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Thread: HVAC Problem - Suspect Mode Switch

  1. #1
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    HVAC Problem - Suspect Mode Switch

    OK guys, a couple days ago, I finally changed out my stock/OEM butterfly heater control valve (it appeared to be stuck closed and was leaking coolant around the valve's pivot that extends through the valve body) and replaced it with the plastic AutoZone Everco piston heater control valve.

    While I no longer have a coolant leak, I still don't have a working heater.

    Upon diagnosing the problem further I discovered a few things:

    1) the vacuum line that actuates the heater control valve is constantly on when the engine is running, thus my old valve wasn't actually stuck closed but was rather in a state of constant closure due to receiving a constant vacuum from the line;

    2) as the vacuum line is constantly providing vacuum, even my new AutoZone Everco valve is in a state of constant closure thus no coolant is making it to the heater core; and

    3) the HVAC mode switch does not redirect vent flow to the windshield vents when the 'defrost' position is selected, but continues to only blow from the front and door vents.

    I honestly have no idea how long this has been the case with my HVAC system. Who knows, perhaps my A/C could still even be fully charged?

    I believe that the HVAC mode switch needs to be removed and rebuilt, as demonstrated by Steve in his videos, but wanted to be sure before going about doing this that I wasn't missing or over-looking another potential/possible cause of the problem I'm currently experiencing.

    Also, is there a difference with the rebuild kits amongst the vendors, or are they all the same? DMCH (Midwest) has a rebuild kit for $39.95:

    http://store.delorean.com/p-7759-mod...build-kit.aspx

    Is this the best one to go with?

    Thanks for any help/insight that you guys can provide
    "You can never use too much anti-seize!"

    --Josh S.
    #1798

  2. #2
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    OK, just ordered the mode switch rebuild kit from DMC-Midwest, so hopefully that will solve my problems
    "You can never use too much anti-seize!"

    --Josh S.
    #1798

  3. #3
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    Yesterday, I decided to pull and rebuild my HVAC mode switch under the presumption that the rubber diaphragm (maze) was still in decent shape, but just stuck and not rotating with the rest of the switch. As Steve meticulously documented these procedures in a series of 'how to' videos, I didn't bother to take any pics.

    When pulling the mode switch, I chose to go in from the driver's side, as opposed to the passenger's side as Steve did in his video. On my car anyway, the HVAC ducting and AC evaporator/ heater core box are in the way on the passenger's side, thus severely restricting access. Getting the switch out was easy - I didn't even bother removing the fan fail/defrost/lock doors lights from the face plate, as there was plenty of slack present and it made reassembly that much easier.

    Upon taking apart the switch, I noticed that the keyed rubber nubs that hang off the back of the rubber diaphragm (maze) and secure it to the plastic backing plate had been completely sheared off - all but one that was severely bent. But the actual diaphragm (maze) disc appeared to be alright. So, using a sharp tipped nail, I roughed up the surface of the plastic backing plate and applied a decent amount of some all purpose adhesive (Steve complained about adhesive being present on the defective switch he rebuilt in the video, but when you only have one retaining nub left, it's the best solution) that I had on hand. I then affixed the diaphragm (maze) to the keyed plastic backing plate, making sure to properly align the sole remaining nub, and allowed it to sufficiently dry. I then thoroughly removed the excess dried adhesive from the assembly.

    Next, I applied a generous amount of petroleum jelly (Steve used some smelly automotive grease) to the faces of the rubber diaphragm (maze) and the metal port plate, joined the two pieces together and rotated them multiple times in both directions, and then used a q-tip cotton swab and tooth pick to remove the excess petroleum jelly from the walls of the maze and vacuum holes on the metal port plate. I then completed the reassembly of the mode switch.

    As Steve said in the video, putting the switch back in is much more difficult than taking the switch out. Although I was able to get it mounted and the vacuum lines (octopus bundle) reattached without much struggle, I couldn't manage to get the three electrical connectors reattached. Thus, I ended up having to pull the center console (referencing yet another Steve 'how to' video) - it was a royal PIA, but not overly bad. Once the console was out of the way, I was able to easily reattach the three electrical connections to the switch. I also used the opportunity to insulate and isolate the cigar lighter electrical connections in order to prevent future shorts / fuse #17 blowouts. Everything went back together rather smoothly and I was pleased when I didn't have any extra hardware left over at the completion of the job.

    Today, I was finally able to test my repair, and... I'm pleased to report that I now have a fully operational mode switch, heat, and operational air-flow directing (from center/door vents to floor vents to windshield vents)!

    SUCCESS!

    Special thanks to Steve for the great 'how to' videos and Dave S of DMCMW for confirming that my problem was a stuck mode switch, as I had suspected
    "You can never use too much anti-seize!"

    --Josh S.
    #1798

  4. #4
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    I'm working on my HVAC and think this might be my issue as well.

    Can someone help confirm deny if it's the mode switch?

    -The vacuum actuator (with the plastic arm that breaks) is OK, and operational.
    -The center vent flapper thing only opens with the selector on "max."
    -Air blows out the ducts to the doors almost all the time.


    Question: is there a floor heat duct? I saw a foot well vent mentioned on Talk, but I'm not finding one. (I haven't yet really looked extensively.)
    Bro....do you own a DeLorean?


  5. #5
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    I just tested all the modes, hot & cold, and also found the resistor/plate thing on the bottom of the lower evap housing was half-off and a bunch of air was coming out. I fixed that and things seem much better but I still have an issue.


    Max, Norm, and BiLevel: [HEAT setting] Center vent (low flow) and Driver's Door .....[COLD setting] Center Vents & Doors (high flow)

    Vent: [HEAT setting] Center vent (low flow) and Driver's Door .....[COLD setting] Doors (High flow)

    Heater: only blows out the doors on HEAT or COLD setting

    Defrost: [HEAT setting] Windshield (low flow) and Driver's Door .....[COLD setting] Doors


    Observations:
    -No air out the footwell vent on any selection
    -Slight hiss on the Heater selection
    -Defrost seems low-flow.

    I actually don't know what to expect at each setting other than obvious things like Heat, Max, and Defrost.
    Bro....do you own a DeLorean?


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