i replaced my heater core heat works great coming out of the bottom vent that is, for some odd reason cold air blows out the top vents and hot from the bottom vent, i have the a/c/heater controls set to heater and the slider to hot and it does this, i've tried switchin between vent and heater and they both blow at the same time no matter what, before i did the heater core change i used vent so some hot air would come from the top but now nothing, anyone have any ideas to this very weird condition, i dont even know how its possible to be blowing hot and cold from different vents at the same time,

 

It sounds like you have inadvertently knocked off one of the vacuum hoses that controls the HVAC system.

 

i checked all the vacuum hoses and their all good

 

Go to main vac line at fire wall Blow cigarette smoke into car & have buddy of yours watch for Smoke while changing modes Guaranteed If vac is problem ( put smokes in tool box 4 next time) HAZARD ! DO Not Buy Lighter or wear shirt with pocket

 

hmm ill give it a try as im a smoker :-D

 

Just did a similar repair on my '97 LSS (88) and used the factory repair manual to trouble shoot the problem. (blend door motor) Saved a bundle by not going to the dealer and it works great.

 

Glad you fixed your problem, but the 77-90 B-body cars use vacuum diaphragms to switch between floor, dash, and defrost vents. If you lose vacuum, the system defaults to floor and defrost flow. Temperature is controlled by a single heater blend door, located behind the glovebox. A cable actuates this door, except on cars with Tempmatic. In that case the cable sets the temp on the Tempmatic unit and the unit automatically moves the blend door.

 

A few more thoughts. First, ALL of the vacuum actuators and associated airflow control doors on the HVAC system are on the passenger side of the firewall. The heater core is on the engine side of the firewall. Unless you did something very strange while changing out the heater core, you should not have even been close to the actuators or doors. On the other hand, the vacuum hoses that feed the HVAC system all run right over and around the HVAC box on the engine side of the firewall. There should be a vacuum storage ball strapped to the HVAC box. It is highly likely that one of these was disturbed during heater core changeout.

 

vacuum storage ball? wow theres a lot of crap i gotta check haha, i did notice that the main vac. line comes from the engine to the heater system maybe i should try replacing all the engine vacuum lines and see what happens

 

Take a breath. If it worked before and doesn't work now, clearly you disturbed something while changing the heater core. If you have money to burn, feel free to replace the lines. I'm cheap, so I like to diagnose the problem before throwing money at it.

 

haha i dont blame ya i dont like spending money neither, every dollar i save goes in the gas tank tho lol. but the cars old and the vac lines probably havent been replaced in years so its about that time, there is a door behind the heater core against the firewall that opens to let hot air in but thats working fine, so im thinking its a valve door on the inside of the car under the dash somewhere so thats a day job to mess with i just wish someone else has the same prob and figured it out how to fix, but i'll probably fix it without even trying

 

well i found out the problem, it was the heater core, for one the one i got from advance auto parts is different from the original (a bit wider, no valley between the inlet and outlet on top like my original has) anyway it was blocking one of the doors from opening all the way, and it also was leaking at the fittings found a big puddle underneath the car this morning, store said it might be the wrong heater core and ordered me a new one lets hope its the right one i get it in the morning

 

just an update got the heater core the store ordered its the right one, fits like a glove, heat works amazing and no more hot and cold air at the same time, the top vent and bottom blow hot like it should thanks for all the help guys

 

Glad you got it fixed. It stinks that you wated so much time to their mistake.
Moral of the story - always take the old part with you to the store when you buy a new one (or pick it up when it is ordered) to see if it matches up just right, side by side.

On these older cars, I have seen many mixups from the stores - more than I would like. I know we should trust them and their database, but sorry, I cannot any more.
Worse i have seen is the 86 Cutlass Supreme - they often get the little FWD cars confused with the RWDs.

 

exactly well i usually bring in the old part but since i didnt have a car to borrow to take to the store i had to use mine, yea just like with my heater control valve mine is the metal vacuum activated one i had them look it up and they only had the plastic different kind of control valve, atleast the girl at the register was cute and she drives an olds too

 

Hi there. I have a 1984 Oldsmobile Delta 88 as well and I had a leaky heater core replaced. My Defrost mode now blows hot to the windshield but cold from front vents. Also my Heater mode blows Hot through bottom, Cold from ventz. Did you notice before if the bottom vents were weaker on the passenger side when you had this issue? Seems like I have the same issues and I'm glad I came across this site. I'm gonna order a new heater core from NAPA and get it installed this week. I'll let you know how it goes...

 

Which one looks like the one thst worked?

http://m.napaonline.com/parts/PartsList.aspx?&t=%3fNtt%3d%26Ntk%3dCategory%26N%3 d599001%2b101984%2b50052%2b2052006%2b4052026%2b599 9999%2b27448%26Ne%3d25000&s=1&p=1

One looks skinnier than the other.

 

Which one looks like the one thst worked?

http://m.napaonline.com/parts/PartsList.aspx&t=%3fNtt%3d%26Ntk%3dCategory%26N%3d 599001%2b101984%2b50052%2b2052006%2b4052026%2b5999 999%2b27448%26Ne%3d25000&s=1&p=1

One looks skinnier than the other.

 

Welp, turnes out they installed the same one I ordered. Spectra Premium 94501. Got my old heater core back and rebuilt at a local radiator shop for 73 dollars. Getting it installed today. Will update when I get my car back.

*Fingers Crossed*

 

After original rebuild heater core all works PERFECTLY!!! nothing better than the OEM part! Seriously to anyone don't use aftermarket Aluminum heater cores in these old boats! It won't (likely) work. And if you do, make sure you get your old heater core back as a backup if the aftermarket fails. No more shitty vent problem.

 

Glad you got it. FYI, you would be better off in the future to just start a new post then a reply to one that is almost 6 years old.