Heat A/C duct work help

[wildweaselmi]

Hey Everyone,
I've been dealing with not having air flow working inside my 91 K5 since I've owned it years and years ago which isn't typically a big deal since I like cruising with the windows down anyhow. Well my wife got leukemia (blood cancer) in Feb 2020 and so the chemo and bone marrow transplant has her over heating all the time or freezing cold so I have to figure this out.

I could feel hot but just radiates (nothing blowing and yet I can hear the blower mode change speeds as I change the fan on the cluster. I really think its a duct work issue or possibly vaccum but not positive.
NOTE: if anyone knows how to fix it and lives in Michigan, I'd be happy to give you some greenbacks to get this fixed the way its suppose to work.

Here is a quick video of what I have so far (just started tonight) .. Any help is much appreciated.

 

[Wes Harden]

First thing is check under the hood there should be a vacuum line on passenger side of engine that either goes to a vacuum reservoir and then through the fire wall. Or stright through the fire wall with a check valve. This vacuum line is probably broken, and or plugged off.
All the doors in the plenum are controlled by vacuum, except possibly the temp door that might cable, it is on earlier squares idk if or when it changed.
If you feel air flow at the defroster duck in the dash, the blower motor is doing it's thing. Need to figure out where the vacuum signals. If no air at flow defroster the squirrel cage may be broken.

Thoughts and Prayers. Hope you get this solved, just for the minor comfort it may provide your wife.

 

[wildweaselmi]

Thank You Wes.. I'm going to see if I can see the vacuum line coming in tonight after work. Will attempt at keeping this post updated for anyone in the future with similar problem.

 

[wildweaselmi]

Working on figuring out the blower motor and why its not coming on. I pulled the blower motor out and hooked up the terminal (that had a purple wire) to the battery and it spun (glad I didn’t loose any important fingers)


So moving onto the relay.. could the relay be bad or possibly just the connector. Ordered replacements from partsgeek since I’m at a loss

 

[85-K5Blazer]

Your wiring harness going into the relay could be the problem. Mine stops intermittently and I turn off the switch and back on and the fan resumes. Everything on mine is new. Switch, relay, fan, etc. When I had someone wiggle the wires going into the harness it stopped and resumed when the wiggled them again.

Be sure the Ground Wire going to the firewall is clean and tight. Not sure if that is an issue, but something to check.

You could "Unpin" the wiring going into the harness house and clean the leads or replace the harness end with splicing on.

They make replacement harness ends as you may have already ordered from Partsgeek.

https://www.amazon.com/Four-Seasons-37202-Harness-Connector/dp/B000CL3LYY

 

[frankin5]

He needs to fix the broken white plastic part. That door is not functional. That is a very common failure for no heat or air.

 

[wildweaselmi]

Your wiring harness going into the relay could be the problem. Mine stops intermittently and I turn off the switch and back on and the fan resumes. Everything on mine is new. Switch, relay, fan, etc. When I had someone wiggle the wires going into the harness it stopped and resumed when the wiggled them again.

Be sure the Ground Wire going to the firewall is clean and tight. Not sure if that is an issue, but something to check.

You could "Unpin" the wiring going into the harness house and clean the leads or replace the harness end with splicing on.

They make replacement harness ends as you may have already ordered from Partsgeek.

https://www.amazon.com/Four-Seasons-37202-Harness-Connector/dp/B000CL3LYY

View attachment 446704

Yea I ordered this so we’ll see

He needs to fix the broken white plastic part. That door is not functional. That is a very common failure for no heat or air.

Yea I saw that and not sure how to fix that. Is it just a screw or is there some special retainer? Would love to see a picture or a part of what I need to do to fix that.

 

[85-K5Blazer]

As for replacement, search the videos on the internet ... I believe you have to have the Heater Box out.

LMC Truck offers the Blend Door Clip P/N 32-2489 1st Picture

I also used a shop of Florida to rebuild my heater box and they sell the part as aluminum I believe .. See Ebay

The Part Guy - Ebay add 2nd Picture

For GM A/C HEATER BOX BLEND AIR DOOR CLIP AC Air Conditioning For Camaro C10 K10 | eBay

Find many great new & used options and get the best deals for For GM A/C HEATER BOX BLEND AIR DOOR CLIP AC Air Conditioning For Camaro C10 K10 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Wes Harden]

That piece maybe broken mine was. But I had air and heat.
Since the blower motor isn't working in the truck definitely need to solve before moving on.

The Purple wire needs to be 12ga wire to motor, the red wire also 12ga is hot at all times, the blue wire is the lower fan speeds from resistor block. If you have selected anything but High or off the blue wire should have power at below 12v. The Blue wire is normally closed path to blower motor through relay. The orange wire powers the relay coil and closes the high blower circuit.


