post stated the blower motor cut-out. The WOT cut-out should not effect the blower. Chances are a vacuum leak is the answer to this problem. JM2¢...

If it is a vacumn problem it should default to defrost, OP will know next time it happens to check defrost vent. He is not at WOT when it happens.