Resolved Needing some guidance on the A/C vacuum lines again

[mikeah]

Hey all,

Been working on various fixes lately and realizing I would likely to take another stab at fixing the air conditioning controls being stuck on defrost in my 1988 Mustang GT.

The heater core was replaced once upon a time and you can clearly tell that by the photos, but I'm curious where does the HVCB -> FCCB line (based on the diagram) between the firewall and the vacuum cluster go? I can't seem to find a good way to check if it's actually connected or damaged (even using an endoscopic camera it's difficult to tell). In my case, it is behind the glove box, and then it goes up through a small crack in some plastic near the heater core. I can't think of a good way to check this other than removing the whole dashboard (please tell me I don't have to haha).

I know the A/C reservoir canister is good as I went through the effort to swap that with a known good one, so to me I'm guessing there is an issue between the vacuum line in the firewall, and that cluster of lines that are joined together behind the glovebox.

Hoping this makes sense and that I can sort out why the controls are stuck on defrost even when selecting other options.

 

[limp]

You need to buy one of these manuals.. This is on Ebay right now.... BEST manual I have and I have ALL of the Ford Service manuals for my 83

1988 Ford Mustang Electrical Vacuum Troubleshooting Procedure Service Manual | eBay

Electrical & Vacuum. Physical Paper Manual. Loaded with diagrams & illustrations to help disassemble, repair & reassemble various components.

www.ebay.com

 

[mikeah]

You need to buy one of these manuals.. This is on Ebay right now.... BEST manual I have and I have ALL of the Ford Service manuals for my 83

1988 Ford Mustang Electrical Vacuum Troubleshooting Procedure Service Manual | eBay

Electrical & Vacuum. Physical Paper Manual. Loaded with diagrams & illustrations to help disassemble, repair & reassemble various components.

www.ebay.com

Thanks for this. I actually realize now this entire book is available from a thread on StangNet forums (https://stangnet.com/mustang-forums...ctrical-vacuum-troubleshooting-guide-evtm.63/).

Looking at that section in the PDF, it seems that the diagrams provided are the same as what I have for the vacuum distribution, but it doesn't cover the actual lines and diagnosing them (other than the electronics) from what I can tell.

I'm wondering if it makes sense to replace this whole line given the inability to actually see the quality of it between the firewall and that junction.

EDIT: I see the vacuum tester steps further up now and missed those earlier. Reading over them now.

 

[General karthief]

I would buy a inexpensive hand vacuum pump, start at the vac tree connector for the hvac and test if it holds vacuum, work your way back to the controls.

 

[mikeah]

Thanks all, I'll snag a hand vacuum pump tonight at Harbor Freight and see if I can get some sort of clarity. I printed out the troubleshooting section of the guide also.

 

[mikeah]

Update here!

We've got pressure in defrost mode which means my line from the engine bay through the firewall and into that distribution block under the glove compartment is good. Floor also seems to hold pressure, but any and all of the other modes never hold any vacuum pressure. So based on the diagrams, I am assuming I need to troubleshoot the red and blue hoses (most likely the red hose).

Going to have to likely dig in a bit deeper at the controls and beyond to see what stands out.

If anything seems immediately obvious based on this behavior, I'm all ears! Thanks again and I think I'm getting closer to finding this darn leak.

 

[mikeah]

Found the problem, but need some guidance on how to proceed.

The issue is shockingly the actual selector knob control mechanism for the climate control. I felt the air escaping underneath when testing earlier and noticed the bottom of the hose connection going into the vent selector knob is cracked.

I checked LMR, but can't find this part. Any ideas on how to replace this and/or find the selector mechanism?

The residue is definitely disgusting, but I'm guessing this was from when I smoke tested the vacuum lines once upon a time.

 

[AeroCoupe]

Is there a Ford part number on it?

 

[AeroCoupe]

Here is one on eBay for $50.

1987-1989 Mustang HVAC Heat AC Control Climate Panel Switches Heater *For Parts* | eBay

It’s missing the Fan speed selector switch and is being sold for parts only. The part shown are what you receive.

www.ebay.com

 

[mikeah]

Thanks for that! I looked at a few with the hose and electric cables trimmed short, but I am worried about the hoses. How much of a pain is connecting the old hose piece to this or splicing it in? I don't entirely understand how the hose connection is disconnected from this part.

For the part number, it's a Motorcraft E6DH-19D961-AC, but I can't seem to really find anything online relating to that part. It's possible I'm confusing some of the characters on it.

EDIT: I bought that one, took the old hose connection off my existing one, but in the process I broke the 2 plastic posts with the metal nut. I'm assuming I'll need to come up with a better way of taking the cut hose harness off of the eBay item.

 

[General karthief]

Those metal nuts should twist off pretty easy, maybe the plastic was brittle?

 

[mikeah]

That seems plausible, hoping the part I receive is in a bit less of a brittle condition. Worst case I suppose if those snap I could drill a small screw in or epoxy it onto the block.

I did dig into this part a bit more and I did find another model # which is YH-1447. I looked at a few on eBay, but all of them were used or clearly damaged (one claims to be working, but it has a crack in the housing that looks just like mine -- doubtful that it maintains vacuum).

Wondering why this part is just non-existent now for buying a brand new replacement. I'm fine with using a used one, but I do wonder how long it will last given the age of the plastic, etc.

 

[General karthief]

You don't find them new because it is not prone to failure, I am under the impression that the manufacturers (likely bean counters) provide replacement parts for maximum of 10 years, if they see a part that has a low failure rate, replacement parts will not be available in large numbers, it's not uncommon for a part to be used in several different models over several years but again low failure rate=low part reproduction.
I have found some replacement parts for 'the dump truck' (97 Super Duty) on 'obsolete ' parts companies.
Junk-ahh-I mean salvage yards used to have a 'interchange catalog' they used but I don't know if they are still relavent.

 

[mikeah]

You don't find them new because it is not prone to failure, I am under the impression that the manufacturers (likely bean counters) provide replacement parts for maximum of 10 years, if they see a part that has a low failure rate, replacement parts will not be available in large numbers, it's not uncommon for a part to be used in several different models over several years but again low failure rate=low part reproduction.
I have found some replacement parts for 'the dump truck' (97 Super Duty) on 'obsolete ' parts companies.
Junk-ahh-I mean salvage yards used to have a 'interchange catalog' they used but I don't know if they are still relavent.

Yeah, we used to go to a few junk/salvage yards in the Brandon area (Davidsons, etc) when I was in Tampa, but I haven't gone to them in years (over an hour drive for no guarantee of a part).

I definitely can see the failure rate being low given that this part isn't in production. I imagine if I'm still having issues after this, my next approach will be sealing the leaks in the housing, etc, instead of chasing down another part probably (FlexSeal or Epoxy will probably get the job done).

Hoping when I put this together I don't damage the temperature controls. That was kind of a pain to disconnect and I couldn't find much guidance on adjusting it, etc.

 

[General karthief]

Yeah, we used to go to a few junk/salvage yards in the Brandon area (Davidsons, etc) when I was in Tampa, but I haven't gone to them in years (over an hour drive for no guarantee of a part)

There used to be a yard in the area of Hwy301 and I4 but they closed like 20 years or so ago.

 

[Noobz347]

That seems plausible, hoping the part I receive is in a bit less of a brittle condition. Worst case I suppose if those snap I could drill a small screw in or epoxy it onto the block.

Drilling the plastic is risky. Try these with a small drop of superglue in the center of the pad:

Amazon product ASIN B0CKWPJYMS
View: https://www.amazon.com/Adhesive-Mounts-Holders-Squares-Screws/dp/B0CKWPJYMS/ref=sr_1_5?dib=eyJ2IjoiMSJ9.M8ljlshzw5FlPARKlnoPbR9baf64RylwPq-WgiN7IqgTmUhkWpiSYQIxF-PQuqCtlDc0CiDJvF4bHSZkcjRcpKSwTq8tkG64yQ_UFask63tjG20lFsHAouGP1I8zO6Zqkkq-i1_lg50NUXCMNZG2zq3ZTg6P1lDsierhJnmmLMs5fCSk3H0RXjjTdL9VgX9hvcUCycHhL8cGj9tiI1L022MeR-MRKF9hLj0oj9a32uU.-FjtySLjhWWmVEsPnmL_eTYkGslk2X8LtnVPKPOWbEU&dib_tag=se&keywords=zip%2Btie%2Bstick%2Bpads&sr=8-5&th=1

 

[limp]

Try to find a pre 86 heater/AC controller... Unobtainable...

 

[mikeah]

Anddd just like that I'm in a bad spot once more. Seller cancelled and refunded the item just now. I guess I'll poke around on eBay some more. There's one in Miami that's just this part and they said it works, but I can see the gap at the bottom just like mine has. Not sure if it's worth risking the biscuit.

Motorcraft YH1447 AC heat air blend damper door vacuum switch . | eBay

Motorcraft YH1447 AC heat air blend damper door vacuum switch . A working switch. Moves freely in all positions. no broken vacuum connections and mounting tab intact.

www.ebay.com

EDIT: Actually, I ended up buying https://www.ebay.com/itm/1661857671...pid=5335821607&customid=&toolid=10001&mkevt=1. Given the pictures and the lack of any obvious wear I think this is my safest bet.

 

[Willybill32]

Try to find a pre 86 heater/AC controller... Unobtainable...

I see pre-86 HVAC controllers frequently on Facebook.

 

[mikeah]

So the part just arrived, got it installed and unfortunately I'm not in any better of a situation. I will say the part looked excellent and there is no air leaking from the replaced part from what I can tell.

So testing the following lines with vacuum I got:
Max A/C - No pressure
Norm A/C - No pressure
Vent - No pressure
Floor - Held pressure
Mix - Held pressure
Defrost - Held pressure

I also checked the A/C canister with 10 PSI and it held.

I'm guessing this means I need to diagnose the yellow and white hose. Any tips on how to follow it and find the leaks as I diagnose?

I'm guessing most of these lines are hidden away behind the dash so not sure how best to approach this now.

Thanks again for the help!