89 Blazer defrost controls

[ranger8575]

I have a full sized 89 Chevy Blazer. Two problems - first, the air from the heater is not very hot. I think probably I need a new heater core to solve this problem but I'm not for sure. My major problem is that I can't get the vents to switch to defrost. They are stuck in one position. I would appreciate any thoughts on what I need to do. Thanks

 

[toomany]

There is a good chance the two problems are related. The valve that diverts the air may be broken/stuck/disconected. Allowing cold air to mix with the hot air, causing the not so hot heater. The valve is controled by vacuum. I'm not exactly sure how the whole system works, I've never had work on mine. Unless you're lossing coolant from the core, I would look into this first. I'm sure someone else who knows more about the system will chime in soon.

 

[Brodie]

There is a link on the top of the heater box that connects the AC inlet to the vent outlet. The actuator that it hooks up to is VERY prone to breaking the plastic mounting tab (pull off the vent duct on the front of the box to check it out). If that link can't move you will have the exact problem you are talking about. Let me know if this isn't it. I've had my entire heater box completely apart more times than I care to admit...

 

[ranger8575]

I hate to admit my lack of knowledge but what are you refering to when you say the "heater box"? Is this under the hood or under the dash? Thanks for your help and I will give it a try as soon as I understand what the heater box is.
Thanks again,

 

[ranger8575]

I have tried to check the vacuum hoses that I can find but unless there is one that is hidden, I can't find any problem hose.
Thanks for your help.

 

[4X4HIGH]

The "heater box" is also called the "suitcase" and is under the dash and is what contains all of the heat/AC components. There are vacuum lines under the dash that can break or fall off. Like someone already said both of your problems are no doubt related to one another.

If you need to pull the "heater box" i would suggest just replacing the heater core regardless of if it's good or not since it would definately be the time to do it. If things happen to you like they do me, Murphy would be right there messing you all up.

 

[ranger8575]

The "heater box" is also called the "suitcase" and is under the dash and is what contains all of the heat/AC components. There are vacuum lines under the dash that can break or fall off. Like someone already said both of your problems are no doubt related to one another.

If you need to pull the "heater box" i would suggest just replacing the heater core regardless of if it's good or not since it would definately be the time to do it. If things happen to you like they do me, Murphy would be right there messing you all up.

Will I need to pull the dash to get to the heater box? Thanks for the help.

 

[4X4HIGH]

You do not have to pull the dash but you will have to remove the glovebox and the lower heater duct tube that goes to the driverside heater vent. There is also a bolt that is kind of hidden under the hood and GM claims you have to remove the fenderwell to get at it but i had success using a 1/4" drive socket with swivel and extention.

 

[Brodie]

No. The only pain in the arse is that you have to pull the passenger side inner fender (about 10 bolts) and the battery tray to get to one of the nuts on the bottom.

There should be 3 vaccum hoses going into the box: one at the left(driver's side) end (defrost, heater), and two in the back center that go into the same actuator. There is also one that goes to the floor vent on the passenger side (as well as a T-fitting that goes to the Plenum valve under the wiper cowl)

My advice is to pull the glove box out and remove the duct attached to the front of the box and have a look at the flap in there. It should move freely and be able to close the whole way. (check the plastic clip attached to the flap) Also make sure that the link on the top of the box is hooked up. They are known to strip out the plastic bushing and not be able to shut the flap too. It looks just like a stick off all-thread.

 

[ranger8575]

Thanks to everyone for your help. As soon as I can get some decent weather I will give your suggests a try. Each of you have been extremely helpful. Thanks again and Merry Christmas.