Looking at your relay plug I can see there has been high amp draw on the purple wire. This could be a worn out blower motor, bad ground, or dirty tarnished corroded purple wire connections. I am will to bet the purple terminal is loose and tarnished, and needs attention.
The wire loom and plug above is handy, but the 2 12ga circuits have the wrong size wire. The terminals can be purchased, Packard type 56 female, they come in 12ga size and 16-14 size you need both if you wish to rewire.
With key on select low fan check for voltage on tan wire at resistor block. If you have voltage check the blue wire at resistor block, should a lower voltage. The blue should be same voltage at relay, both terminals blue ,and purple. If this what you find then the wiring to relay is working as designed.
Place the fan switch at High the orange wire at relay should show 12v and the purple wire should show the same voltage. If no voltage the relay is bad, if lower voltage the relay has dirty contacts and creating resistance. Either of those results replace relay.
to check the resistor block test the voltage at the blue wire in low and medium, if they are different and below 12v it is working. No voltage in high or off on blue wire.

I repaired my blend plastic block, I would have replaced had I known I needed it. the metal 1 posted above is sweet.
broken

repaired


Good luck let us know your findings

 

[wildweaselmi]

replaced the relay and the plug but no luck. still no blower motor activity unless i go direct to tang on blower motor.
Guessing it must be at the controls. i followed the diagram provided at the plug/relay and i never get power to any of the other leads besides the red wire which is always hot. So my logic says you gotta go to the source (assumption it’s the control which LMC is out of)
I also saw two spots that look like a vacuum line should be plugged in and isn’t but not finding it so i’m digging around for it

 

[Wes Harden]

With any mode selected (heat, ac, vent) does the brown with white have power going into fan switch ? If not doe the brown wire at selector switch have power?
@kennyw got any 91 havc controls ?

The one used vac nipple is plugged, if you look closely. I think the lines are good the rotary vacuum switch may not hold or path vacuum correctly. Even if it didn't you should still have air flow at the dash vents with a working blower system.

 

[85-K5Blazer]

Sounds like your Fan Switch or selection mode switch is out.

I bought the fan switches from RockAuto and the Mode Switch from Amazon.

Blower / Fan Switch - Four Seasons 35990
Mode Switch - Four Seasons 36695

I see yours is a 91 and mine is an 85, I suspect they will be the same number ... Use the Four Seasons Electronic Catalog and research.

As for the open ports, they are plugged internally. You should have five vacuum lines coming from the manifold which has six ports besides the two open holes for the posts to come through. One is intentionally plugged.

Hope this helps !

 

[wildweaselmi]

thanks for all the replies. great community for sure!
i just finished verifying all wires are connected and not shorted (just used a multimeter connected to each end (with a few jumpers))

I have to agree I believe it’s the selector switch and or the blower switch since all the wiring “appears” to be good.

time to go find some replacement parts to see if that fixes it. even with all these parts it’s way cheaper then even one part on my new vehicle so no complaining here

 

[Wes Harden]

check those wires make you have power there. easy with multi meter.

 

[wildweaselmi]

check those wires make you have power there. easy with multi meter.

yea i used the most excellent diagram you provided earlier and traced each one (at least fairly confident i got them all). Everything is good. I was assuming could of been an issue with the plug on the firewall but all signs point to all good which leads me to believe the heater control is no good which could also be why defrost, vent, etc isn’t working but we’ll see. right now i just need blower motor to turn on when i ask it to.. comes in handy when i need defrost to see where i’m going.
will keep u all in the loop

 

[Wes Harden]

If you provide a fused keyed hot to brown/white wire at fan switch (64) you should have a working fan that will have all 3 speeds.

 

[wildweaselmi]

If you provide a fused keyed hot to brown/white wire at fan switch (64) you should have a working fan that will have all 3 speeds.

Super Props to Wes
I did confirm I have power at BRN [50] with key turned to on and if I jumper from [50] at the selector connector to [64] I have blower motor functioning levels M1, M2 and HI so it feels as though I'm correct assuming the heater control switch is bad??

I ordered a reconditioned one off eBay for $75 since LMC is backordered and they have no idea when. I checked with a few others and they are all sold out as well. I found some less expensive ones on eBay but they looked like they dug them out of a graveyard so I passed since I don't to have to replace it again. I like the once and done approach. Do it right one time and don't worry about it, especially when you are on a trail in the middle of nowhere by yourself.

I'll keep you posted when my new part arrives sometime end of this month (hopefully in time for some memorial weekend trail riding)

 

[wildweaselmi]

I went all out because I wasn't positive it was making it through the selector (from [50] to [64] -- which I could of tested but didn't). I also ordered it before I saw Wes suggestion for jumping from [50] to [64] to verify blower was good. So typical knee jerk reaction is replace the entire thing... not so good of a plan but figured it couldn't hurt.

 

[85-K5Blazer]

I deleted my post as I thought about it and realized that if you replaced both the Selector Switch and the fan switch you would be in around $75.00 on your unit if these switches were changed out ... the knobs just pulls straight off and pushes back on.

Let us know how it turns out ...
Thanks,

EDIT 1: That is a good looking unit ... better than some I have seen on E-Bay ... I would consider buying the replacement switches and putting new switches on the unit and then be truly done with it.

 

[wildweaselmi]

okay replacement heater control installed and blower works, hot/cold works, selector doesn’t seem to work. no difference between defrost, heater, vent.
i’m assuming this could be vacuum issue.
i traced the source vacuum line coming in on passenger side from right side of carb.

i know this is a long shot but does anyone know how much vacuum pressure must exist for the vents to work?

going to get a vacuum pressure gauge to see how much vacuum is at carb and start working my way back