Intermittent Cabin Blower Motor Operation

[deppstein]

I noticed on our trip back from Colorado that the AC/Heat Cabin Blower Motor was cutting out for periods of time, then coming back on again. When on, it will run in all speeds, and the AC works fine. I've Googled the problem and found a number of threads about it...seems pretty common for older model Fords like ours, so I thought it would be good to query the group to see if anyone else has experienced this problem and what the fix was. A loose wire harness connection is one culprit mentioned, along with a worn thermal resister...sometimes even the motor itself. My plan is to take it to a reputable Ford dealer next week to have it diagnosed and addressed...but Im hoping that one of you all might have some sage advice for me before I turn it over to strangers. Let me know.
Much appreciated.
David

[sm350bl]

Is the electric blower motor shutting off or does it not just blow through the dash vents but still running? What is common on econoline's that are 20+ years old is the motor will stay running but air stops coming out of the dash vent and get redirected to defrost. If the motor is truly stopping, I would ideally like to get the mutlimeter out when the problem is happening and see where your getting / not getting power at. I like to start at the blower motor itself. If I give it a tap and it starts up again then I know it needs to be replaced. Then work my way back, blower motors, speed resistors and the switches in the dash are the biggest culprits. I have rarely had a physical rub through or disconnected wire cause a problem,

[Blue~Go]

Rich is referring to a common fault in the vacuum system that the HVAC uses to select where the air will come out (floor, vents, defrost, etc.). Any failure defaults to "defrost" position. When this begins to fail the fan will default to defrost only under heavy engine load, and after you crest the mountain or whatever it will come back to how you had it set. Eventually it never comes back.

The issue is related to the HVAC vacuum reservoir (or it's associated check valve or hoses. Unfortunately, Ford sat down with this reservoir and said, "Hey, nice reservoir. Let's build a van to enclose it!"

The "fix" has evolved over time and now we have three basic options.

1) The original "official" fix.
Remove huge chunks of dashboard and associated systems to get to deeply buried reservoir. Replace reservoir. Rebuild dashboard. As you can imagine this is expensive (time-consuming), and who knows what else will get shifted in the invasive process.

2) People (not dealers) realized you could remove the passenger front wheel, then cut a square out of the inner wheelwell sheet metal and there was the reservoir. Remove, replace, patch metal.

3) People realized you could just bypass the original reservoir and use a new one, usually tucked up under passenger shin area under dash.

Mine has gone out and I plan to do #3. Some Ford dealers do this now as well. I'd wager most people now do #2 or #3.

If it's an electrical or fan motor issue, then..... never mind! Or I suppose it could be a vacuum problem not related to the reservoir.

[Jlfchinook]

I did the #3 plan, putting it under dash panel on passenger side. Worked great. Several you tubes on it explained process quite well.

[deppstein]

You all are THE BEST! I will go for a drive and pay closer attention to what is really going on, but the HVAC vacuum issue seems like the most likely issue to me at the moment. The symptoms—particularly diverting to defrost and then coming back on the downhill seem to match most closely what we have been observing. If that is case, I will talk to mechanic (believe me, you don’t want me doing this one!) about Fix#3. I have an appointment with the mechanic on June 15th and will keep you posted.
Thanks again.
David

[caconcourse]

I did #3 fix as well. Here was my post with references to parts used: viewtopic.php?p=14447#p14447

PS I replaced the hose again already, because new rats ate through my first replacement! Either the hose is at a very strategic rat passage location, or they like the flavor of plastic...

[chin_k]

I would save the old hose, and use it as rat bait instead of wasting perfectly good peanut butter!

[deppstein]

I'm about to order parts for the vacuum reservoir Fix #3, so that I can have the parts on-hand when I take the Rig to the mechanic (hoping to save time in the shop)...Do any of you have an opinion on ordering the OEM Motorcraft parts vacuum res and check valve vs. the after-market Dorman with the built in check valve? I know they are both made by Dorman, so mostly wondering about the fit of the after-market up under the dash, as well as the effectiveness of having the check valve built into the reservoir instead of it being separate. All opinions welcome. Thanks
David

[caconcourse]

I might have been more impressed with the Ford parts if they hadn't failed to begin with, so I don't think there is any premium value to those parts. Secondly, having the built-in check valve eliminates a part as well as extra tubing between them, so I see the old Dorman part with the built-in valve as a better option. It's probably that little piece of hose connecting the OEM parts that disintegrates.

It is just a small air tank with a flap on the outlet, so you can suck air out and it won't go back in, creating a vacuum source to control the air valves. Without the check valve, continuous vacuum is needed in the hose at all times to operate the valves, and when you drive up a hill, the engine loses vacuum, causing the valves to revert to their default position (defrost), until the vacuum comes back when the engine is not working so hard going downhill or cruising.

The Dorman part is a ball, however, so it is a little bulky, but I've never had it get in the way when stuffed against the passenger bulkhead.

This really is a pretty simple do-it-yourself job. You just need a fish wire to push up through the existing tube hole in the bulkhead to the top of the engine compartment, so you can feed the new tube back into the passenger compartment. I used a piece of baling wire, and then inserted the end of the wire into the tube at the top and pulled it back into the cab to connect to the tank. At the top, there is already a junction to connect to the vacuum hose (red tube) from the engine. I've done it twice already, so it's no big deal.

Your mechanic may have his own opinion on how to fix it.

[deppstein]

Thanks Clay. I’ll ask my mechanic if he has a preference.