Poor Heat, Not Sure Where to Start

[57diesel]

Not sure if 99 is the same as 96 and 97 but both of those years had issues with the power feed connection to the blower switch in the dash. Its available as a separate part from the rest of the control panel. They also have a update harness for some insane cost. Possible late in the run or as an update they went to 2 parallel input pins for the power instead of just one. Both of mine had melted the pin and switch pretty bad. Instead of paying for the harness that even the parts guy said was a rip off I soldered a piece of heavier wire direct to the 2 input pins on the new switch and then used a dremel to hog out the damaged area of the connector so I could pass the new wire through the hole and still plug in the rest. I then soldered the new wire to the old one after I cut off all the damaged areas.

[GbByChubsy]

So at the very least I will need to replace blower motor. But what now for the heating? So I attempt a back flush or just cut my losses and take out dash? More so, how do the filtering systems for the air work in these trucks without cabin filters?

[smokydiesel]

Thiers no cabin filter. When u replace the blower motor use a mirror and a flashlight to look up thru the cab to see any birds nests you can also see the cores of the hvac to see if they are plugged on the outside. That should eliminate your airflow problems unless the hvac doors and or servos are broke. Do a 5 min test to check if your hc is plugged with the truck off remove the heater core return line of the upper passenger side of the radiator. then have someone else start the truck and be ready to shut it off. When it starts it should gush out like a garden hose. If it doesn't you hc is plugged.

[GbByChubsy]

I am aware there are not cabin filters. I was asking the process for filtration given there are none.

So, I suppose back flush and see if that helps heat. Blower motor and what exactly do I need to fix the air direction issue? New control panel and ...?

[57diesel]

On the control issue you will have to determine if you have a control issue, motor issue, linkage issue, a physical door issue, or all the above.

The mode door motor and linkage is above the gas pedal. They say never to operate the control motor without it being hooked to a door. Apparently there is some sort of internal position sensor that can over run and wreck a good motor. The mode system is 3 doors. One door has a direct connection to the motor. This connection is a hex or D that only fits one way. The other 2 doors run off of links off this door. You will just have to get a look up there and see if everything appears to still be attached and moving. Most common problem seems to be the upper forward door. Sometimes the crank arm just falls off. Other times the other end of the door falls off its pivot and falls down and jams the other doors. The links are spring loaded so in theory if jammed they wont damage the motor. The links are just attached with plastic clips so they can also just pop off. With the gas pedal removed you get slightly more room to work over there.

[tookielee]

Hope you don't get offended, but you've been asking about this for 6 days....
Backflush takes less than an hour, pulling the blower (at least in the front) and
inspecting the fins is also less than an hour. Do these two things, and go from there.

[GbByChubsy]

Started asking Tuesday later afternoon so I did not get anything done Tuesday. Wednesday I had to do a transmission flush with the time I would have started messing with the heat. Thursday I researched more into the connections with the rear controls to try and find more answers because I did not have time to work on the truck since I would not have it into the evening and on Friday. Friday I did not have the truck due to body working being done on it. That night I bled the system to find air pockets, did not help. Saturday I noticed more problems with air flow so I had to redirect my approach with the new problems, so I looked into an oil leak I had to give myself time. Today I have my approach.

Essentially I am laying my ducks all in a line to go at it one at a time rather than try one thing, wait ask more questions and try again. Blower motor is not my biggest concern now, as it will need to be replaced since it is taking a dump so no reason to inspect it.

[GbByChubsy]

Well, I went to a national repair shop chain today where I know one of the managers, looking to borrow a tool. I end up talking to one of the techs for about 15 min in depth about the issue. He has a gassed but also a 90s burb. We go over things and he says it is the doors period. Based on the fact that some of the vents blow on command and some do not. Therefore cold air will mix with the warm air from the heater cores and result in the reduced heat. It is better while driving he said because of the increased force pushing through the heater core and less so while at a stop. Also aligns to because the AC blows cold but not as cold as it should despite an all new system as you see in my Sig.

More so, he has the same issue with his blower motor on his grand prix. So I took the motor out there and it has seen better days. Advance had a Factory Air one in with a lifetime warranty so I picked it up. Luckily my friend will let the tech work on the truck tomorrow with me so we can tackle the doorrs and I will replace the motor right after.
Ps never went for help at the shop because the guys and my manager friend have no knowledge of diesels but luckily they have a tech good with air!

[57diesel]

Found the thread on fixing my mode doors.

heat ac mode door problems

[JMJNet]

Originally Posted by GbByChubsy

Well, I went to a national repair shop chain today where I know one of the managers, looking to borrow a tool. I end up talking to one of the techs for about 15 min in depth about the issue. He has a gassed but also a 90s burb. We go over things and he says it is the doors period. Based on the fact that some of the vents blow on command and some do not. Therefore cold air will mix with the warm air from the heater cores and result in the reduced heat. It is better while driving he said because of the increased force pushing through the heater core and less so while at a stop. Also aligns to because the AC blows cold but not as cold as it should despite an all new system as you see in my Sig.

More so, he has the same issue with his blower motor on his grand prix. So I took the motor out there and it has seen better days. Advance had a Factory Air one in with a lifetime warranty so I picked it up. Luckily my friend will let the tech work on the truck tomorrow with me so we can tackle the doorrs and I will replace the motor right after.
Ps never went for help at the shop because the guys and my manager friend have no knowledge of diesels but luckily they have a tech good with air!

I think for AC stuff, they probably knows it well since I suspect the AC system are similar amongst GM vehicles.

At least you have somebody that can help you on hand.