Close



Results 1 to 14 of 14
  1. #1

    Cool 1986 Mustang HVAC control

    My '86 GT is up and running, and now we're working on the A/C system. The evaporator coil, accumulator and all lines have been replaced, leaving only the compressor and condenser coil from the original car. The system holds pressure, but we can't get the compressor to cycle automatically. Tracing thru all of the components, the dash-mounted control for the blower motor, temperature and function (heat, a/c, defrost, etc.) does not consistently make contact when in the A/C mode. Does anyone know if I have to replace the whole control unit, or is there a switch component that can be replaced?
    Last edited by wraithracing; 04-01-2020 at 07:09 AM. Reason: Text color

  2. #2
    FEP Senior Member liv2roc's Avatar
    Join Date
    Jul 2009
    Location
    Cherryville n.c.
    Posts
    774

    Default

    did the 86 have the kickdown cut off for the ac like the carb cars had that cut the ac off at full throttle. I had to bypass it on my 84 when I changed the carb.

  3. #3

    Default

    Quote Originally Posted by liv2roc View Post
    did the 86 have the kickdown cut off for the ac like the carb cars had that cut the ac off at full throttle. I had to bypass it on my 84 when I changed the carb.
    liv2roc, I honestly don’t know. It is supposed to turn the A/C off at WOT. But the problem I have is with the function switch.

  4. #4
    Moderator wraithracing's Avatar
    Join Date
    Jun 2010
    Location
    Grand Junction, CO/RR TX
    Posts
    14,206

    Default

    When you say it doesn't make consistent contact in A/C mode . . . What doesn't make contact? The whole unit loses power, the unit quits working, the power to the A/C cycling switch and compressor is not consistent?

    As far as the compressor cycling, have you tried jumping the cycling switch on the accumulator? Is there power to one side when the control unit is in A/C mode and the car is running? If so and you jump the cycling switch do you get power to the A/C compressor unit pigtail? If yes, does the clutch engage and the compressor cycle?
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  5. #5

    Default

    Quote Originally Posted by wraithracing View Post
    When you say it doesn't make consistent contact in A/C mode . . . What doesn't make contact? The whole unit loses power, the unit quits working, the power to the A/C cycling switch and compressor is not consistent?

    As far as the compressor cycling, have you tried jumping the cycling switch on the accumulator? Is there power to one side when the control unit is in A/C mode and the car is running? If so and you jump the cycling switch do you get power to the A/C compressor unit pigtail? If yes, does the clutch engage and the compressor cycle?
    wraithracing, sorry I wasn’t more clear. We can jumper to get power to the compressor clutch pigtail, and the compressor clutch engages and the compressor works. But the whole process starts when I put the function switch in the A/C mode (Normal, Max A/C or Defrost). When I started, the connection thru the function switch was largely intermittent. We would get power thru the switch sometimes, but not at other times. We’ve been using contact cleaner and working the switch back and forth, and it’s gotten better; still not 100% of the time, but much improved. The system has been charged, and when charged put out air at 42F.

    My post was specifically about the function switch and whether it can be replaced separately, or does the whole control unit have to be replaced. At this point, I can probably live with it, but if the switch could be replaced, I would consider it.

  6. #6
    FEP Senior Member tbirdman's Avatar
    Join Date
    Dec 2006
    Location
    Middletown, DE
    Posts
    876

    Default

    Sorry if I'm late to the party, but you're talking about the middle selector switch on the panel that moves up and down and selects defrost, AC, Mix, etc., correct?
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  7. #7

    Default

    Quote Originally Posted by tbirdman View Post
    Sorry if I'm late to the party, but you're talking about the middle selector switch on the panel that moves up and down and selects defrost, AC, Mix, etc., correct?
    tbirdman, yes, you are correct.

  8. #8
    FEP Senior Member tbirdman's Avatar
    Join Date
    Dec 2006
    Location
    Middletown, DE
    Posts
    876

    Default

    As far as I know, you can not just replace the lever arm. I know that there was a member here who posted on how he replaced the faceplate a while back, but the two arms, the one that selects the temperature and the one that selects the different functions, are integrated into one mechanism at the back of the control unit.

