Hey all!

My heat sucks. I've done a lot to try to fix it but nothing has worked so far. Last fall I tried fixing the issue but haven't succeeded yet. After flushing the heater core and replacing the thermostat I bought a heater treater and verified the blend door actuator still worked. My heat still sucked, so I decided to replace the heater core. Still nothing. I rebuilt my engine (to include replacing the water pump) about a year and a half ago and have put about 5k miles on it since. No change in my heat. Summer comes around and I notice my AC isn't as cold as it used to be. I'm not sure if this is a symptom of whats causing my heat to suck or if I need to recharge the system. I noticed my compressor is always running when the air is on. iirc it used to cycle off and on in previous years. Anyways, that's a separate issue I think.

I've spent a lot of time bleeding the cooling system to make sure there's no air trapped in the heater core. The heater core it's self gets really hot to the touch, so do both hoses coming and going from the heater core. I had the wild vents issue as well but recently fixed it. I replaced the check valves but still had the issue when going up hills and such. I revised the whole vacuum system and replaced the rubber hoses because mine was a mess of old cracked hoses and brittle T ways. Also I added an extra reservoir and problem solved.

I feel like maybe my blend door isn't sealing all the way. I hear the actuator working when changing temps, also i hear it when the door is closed and the motor comes to a stop. I verified the various vent actuators are working also. My fresh air blend door appears to be sealing also. I'm stumped as to what the issue is. Any input would be greatly appreciated.

By the way my truck is a 2001 5.2L quad cab 4X4 with 205k miles.

 

Might be interesting to stick a bore scope into the heater box, and see what the blend door is doing.... Given it doesn't get as hot, or cold, as you think it should, this might be a good place to start.

Aside from that, it is REALLY difficult to get all the air out of the heater core......

Probably wouldn't hurt to check pressures on the a/c system. Compressor running constantly is actually OK.

 

Verify you did the proper re-set to the blend motor when doing the heater treater. After I replaced the core I had instant heat. I've also done everything you've done and I'm at 270k. Also, if you replaced the check valves and it didn't work, you did something wrong or they're junk. Get the AC Delco ones from Amazon. They should look like stockers (half black half yellow) and sold for GM vehicles but they are the right part.

 

I like the bore scope idea. I have a cheap ebay scope. Where would I insert it? Drill a hole? I'll try the fresh air flap tonight If I can get out there. I bought a cheap AC recharge can with a pressure gauge. I'll try to hook it up tomorrow and see what it reads.

I put the blend door motor back on as it was and that was it. I read it will eventually work its self out. I'll have to read up on how to re-set it. Maybe thats my problem. When I change the temps from all the way cool to all the way hot I hear the motor working, then slowdown as the blend door hits the stop inside. I will have to try the bore scope idea HeyYou suggested also.

I did get the AC delco check valves. The black ones. I had them backwards at first but I fixed it recently. But I still had the wild vents when my vacuum dropped down near zero Hg at high throttle input for more than 15 ish seconds. I added the extra vacuum tank and problem solved. I think my plastic vac tank is cracked or something. After I re-did the vacuum system I still had the wild vents until I added the extra vac tank. I might try capping off the factory vac tank and see what happens. Attached are pics of the vacuum distribution block I installed and the home made vacuum tank. A brass hose fitting soldered to an empty propane tank with the valve drilled out. haha I ended up hose clamping it to that cylinder AC component. All the hoses sealed up well. Overall it seems to work well.

 

where are the check valve if you installed that distribution block?

 

It's about 2"-3" away from the inlet on the side of the manifold just like when stock. I can't remember where the second one in the system is off hand but I replaced that one too.

 

I finally got a chance to mess with it some more. I pulled the blend door motor to verify its been adjusted properly. I followed the correct procedure. I remember I had a fitment issue with the heater treater when I first installed it. It didn't want to slide on 100%. I fixed that issue, but my heat still sucks. I manually opened and closed the blend door to confirm it was able to seal correctly to change the air temps. Everything seemed fine. The blend door motor still seems to work fine. I can hear it open and close the door.

I was able to re-confirm the heater core gets really hot on both inlets. I feel like my heat is worse now, also like I'm not getting the same amount of air flow our of the dash vents. Defrost seems to have the same air flow but the temp is still lukewarm. I really hope I don't have a blend door issue, but it's looking like it. I'm going to cut a hole in the air box next to see whats going on. I'm the type I would rather go to the junkyard and pull another HACV box and rebuild that one then swap it in. However that would require me to discharge the AC system.

 

Is the issue the heater core or air flow itself? How did you replace the core. Your typical shade tree yank the broken dash pieces off and drop in a heater core is not the best way to do this. I ALWAYS advise you pull the heater box out and use a genuine mopar or similar type heater core without swivels, had way to many leak and its not a job when done correctly you want to do again. I advise this way for two reasons one its the only way to install an oem type core, also the lack of cabin air filter on these trucks leads to the AC evaporator becoming one. They are always plugged up leaves grass clipping whatever your resident rodent drags around and its just all around gunky muddy junk. Resulting in very little to no air flow. Also resulting in poor cooling and poor heating.

Again as advised above i would definitely verify door operation as well, but something its something else to keep in mind.

 

Heater core gets hot then it's not low heat.
Blend door works by hand and by motor but low air flow.
Blower motor solid?
If so, the only thing left is the hack vacuum setup keeping certain vents closed or blocked.

 

I did the shade tree fix. I hinged the dashboard away from the firewall. I used a Cardone brand heater core iirc. I'm sitting in my truck now on lunch, running the heat. I think the air flow is ok after all. It seemed weak when I was driving into work this morning, but who knows. The temp seems ok right now but it's 61F here. This morning it was 10 or 15 degrees colder and the heat was terrible.

I'm going to re-verify the actuators are actually closing the doors all the way. If nothing changes I'll have to cut a hole to see what I see. The blower motor seems to be working well. Do you know where the fresh air comes in? So I can try to check it for debris.