A/C Noise In Big Blue

[85lebaront2]

Bill - Remember that I have a 1990 system, not the later system that you have. The original hoses, aka manifold set, that I got from Huck had that "muffler" in the same spot as the new hoses/manifold that I had to buy to replace the leaky one. And it has it in the same spot, right up against the M/C.

As I said, the 1995 FSM doesn't show anything in the hose line at that spot, nor does the 1985. So it must be something with the 1990 system that I have.

I'll take some more pics, although it may not be until Monday as I'm not sure what the plans are for Father's Day. But there has to be a way to change things just enough to have clearance there. http://www.garysgaragemahal.com/uploads/6/5/8/7/65879365/thinking-26_orig.jpg

That may be it then, here is the only underhood picture of "Big Ugly" the 1990 F250 parts donor.

[Gary Lewis]

That may be it then, here is the only underhood picture of "Big Ugly" the 1990 F250 parts donor.

I think I see something in your pic, but that is on the line going to/from the compressor. I think the one on Big Blue is on the line to/from the condenser. Will try to get better pics soonest.

[Gary Lewis]

I think I see something in your pic, but that is on the line going to/from the compressor. I think the one on Big Blue is on the line to/from the condenser. Will try to get better pics soonest.

Ok, more pics. On the right is the line coming from the compressor, going into the side of the muffler, and then going towards the front. Note that it is sandwiched between the MAF sensor and the air inlet to the air cleaner box so it can't go up nor down.

On the left is the line coming from the muffler to the front and into the condenser. I'm guessing that the line coming out of the condenser is longer than the one that was originally in there, which pushed the muffler rearward and into the master cylinder.

However, having had 4 layers of inner tube rubber between the muffler and the M/C for two days the muffler no longer is up against the M/C. I think the rubber line has shifted a bit. But since I promised the shop that did the work I'd show them what the problem is, I'm going to leave the rubber out until tomorrow and take it in then. I think by then it'll be touching again and they can both see and hear the problem. Then I'll put the rubber back in and the problem will go away. And when I get it home I can figure out how to make the separation permanent.

[Ray Cecil]

Ok, more pics. On the right is the line coming from the compressor, going into the side of the muffler, and then going towards the front. Note that it is sandwiched between the MAF sensor and the air inlet to the air cleaner box so it can't go up nor down.

On the left is the line coming from the muffler to the front and into the condenser. I'm guessing that the line coming out of the condenser is longer than the one that was originally in there, which pushed the muffler rearward and into the master cylinder.

However, having had 4 layers of inner tube rubber between the muffler and the M/C for two days the muffler no longer is up against the M/C. I think the rubber line has shifted a bit. But since I promised the shop that did the work I'd show them what the problem is, I'm going to leave the rubber out until tomorrow and take it in then. I think by then it'll be touching again and they can both see and hear the problem. Then I'll put the rubber back in and the problem will go away. And when I get it home I can figure out how to make the separation permanent.

Glad you found it. I was reading through the thread, because I knew the answer. I figured you'd get it. I had this exact same noise on a chevy van I rebuilt. Turned out to be an ac compressor bracket was just barely touching another bracket I had installed backwards and was transmitting this exact same noise into the van. Glad you found your issue.

Ac compressors have to be coupled to the mass of the engine as well as possible or some odd resonances can occur.

Speaking of...my transmission crossmember in the 88 has a large dead weight hanging off the center where the trans mount bolts on. I assume it's to dampen some of the 7.3 idi vibrations.

[Gary Lewis]

Glad you found it. I was reading through the thread, because I knew the answer. I figured you'd get it. I had this exact same noise on a chevy van I rebuilt. Turned out to be an ac compressor bracket was just barely touching another bracket I had installed backwards and was transmitting this exact same noise into the van. Glad you found your issue.

Ac compressors have to be coupled to the mass of the engine as well as possible or some odd resonances can occur.

Speaking of...my transmission crossmember in the 88 has a large dead weight hanging off the center where the trans mount bolts on. I assume it's to dampen some of the 7.3 idi vibrations.

Isn't it amazing how much noise a little bit of "touching" can transmit? Man, this thing was OBNOXIOUS! Sounded like you were inside the A/C compressor.

As for the crossmember, yes some of them did have weights on them and I'm sure it was to dampen vibes. Bad, bad, bad vibrations!

[Ray Cecil]

Isn't it amazing how much noise a little bit of "touching" can transmit? Man, this thing was OBNOXIOUS! Sounded like you were inside the A/C compressor.

As for the crossmember, yes some of them did have weights on them and I'm sure it was to dampen vibes. Bad, bad, bad vibrations!

Yeah, it's crazy. I currently have an ac hose that sits in a bracket that holds the hose up and off of the air cleaner. If that hose doesn't sit in that bracket just perfectly the vibrations from my motor when warming up reverberate into the dash.

[Gary Lewis]

Yeah, it's crazy. I currently have an ac hose that sits in a bracket that holds the hose up and off of the air cleaner. If that hose doesn't sit in that bracket just perfectly the vibrations from my motor when warming up reverberate into the dash.

Thought I'd update this, maybe for the last time? http://www.garysgaragemahal.com/uploads/6/5/8/7/65879365/crossed-fingers-20-pixel_orig.png

I've played around with various routes for the hoses and tubing, and have come to realize that the muffler needs to nest between the MAF sensor and the master cylinder because the hose has to go between the MAF sensor's frame and the inlet air tube. But that it'll move a bit as the engine rocks on its mounts.

That movement tends to move, and ultimately toss out, the inner tube rubber I was using for isolation. So I've come up with the "solution" shown below. That's 1/2" heavy foam weatherstripping glued to the master cylinder so it won't go away. And in the shot on the right, which was taken from the engine's point of view, you can see a piece of foam insulation that protects the tube and hose from the MAF's plastic frame. Also, you can see a piece of inner tube that is glued in place between the MAF's frame and the end of the muffler.

So the muffler can move w/o losing the isolation pieces, but I think most of the movement will be taken up by the bends in the hose you can see running to the compressor in the left pic. We shall see...

[85lebaront2]

I think I see something in your pic, but that is on the line going to/from the compressor. I think the one on Big Blue is on the line to/from the condenser. Will try to get better pics soonest.

That was actually "Big Ugly" the 1990 F250 parts donor. What you see is the upper hose to the compressor (suction) and possibly the discharge line. Notice no MAF.

Here is Darth's current system:

[Gary Lewis]

That was actually "Big Ugly" the 1990 F250 parts donor. What you see is the upper hose to the compressor (suction) and possibly the discharge line. Notice no MAF.

Here is Darth's current system:

Yes, our lines run differently. Mine makes a run to the side before turning back. Looks like yours turns back earlier.

But, I think I have it sorted now. Will drive it a bit and see.