    And I'm not that electrically inclined, but I don't believe the HVAC functions are actually controlled electrically, but rather by vacuum, which is fed through a harness attached to the back of the control unit and leads to the separate blend doors. But that's just a guess on my part.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  9. #9
    Moderator wraithracing's Avatar
    Join Date
    Jun 2010
    Location
    Grand Junction, CO/RR TX
    Posts
    14,206

    Default

    Tbirdman is partially correct. The center selector lever is both vacuum and electric. As you move the lever up and down it alters the vacuum to the different dashpots that control the different blend doors to direct the air to the specified vents. As you move the lever from off to the A/C section it sends power to the A/C low pressure switch which will activate the compressor clutch if the system pressures are correct. The electrical plug for the center selector switch is at the top of the unit. Normally you can only see the sides where the pigtail connects, but in the pictures below you can see the terminals and the circuit board inside the unit that control the electrical flow.

    Name:  Unit 3.jpg
Views: 175
Size:  181.0 KB

    Name:  Unit 3a.jpg
Views: 173
Size:  145.3 KB

    So to answer your question, no you can't replace the center lever/switch without replacing the whole unit. That is essentially part of the base unit and is not removable or repairable easily. Not saying it can't be taken apart, but it will take time, effort, and care not to destroy it and make it functional again. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  10. #10

    Default

    Quote Originally Posted by tbirdman View Post
    As far as I know, you can not just replace the lever arm. I know that there was a member here who posted on how he replaced the faceplate a while back, but the two arms, the one that selects the temperature and the one that selects the different functions, are integrated into one mechanism at the back of the control unit.

    And I'm not that electrically inclined, but I don't believe the HVAC functions are actually controlled electrically, but rather by vacuum, which is fed through a harness attached to the back of the control unit and leads to the separate blend doors. But that's just a guess on my part.
    Thank you, tbirdman! ��

  11. #11

    Default

    Quote Originally Posted by wraithracing View Post
    Tbirdman is partially correct. The center selector lever is both vacuum and electric. As you move the lever up and down it alters the vacuum to the different dashpots that control the different blend doors to direct the air to the specified vents. As you move the lever from off to the A/C section it sends power to the A/C low pressure switch which will activate the compressor clutch if the system pressures are correct. The electrical plug for the center selector switch is at the top of the unit. Normally you can only see the sides where the pigtail connects, but in the pictures below you can see the terminals and the circuit board inside the unit that control the electrical flow. We

    Name:  Unit 3.jpg
Views: 175
Size:  181.0 KB

    Name:  Unit 3a.jpg
Views: 173
Size:  145.3 KB

    So to answer your question, no you can't replace the center lever/switch without replacing the whole unit. That is essentially part of the base unit and is not removable or repairable easily. Not saying it can't be taken apart, but it will take time, effort, and care not to destroy it and make it functional again. Good Luck!
    Thank you, wraithracing! I suspected as much. My ‘86 GT has about 98,000 miles, but it’s spent a lot of time inside, so the dash pad, instruments and controls look really good. I guess the 12-15 years it wasn’t used caught up with me, causing sporadic performance because of lack of use. The function switch is working better, and the system has been charged with new refrigerant. When it gets hot, I might have to work the lever a bit to get it to work!

  12. #12

    Default

    Just like the picture shows, they break over the years and the connections get spotty. Replaced my daughter's low mileage 1983 version this winter.

    Kenny

  13. #13

    Default

    Quote Originally Posted by mudgepondexpress View Post
    Just like the picture shows, they break over the years and the connections get spotty. Replaced my daughter's low mileage 1983 version this winter.

    Kenny
    Thanks, mudgepondexpress. I guess I need to keep checking on eBay for one from an ‘85 or ‘86, just in case.

  14. #14
    FEP Power Member
    Join Date
    Nov 2007
    Location
    San Mateo, CA
    Posts
    2,271

    Default

    Most likely the reason they break is the cable gets stiff. When pressure is put on it, it snaps. I looked at one a while back and thought a metal bracket could be made to make a repair. I always leave mine on defrost and heat for the winter as the heat cable frees up when warm. Lubing or replacing the cable should not be over looked. Some day we may run out of spares.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert,
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 07 GT500,
    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •