Luke warm at best.

[BohdiAstro]

Initially I replaced the thermostat and that did nothing, then I replaced all the vacuum lines according to the diagram on the gen2 post, radiator is full, not sure which direction to look at this point could he switch be bad? The vet control switches vents as it should. Temperature control seems to work fine its just when I turn the heat on full it's blowing 65 degree air if I turn it to cold it blows 30 degree air. Any diagrams would help, I can follow those alright, where is that small switch with the gears people have had break at? If I flush my entire cooling system will that flush the heater core as well? How is ould I go about only flushing the pump

[The Drummer]

You may clean the heater core via the hoses ,top left when facing the van, the actuator door module is by the heater core ,i do think you need to remove the dog house , there are numerous treads about this in here.

[townboy62]

I had same thing about a month ago. tried flushing my heater core but didn't seem to get a good flow afterwards, so I replaced it. Almost blows too hot now!!
after inspecting the old core it looks like someone, at some point put radiator stop leak in...really, really worked to stop up the heater core!

[townboy62]

by the way I have a 2002 RWD and the heater core was simple to replace. In the foot well of the passenger side. Hope yours is a later model, I hear the earlier ones are a bear to change.

[DRZ]

One thing all of us not living next door to Lumpy should do is to take the restricted heater hose fitting at the engine out and replace it with an open one to speed up the flow of water through the heater core. The job of the heater core is totally different from the engine radiator where you want the water to take a long time to get through it as then the passing air can take heat out of the water. With the heater core you want the water moving at a high rate of speed to hold down the heat losses in the core and hoses. The restriction was placed there because it is less of a problem for GM if you freeze in the cold than your engine maybe over heats in the desert.

[five10freak]

I had a similar problem of luke warm air in my 99 lt. After chasing this thing for more than a year, the problem and solution kinda fell in my lap . In my case the previous owner must have replaced the heater core and not place it in it's proper location as well as not putting the two retaining clips back on, FYI when I bought the van the said clips were in the storage drawer under the passenger seat, but I just didn't know thats what they were when I found them.

How I figured out my no heat problem was one day messing around trying to figure it out I pulled on the heater core hoses at the firewall and they moved outward almost 3 inches. With a buddies help, we took off the access cover for the heater core, I had him pull on the heater hoses like I did and rechecked the heat output. almost instantly the heat went from 55-60 degree air to 135-145 degree air.

Basically with the heater core sitting too far down in the case the air was being bypassed somehow and getting mixed with outside air. So what I did was to loosen both heater core hoses push the heater core back up and used the retaining clips to hold the core in it's proper location then pushed the hoses farther up the pipes. Secured everything and rechecked. I have had blazing hot heat since then, a happy camper now.

Now if I could only figure out my rear heat,LOL

[BohdiAstro]

It's strange, even after replacing all of the vaccum lines I still hear a vaccum whistle from time to time, planning on flushing the heater we core, and I grapped an actuator just in case. Hopefully it's one or the other and not both. Should there be any sounds when switching from hot to cold, the switch isn't as"firm" as my 99 Silverado. Snows coming down z gotta get this heat blowing!

[bubbalowe]

There is a coolant diverter valve inside the passenger side front fender. Its purpose is to direct coolant around the heater core whenever the air conditioner is on.

[redfury]

what is the temp on the hoses going in and coming out? They should be approximately the same temp. If one is colder than the other, you have a restricted heater core.

[BohdiAstro]

So I replaced the heater core and still having Luke warm heat. Where exactly is the air blend actuator, I've dug around on here and seen passenger side, looked for it during the heater core swap and didn't see it. I have a 2005 astro

[BohdiAstro]

I had the hot cold issue with the lines going into the heater core, flushed it , nasty business, and still had hot cold lines, swapped the heater core and have equal temperature lines but the only thing left is the blend door actuator, which I can't seem to locate

[BohdiAstro]

Drove it down the road, thermostat kicked on and got my face melted by 165 degree heat. Heater core was problem.

[BohdiAstro]

but why didn't it work sooner, water pump?

[kennysmoke]

You might have had an air lock and it finally burped the air out. Just my guess.

[Leeann_93]

The heater core is pretty high. If you don't put the passenger front wheel up in the air when you do about 3 burp cycles, you're not going to burp out all the air without further help.

It's just a PITA fact on these trucks.