How to: 88-94 climate control LED swap

[Macfluke]

So I swapped my 1989's HVA/C control module for one from a '93 to gain the "MAX A/C" button. It works fine & dandy except for the lights, all of them appear to be burned out. I'm not looking for LED's, just stock replacements. Anyone know what the part number is? Or should I order these:
https://www.taninautoelectronix.com/4mm-14-volt-automotive-light-bulbs-p/4mm14v.htm

by saying "It works fine & dandy except for the lights" are you saying all of the controls and AC MAX button worked perfect? the reason I ask is because I tried that swap a few years back with NO success... I used a known good unit from a friends truck and when installed it did a light show and nothing worked, my friend thought I had burned up the unit but it worked fine when he put it back in his truck...

 

[ima93chevyguy]

So I swapped my 1989's HVA/C control module for one from a '93 to gain the "MAX A/C" button. It works fine & dandy except for the lights, all of them appear to be burned out. I'm not looking for LED's, just stock replacements. Anyone know what the part number is? Or should I order these:
https://www.taninautoelectronix.com/4mm-14-volt-automotive-light-bulbs-p/4mm14v.htm

https://www.ebay.com/itm/4Pcs-Warm-...ash=item3d1fd9eac6:g:IX4AAOSwOMdZQzim&vxp=mtr

I can't verify that these are 4mm but this is basically what you're looking for

 

[DerekTheGreat]

by saying "It works fine & dandy except for the lights" are you saying all of the controls and AC MAX button worked perfect? the reason I ask is because I tried that swap a few years back with NO success... I used a known good unit from a friends truck and when installed it did a light show and nothing worked, my friend thought I had burned up the unit but it worked fine when he put it back in his truck...

Yep, everything works like the old one did, even the "new" max A/C button. What year is your truck? We used to have an '88 and I tried the same swap with a different module and that didn't work. It did at first but then the vent position indicators started flashing and it stopped responding. Interesting to note that most of the wires for that '88 going into that module were white & thicker, like vacuum lines. Before I unplugged the wiring harness that's what I thought they were, like some hybrid unit. On this '89, none of the wires for the truck's harness are white, but none of them matched the wires for the '93 module so initially I didn't expect this swap to work either. Could be why the illumination lights don't work either, as I find it hard to believe all three bulbs are burned out. I won't know until I get the thing apart again & bench test it with that donor harness, man am I glad I take those.

Anyway, I think the trick to the swap is to do the ole Nintendo trick- as in clean the contacts really well with alcohol and also clean the pins of the harness the best you can. I then put dielectric schmoo in the harness before plugging it in to test. Then I flipped the key on, let the unit power up, moved the temp all the way to hot (as it was with the old one) then turned it to defrost and low blow speed. Heard electrical servo motors move. When they stopped, I cycled to floor. Then cycled the temp setting to max cold. Noticed display changed faster than old unit but no longer did the "hold 3 seconds and it'll automatically go full tilt heat/cold". From here I tried every other position too, no flaws or problems. My old '88 would have started flashing a light show by then. So I figured it was good, pondered about the illumination lights but mistakenly assumed that since everything else worked that those would too so put it all back together..

Also, while it may not matter I previously turned the old unit to "Off" and it was at the max heat setting before I removed it (with key off as well).

I am not sure why the swap worked in this '89 but not in our '88. Perhaps the module senses servo feedback or position of them and the older ones aren't compatible.. I did have to swap the blend door servo motor by the gas pedal on the '89 and it came from a newer truck too. Our '88 only had 66k miles on it and it sat for at least a good decade so perhaps things were too stiff for updated module's liking. Not sure..

https://www.ebay.com/itm/4Pcs-Warm-...ash=item3d1fd9eac6:g:IX4AAOSwOMdZQzim&vxp=mtr

I can't verify that these are 4mm but this is basically what you're looking for

Hmm, those look too wide.. The ones in it are narrower. Worst case scenario if all three bulbs are indeed burned out I'll try and swap the ones from my old unit over to this one. I'll bench test it first since I have a spare harness to test it with.

 

[Macfluke]

Yep, everything works like the old one did, even the "new" max A/C button. What year is your truck?

I have a 89 C1500... and having no Recir/Max button has been one of the most annoying things about the truck that I haven't been able to fix and i've even thought of doing a little re-wire and install a button on the dash to somewhat fix this issue but I really hate doing that type of thing so I haven't...
Keep us updated on your quest for success. Thanks DTG...

 

[DerekTheGreat]

Hmm, when was your truck built? Ours was built some time in or after April of '89. That or the HVA/C control module was replaced at some point later as it was dated April of '89. Maybe they did a mid year change or something, what color are your wires for your module? I'll take pics of mine this weekend, too bad I don't have a pic of the old '88. Perhaps you could try another module along with an updated servo motor for poop & laughter. I did notice that the shaft was rather easy to spin by hand without the motor installed, that and I also shot ATF in there to lube it.

Not having control of Recirc/MAX A/C is a major pain for me too, glad it works just hope I don't have to deal with a work around for the illumination side. If anything & hopefully that'll be just swapping a few pins around in the harness if it's not the bulbs..

According to the service manual for my '88, they do have recirc capability and it is supposed to be automatic. So perhaps in the meantime you can set the indicator to full cold & use a lower fan speed to force it to hold recirc. I'm not sure what the thing looks at to keep it in recirc though. That is what I do to manipulate the recirc function on my Town Car. Whole other set up though..

 

[Macfluke]

when was your truck built? what color are your wires for your module?
According to the service manual for my '88, they do have recirc capability and it is supposed to be automatic.

not sure of the exact build date, where would I find that info?
i'll have to pull the module to check the wire colors, maybe this weekend if I have time...

My Owners Manual says "The system will automatically determine if it needs recirculated or outside air." and the system does a piss poor job on determining when recirculated air is needed like in bumper to bumper traffic and the system determines I need to choke on exhaust fumes of outside air instead of recirculated air...


Send from my Commodore 64 using 300 Baud Modem.

 

[DerekTheGreat]

I'm not sure on that one, maybe the RPO sticker in the glovebox. But, the HVAC module has a sticker on top (unless yours wore away) that is dated. Mine had "April 1989" stamped on it.

Yep, that's what I remember reading. Don't forget cigarette smoke! I think that's the most irritating for me, sucks that **** right in..

I did notice this morning that my panel is responding the lights being turned on, the display dims and adjusts with the knob on the dash so that could be a good sign for me. Maybe I just need bulbs after all. I am now having problems with the temp change controls, they'll start to flash after 20 seconds or so if I try to go full cold with them. I don't always hear the motor working and it's rather loud when it does. I'll be replacing that sometime soon. Or I could go back to the old head unit, that seems to work..

update: I did some digging and found the original GM part numbers for the standard bulbs:
021181
1#16081218 <<<<< part #...?
GR.9.276 LAMP-W
(JAPAN) <<<< WTF?

This was ripped right from chevytrucks.com or whatever from a nice write up by SoG. However, the bulb info is pretty much useless as I can't find any in stock anywhere or an equivalent except for this site: http://oemcats.com/oem-parts/16081218.html
Has anyone used these guys? Seems kinda shady.

 

[jus10inbrla]

Just wondering, does anyone know what size those screws are holding the back plate in? I used a pair of needlenose to unscrew them.. and go ba k in


also, what color blue acrylic? I ordered navy it was too dark

 

[bc-chris]

Just wondering, does anyone know what size those screws are holding the back plate in? I used a pair of needlenose to unscrew them.. and go ba k in


also, what color blue acrylic? I ordered navy it was too dark

when i did mine i just used some thin clear plexiglass and in behind it is a piece of blue "gel" that a buddy of mine gave me. the "gel" is the tinted film that is used in the lighting industry to tint old school pot/spot lights

this is the "gel" stuff i'm talking about (i think i used 2-3 layers of it to get the blue the tint that i wanted)...

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and the result...

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[jus10inbrla]

I made a few if anyone wants one