AC questions and opinions

[WarWagon]

Can a bad ac control do this?

No good used parts from the 1 year only 1995 control head disaster.

Although I would suspect the tampered with recirculate door actuator assembly: looks like it's a known control head trouble spot. The technical reference section covers the control head and extensive board level repairs. Have you replaced the blower switch? A bad switch flickers both recirculate and A/C lights.

95-99 HVAC "Control Head" AC light flickers w/ blower off & erratic or no airflow

Thanks to Ignacio (Nacho) Corella for pointing this out. However it needs a better explanation of what is going on. 1995 Control heads are trouble prone and fail in ways beyond this repair. Newer control heads are also troublesome but not as often. 1995-99 will fail by running the AC...

www.thetruckstop.us

 

[dbrannon79]

when I glued the switch on, I replaced it with a new one. the repair I did there was a diode blown on the board in the control that apparently disables the ac with the fan switch is turned to the off position. I bypassed that so the ac button works separately from the blower switch. found a repair guide online somewhere on how to do it.

all the lights in the control will flicker. both the ac and the recirculate along with the illumination when the headlights are on too. jiggling the wires and board in the control will make it stop!

I will have to read up on the links in the thread you posted. I would be more inclined to repair / replace transistors on the board than spend ## on a new one that will fail again! I wonder what the differences are in the 96+ control heads. if one can be converted and made work in the 95.

the vent / floor / defrost knob is very touchy on mine, hot / cold knob seems to work without issues and the blower speed switch works since I had installed the new switch a while back. maybe with all the issues it's time to replace and make better. I've had thoughts of installing extra relays in the dash up by the blower resistor to help take the load off the control unit back when I replaced the blower switch finding a melted pin in the connector.

 

[Will L.]

I really miss the old school controls that were two cables.
So reliable and when the did rust up easy to change. Out here we just removed it and soaked in oil overnight, wiped it off in the morning and had the rig rolling in the first 1/2 hour. Good to go for another decade in salt world or another 40 years here.

 

[dbrannon79]

I know what you mean!

I spent some time searching online and found the repair War Wagon was talking about but with some pics and diagrams for the 96+ I can find these control heads a dime a dozen at the local pick a part yard, but for my 95, not so much. since mine is badly broken, the plastic is very brittle I am wondering if I can convert the wiring to be able to use the newer control unit.

would anyone happen to have some pics, connector pinouts, and diagrams for the 95 control head? I can compare the two and see if there is a chance I can wire in the newer style control making it work. even if I have to make the transistor repairs it would still be way less than spending the $200 for a new 95 unicorn control head!

Here is the link to the repair I found with pics that War Wagon was talking about.

How To Repair GMC CK Series Trucks HVAC Control Unit

GMC CK Series Trucks HVAC Control Unit Repair AC Delco 15-72548 Heater / AC Control By Gawain Tomlinson San Diego, CA Disclaimer: Any use of the information contained in this document is at the user's own risk. The author does not assume any liability for actual or consequential damages...

www.silveradosierra.com

 

[Will L.]

That is the AC Delco 15-72548 Heater AC Control.
If it helps- hummer h1 uses the same head unit for 1996 and first half of 1997.
The 97.5 - 2006 used the next one that did not have the two buttons.

Hummer owners update to the newer one when they can and get rid of the unit you need. Not that there is a problem with the controller or wire system, but the rest of the system in the hummer sucked and the next one worked like 20% better.

 

[dbrannon79]

@Will L. What’s the difference in the newer ones other than not having the ac and recirc buttons? I assume the ac control switch was intertwined with the knobs?

I’m not sure what the part number is for my 95 but it looks the same as the 15-72548 just has three connectors on it. One for the blower and two that come off the circuit. It doesn’t have the side connector like the 96+ does or the ribbon circuit on the back with the removable or replaceable lights.

 

[dbrannon79]

Here is what mine looks like other than the plastic on the back is all broken up. I think it’s the right part number for the 95. I took these photos off of flea bay!! Even RA doesn’t show a Delco one for my truck!

 

[Will L.]

Way better than I can explain it:

HVAC Problems

Hummer hvac problems and how to identify which hvac generation you have.

www.flashoffroad.com

And incase the link in that article doesn’t work in there:

https://www.flashoffroad.com/Maintenance/hvac/imageHVACprob/gmc_ctrlhead.pdf

I was just trying to let you know if searching for parts, that you can look for the hummer ones also - just different year applications. Hummer was behind pickups until the 97.5 hummer model. So yes they just moved the buttons into the dial.

