94 GT 5.0 only blows on HIGH

Lawdawg86

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Sep 30, 2020
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Ok, so I figured out the 5.0 runs off vacuum for the heat and ac, at first I was only getting ac and heat through the defrost vents, now that I fixed that tiny plastic line and plugged it back into the rubber AC vacuum line coming from the tree I’m only getting HIGH as a option. I have no low, or medium. I noticed a few other vacuum lines blocked off, think it’s the one that went to purge. Rest of the tree is hooked up. The entire cluster in the car looks brand new, so I’m not sure what’s going on, and since my Chiltons is useless, I may as well throw it out the door. Anyone have a Diag of the vacuum lines for the tree? Also what do you guys think, blend door or what? If the switch panel looks brand new I don’t suspect the high to work if low and medium aren’t. I’m lost. Anyways I thought I’d let y’all think it out. Again, before I had heat and ac but only through Defrost, then I found the tree, the small plastic line from the cab was broke off so I cleaned out the rubber cuppler, and put the small plastic line in the AC vacuum line that it came from before off the tree.
 
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Lawdawg86

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Resistor pack. It’s either blown or unplugged
Where is that at? I know it’s gotta be near the blower motor, but never worked on a blower motor in a mustang before let alone a resister pack in one. I’ve worked on them in Semis before but those were easy to find
 

Lawdawg86

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What is these wires? They come off a loom in the passenger side. Also someone please send me a vacuum diagram so I can sort this out as well. I’ve got a few vacuum lines that need replaced and some that I need to figure out where they go. Still not sure of the location of the resister
 

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Lawdawg86

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What vacuum line runs under the manifold on the 94 5.0? It’s the one that runs to that little canister shaped piece with wires going to it? I can’t figure out where under the intake it came from because I’ve got no diagram to show me let alone what that part goes to
 

Lawdawg86

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What vacuum line runs under the manifold on the 94 5.0? It’s the one that runs to that little canister shaped piece with wires going to it? I can’t figure out where under the intake it came from because I’ve got no diagram to show me let alone what that part goes to
I figured which one it was, the evap line. I had broken it and then had to run it back to evap check valve
 

KRUISR

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It should be installed with the coils in the air box (to provide cooling to the resistor while running). My Ford Contour has a similar device installed up behind dash, behind glove box near center of dash. I would suspect yours will be in a similar location.
 
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revhead347

Apparently my ex-husband made that mistake.
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Blower Motor resistor. It's a cheap part. If you look right above the fan on the HVAC box under the dash, there will be 4 wires plugged into a random point in the box. You replace the part screwed into the box.

The harness you are holding up is the test harness for the ECU. That's where you plug in to pull fault codes and stuff. You have a carb car, so it does nothing.

You will find all kinds of vacuum and wiring diagrams with this link.


Kurt
 
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Lawdawg86

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Blower Motor resistor. It's a cheap part. If you look right above the fan on the HVAC box under the dash, there will be 4 wires plugged into a random point in the box. You replace the part screwed into the box.

The harness you are holding up is the test harness for the ECU. That's where you plug in to pull fault codes and stuff. You have a carb car, so it does nothing.

You will find all kinds of vacuum and wiring diagrams with this link.


Kurt
Yeah I figured out it was the ecu test harness, as soon as I posted it I remembered where I’d seen it at in the book. I’ve replaced a million of them stupid resistors, they always go out when you least expect it. Funny thing is I have a twin brother and his antifreeze was low today on his truck, not in the actual radiator but the overflow tank, and his ac stopped working today. His should be an easy fix, I think his is actually the blend door. I forgot to see if the compressor was kicking in or not at all like if it was low on R-134.
 
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Lawdawg86

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What I can’t figure out is the difference in the Murry brand, standard ignition, or dorman. All different prices but all seem to be the same build style, with different prices
 

Lawdawg86

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I got it figured out. One of the lugs on the 4 wire harness was melted. Got another harness from the pull a part and also robbed the new looking Resistor as well. Got a very nice, arm rest lid not cracked, license plate bulb covers, two like new door pillar plastic pieces all for $4. Got the plug and resistor plugged in and we’re working on all settings. Now to get an alignment on this thing.
 
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KRUISR

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Got another harness from the pull a part and also robbed the new looking Resistor as well. Got a very nice, arm rest lid not cracked, license plate bulb covers, two like new door pillar plastic pieces all for $4.
Picking these parts at a pull a part is my default in similar situation. Great price too.
 
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revhead347

Apparently my ex-husband made that mistake.
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Jun 14, 2004
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I got it figured out. One of the lugs on the 4 wire harness was melted. Got another harness from the pull a part and also robbed the new looking Resistor as well. Got a very nice, arm rest lid not cracked, license plate bulb covers, two like new door pillar plastic pieces all for $4. Got the plug and resistor plugged in and we’re working on all settings. Now to get an alignment on this thing.

Very nice work. I don't think I have been to a pull a part in 15 years. I'm going to go out on a limb and say the Standard Motor Products was the higher price. It would have been my choice for quality.

Kurt
 
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