Ok, so I got the AC in my 79 charged up and she's blowing beautiful ice cold air. However, there's a new issue with the AC. The day after I picked it up from the shop I noticed a rumble when I had the AC on. Thought maybe my compressor went, but it's still blowing cold, and I mean COLD! So today I pop the hood, start her up and turn on the AC. It runs smooth for a minute or two then the rumble starts. I get out, walk around to the front, and notice the belt is flopping around like it's loose. So I shut it down, tighten the belt, since it was a bit loose, start her back up and the same thing happens. The belt is tight, but for some reason when the compressor kicks on it starts flapping wildly like it's about to come off. Anyone have any ideas why on Earth this is happening?? Everything is tight, the air is blowing cold, but that rumble is kinda unsettling.

 

Is there supposed to be any kind of idler pulley there when A/C is installed on the truck?
Is the compressor really hard to turn by hand with the belt off?

 

I don't think there's any kind of idler pulley. The compressor spins freely by hand. It's the weirdest thing I've ever seen.

 

Are you sure? Everything i've seen says if that truck had A/C it should have had either a single idler pulley or an idler pulley/arm assembly. That may only apply to V8 engines though, dont know.

 

I'll have to look. Hopefully that is the problem and it will fix it.

 

Well the only thing im wondering is if the idler only applied to V8 engines. Just noticed you have the 300 I6.
Maybe someone else will chime in here that knows more about whether or not it should have one.

 

I found an idler for the dealer installed AC for the 300, but I have factory. NAPA lists one but it's supposedly only for the V8's.

 

First of all, most every Ford with the piston style AC compressor does this at idle. It smooths out at speed. My '77 has made a rumble and the belt flop deal from day one 25 years ago. My step father had a '78 SB 2 wd F-150 and it did it too, he even traded it off because he thought something was wrond with it. My childhood best buddy had a '68 Shelby GT500KR he bought in 1971 for $2500 from a retired RR guy, 428 / full power / AC, etc .... and it did it too. It still does it actually .... when used (his mother has the car still, his BIL used top show it, my Buddy was killed in a wreck in '79).

It has ONE drive belt usually. Not a simple idler, there is adjustment priovided by adjusting what many would call an idler that bolts to the larg AC Comp bracket. You can tighten the belt and even tighten it too much leading to stretch, it'll still likely do it at idle.

Chrysler products of the day used a V-twin cylinder pump that was smoother at idle. Many Chrysler cars / trucks even had two matched belts pulling it .... always needed to replace in pairs as they had to be same length, etc going around same pulleys at same speed and same tension .... but they lasted.

You can replace that York or Tecumseh piston style compressor with a smoother model axial one though. http://cgi.ebay.com/ebaymotors/71-72...-/180292776340 just for example.

 

My York used to do that too, because apparently that's what they do. I got to the point when I came to a red light I would just flick it to vent to cut the compressor off then flick it back to A/C when I took off.

Now I have a Serpentine belt set up on my truck and run an FS10 compressor.

 

Dad's truck suffered from the famous belt flop and obnoxious rumble. He added a second idler between the compressor and crank, since the bracket was already made to accept it. Made a huge difference. It only holds the belt out about 1/4", but it keeps the belt flopping around from occuring.
My 80 F150 has dealer added A/C with the york compressor, but it sits right above the alt, and uses dual belts to go around the crank, alt A/C and WP.

That kit looks interesting. The pic doesn't actually enlarge when I click on the "enlarge" option, but it appears the older style fitting can thread right onto the comp. Handy for dad's truck, not so much for my 80. On dad's truck, the comp could be swapped without discharging the system, since it has those shutoff valve fittings at the comp. Best idea Ford, or anyone, ever had in regards to an A/C system, in my mind.

 

ARGGGHH!! Well, the AC belt flop is on hold. On my way to fishing the truck died. Throttle linkage broke at the carb. Had my friend tow me to the house and now I'm waiting for the new carburetor to come in tomorrow. I needed a new carb or rebuild anyways, but MAN I wanted to catch me some catfish!!

 

My '79 F250 that I owned in '84-'86 did the same thing, rumbled like hell but blew ice cubes. Also it seemed like I could literally see the gas guage needle moving whenever the A/C was turned on.

 

There were three different types of A/C available for 1973/79 F100/350's.

1) Factory installed integral A/C: The A/C is combined with the heater. The A/C controls are located in the same panel as the heater controls.
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2) Deluxe dealer installed A/C is combined with the heater. The A/C controls are separate from the heater controls.

The HUGE dash bezel sweeps across the entire right side of the dash, covers up the existing glove box. A separate glove box bolts to the bottom of the dash.
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3) Economy dealer installed A/C is separate from the heater as are the A/C controls. Has the two A/C switches mounted into a panel that also contains two registers.

This panel mounts into the dash, to the left of the extant glove box.
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* With factory installed Integral A/C: 1973/79 F100/350's with 240/300 I-6's do not use an idler pulley. Only the V8's have one (or two).

D8OZ-8678-A (replaced D0AZ-8678-A) .. Right (Passenger) Side Adjustable Idler Pulley-Use w/factory installed Integral A/C (Motorcraft YS103).

Applications: 1973/79 F100 302 / 1973/76 F100/350 360/390 / 1975/79 F150 302 / 1977/79 F100/350 351M/400 / 1973/79 F100/350 460 / Myriad 1970/79 V8 Passenger Cars.
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D0AZ-8678-B .. Left (Drivers) Side Fixed Idler Pulley-Use w/factory installed Integral A/C (no Motorcraft number).

Applications: 1973/79 F100/350 460 / Myriad 1970/79 V8 Passenger Cars.
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C5AZ-8678-C .. Left (Drivers) Side Fixed Idler Pulley-Use w/factory installed Integral A/C (no Motorcraft number).

Applications: 1973/76 F100/350 360/390 / Misc 1965/66 352/390/410/428 Passenger Cars.