 

[dbrannon79]

@Will L. I noticed in the article that hummers had the electronic controlled heater valve that diverted the water from the core to bypassing it. I wish these trucks had them

one question, in the article they mention the addition of the Ice 32 additive in the ac system. does that really do that much good? especially with the R4 pancake compressors? I had been pondering converting the system to use the envirosafe refrigerant that is supposedly a blend of butane and propane once I replace the air box and dash, but if the ice 32 really does what they claim, maybe I won't need to convert.

the thing I have had issues with in the past was with the envirosafe is the pressures are generally lower on both hi and lo sides and since these systems use pressure cycle switches that aren't adjustable, they don't cool right on the freeway or when the outside temps are cooler. for my 95 the clutch cycle switch has metric thread that stops me from installing an older style switch that allows for adjustment. for older systems that were ether R12 or the early R134 systems, I never had this issue and they cooled just as well as the old R12 did sometimes even better!

if going that route, I'm not sure if the dryer can be replaced with a different one using standard thread ports. not sure what the evap port or the hose port threads are, metric or standard.

 

[MrMarty51]

Here is what mine looks like other than the plastic on the back is all broken up. I think it’s the right part number for the 95. I took these photos off of flea bay!! Even RA doesn’t show a Delco one for my truck!

View attachment 75808
View attachment 75809

That top pic looks very similar to the control unit that the 2000 truck has. The only difference is the buttons for the AC and recirc are on the top.

 

[Will L.]

Idk what is better, electric or vacuum. Best is a cable.

As to the refrigerant I alw run the original stuff. When r12 became impossible to find i might have known a guy...
But those days are gone now.

Next year biden will probably outlaw all of it anyways.

 

[dbrannon79]

Idk what is better, electric or vacuum. Best is a cable.

As to the refrigerant I alw run the original stuff. When r12 became impossible to find i might have known a guy...
But those days are gone now.

Next year biden will probably outlaw all of it anyways.

I could attempt the cable conversion but that would be an undertaking for me! I will study the diagram for my truck and look for one on a 96 / 97 and see if the newer electronic unit can be made to work. I feel like there isn't that much difference between the two. maybe different actuator motors are used on the 96. if that's the case it shouldn't be too much of an issue since when I replace the box I plan to install all new motors anyway.

lol Biden can't stop the hillbilly in us haha!!

 

[dbrannon79]

I have a wire diagram for a 95 tahoe but nothing for the trucks. I'm starting to search online for the 95 model and 96 to compare, would anyone have them for the trucks in there records to share or possibly point me in the right direction? mainly for the ac system for this project but I'd love to find the complete diagrams for the vin f 6.5 for both years.

the one I have on the tahoe shows the recirc motor having three wires. the motor in my truck only has two, that I know since I just had it out and replaced the gear in it. so I know there must be a difference in them.

 

[dbrannon79]

I found some diagrams on DP from the service manuals for both 95 and 97 year models. the connectors are different but looks like they use the same wire colors and same number wires. the diagram for the 97 is spread out between several sections, blower, air delivery, temp, and compressor control where the 95 diagram is on two pages and simple. I will see if I can put the different sections together as best as I can on few pages and compare them. I think it will just be a matter of scavenging a newer control and the connectors. using the connectors from the 97 harness and the ends on my current control to create a conversion harness to plug in without having to butcher the harness in my dash making a direct plug and play conversion! this will same me some money

 

[dbrannon79]

Well guys it was a success! I officially converted my 95 truck from the 15-72267 control to use the 15-72548 control from a 97 truck. went to the Wrench-A-Part yard this morning and found one along with snipping the harness pigtails for it. while looking at the wires on each controller and the harness in my dash, I discovered the diagrams didn't have all the colors right! it took some poking and prodding around with trial and error to get everything working.

I ended up using the blower switch from my 95 controller since I couldn't get any of the fan speeds to work with the junk yard one. also re-used the blower harness from my old controller since I kept the old switch. didn't have to replace any of the dash door motors ether. once I figured out the wires, everything works. even turns off the compressor when you turn the blower off now

Here are some photos of the two controllers and of the my truck harness along with the finished product. after soldering all the wires up and heat shrinking everything and installed.

 

[dbrannon79]

Just learned there is a 10 photo limit per post. her are the rest... And for the record, before someone asks lol the connections I made with the wires pushed into pins was just while I was testing and making sure I had the right ones connected. I clipped all of the mess out and soldered everything up nicely then taped over them shown in the second to last photo. Also did not make any cuts or butchering on the dash harness, if I need to replace or do any future repairs, it can be disconnected using the factory plugs

 

[dbrannon79]

only item I forgot to snag at the junk yard was a cubbie hole to install where the cd player was. I get that next time I go and have it ready for when I install the new dash I have in the garage.

the funny part is before I did this. when I touched the knob for the floor / vent / defraust. you would hear a "zippp-thunk" when the mode door moved. now its quiet and changes flawlessly! so does the recirc door.

 

[Will L.]

Would be a good spot for flat panel holding digital read out for fuel pressure and turbo boost units, usb charger points, etc. Also a good spot to put the button George Jetson used to make it fold into a briefcase, but those are probably out of stock currently.