Previa heating system troubles

[octane98]

Hi folks !

Lars from Denmark, Europe here !
Just bought a 1992 Previa. Love the car but are having a bit of heating-system trouble.
Wonder if someone might be able to help me.

I'm getting VERY little hot air into the cabin.
The temperature of the air is just fine ( as in hot )
but I just get VERY little of it no matter what I do.

..the blower ( under the hood ) works just fine

IMG_7967.jpg

..took the central/lower dashboard apart and checked the
various control-cables and mechanisms . Couldn't find nothing wrong
( and they all seam to work for adjusting and getting the heat to the screen / to the floor etc. )

IMG_7968.jpg

It's as if there is some restriction / blockage of the airflow somewhere
or maybe something has come loose, so the flow is almost lost somewhere between
the blower and the cabin-outlets.

I do have a Haynes manual, but can't find an overall view/schematic for the complete
heating system .
I did check these drawings from the 'Previa Collision Catalog' provided here on the forum,
but have a hard time figuring out where the problem might be

v1.jpg

v2.jpg

v3.jpg

Any help, guidance or hint would be greatly appreciated.
It's getting freaking cold up here.

Thanks in advance !

[tbkilb01]

Does the fan switch blow low to high through vents when A/C button is turned on? The fan switch working? Does airflow change when you slide A/C climate control levers to heat? Does your previa have a thermostat? You've also a control for 'rear heat' damper that directs air from front vents to the side door vents leading to back seat area to heat the back seat area. It's the top one. Try sliding it to the left. (Less to back area).If the air flow levers are set to up front and air slows down when sliding climate to heat. You may have a problem with heater core. Have you tried the search feature of this site. Works great. Use two words, or search the web using 'Toyotavantech' in search. FSM mentions fuses,switches,water valves,coolant level,heater radiator(core), etc. Mine heats things up fast. Haven't had any problems yet (knock on wood), except that the console lights around A/C levers tend to dim/flash when I slide A/C climate control levers from cool to warm and back. Hope this helps.

[octane98]

Thank you for your reply tbkilb01

Does the fan switch blow low to high through vents when A/C button is turned on?
.. yes

The fan switch working?
..yes

Does airflow change when you slide A/C climate control levers to heat?
..no

Does your previa have a thermostat?
..yes

You've also a control for 'rear heat' damper that directs air from front vents to the side door vents leading to back seat area to heat the back seat area. It's the top one. Try sliding it to the left. (Less to back area).
..no change in flow that I can fell ( difficult when the flow is so feeble )

If the air flow levers are set to up front and air slows down when sliding climate to heat. You may have a problem with heater core.
..I could very well be wrong: but I don't think it's a heater-core problem.
The air-flow is hot allright... it's just the amount/quantity of it that is so very low

Have you tried the search feature of this site. Works great. Use two words, or search the web using 'Toyotavantech' in search.
..yes I did. Couldn't find anything addressing this here problem

FSM mentions fuses,switches,water valves,coolant level,heater radiator(core), etc. Mine heats things up fast. Haven't had any problems yet (knock on wood), except that the console lights around A/C levers tend to dim/flash when I slide A/C climate control levers from cool to warm and back. Hope this helps.

Again: thanks man !


..Does the heater-system have an air-filter somewhere ? I can't see such a thing in my Haynes
but IF it has; the symptoms are very much like a semi-clogged filter

..Does the system have a central 'port' ( for lack of better term. English is not my language )
to shut off the air-intake ( into the heater system ) ... that might be stuck in this case ?

..That manual you so kindly put up images from .. what manual is that ?
Is it this one ?
manual.jpg

[tbkilb01]

No cabin filter to clog. Yep, thats the same book. You have it?
Could you make out the pics? Just search 'heater core' in search feature and theres Tim giving all kinds if good suggestions,direction,answers..

[TheMAN]

So, when changing the blower speed setting, you can feel the air flow change? Setting the switch to "HI" gets you a lot of air, just not warm?

[octane98]

"..no cabin filter to clog..."
OK

"..Yep, thats the same book. You have it? .."
Nope, but I'll order it

"..Could you make out the pics?.."
Yep. Thanks !

"..Just search 'heater core' in search feature and theres Tim giving all kinds if good suggestions,direction,answers.."
Mmmmm ... I must be dim cause I can not seam to find those post

[octane98]

So, when changing the blower speed setting, you can feel the air flow change?

Yep

Setting the switch to "HI" gets you a lot of air, just not warm?

Nope.
As I wrote in my first post:
I'm getting VERY little hot air into the cabin.
The temperature of the air is just fine ( as in hot )
but I just get VERY little of it no matter what I do.

[celeron55]

In mine, the issue was that the blower fan was turning in the wrong direction. The airflow in that case is very minimal and the wire colors suggest that it should installed that way, but actually it's the wrong way.

The fan has a red and a black wire, and they must connect to a black and a blue wire respectively and it must be turning counter-clockwise, if I recall correctly. That's how it gives the most flow so it must be correct.

[octane98]

Thank you 'celeron' !

..I'll check that and report back.

[TheMAN]

Yep


Nope.
As I wrote in my first post:
I'm getting VERY little hot air into the cabin.
The temperature of the air is just fine ( as in hot )
but I just get VERY little of it no matter what I do.

so in other words, switching to "HI" does not give you high speed air (wind)?

[octane98]

so in other words, switching to "HI" does not give you high speed air (wind)?

That's right. I crank up the setting to HI
and the blower goes up in speed, and sounds like any other vent-blower in any other car going full-speed
... and there's still VERY little air-flow coming out any of the vents

[tbkilb01]

That's right. I crank up the setting to HI
and the blower goes up in speed, and sounds like any other vent-blower in any other car going full-speed
... and there's still VERY little air-flow coming out any of the vents

Heres a pic of the damper positions. Maybe somethings been fiddled with by PO. Air should be blowing really hard out off the center vents when the fan is on set to high! Cold or hot! Even while on low the heat is really a bit much to bear. Its the same temp as your motor. And the A/c blows cold too!
Did you ever check the A/c control cables adjustments? I sent you a pic the first time. I can resend if too blurry. Not a problem.
I dont know why pic keeps showing sideways

[TheMAN]

I suspect the blower motor is running in reverse due to improperly connected wires, like celeron said
It's so easy to do this when you install an aftermarket blower motor because it just comes with bare wires, no connector.... I had to cut off the connector from my original motor and solder it to the new motor, paying attention to the polarity, of course

[MaxiMoose]

Greetings fellow previa nuts!

I've been lurking these forums a good while but finally came out of hiding to chat.

So I'm having a weird issue with my 94 alltrac S/c. In the winter when I hit the heat it brings warm air, not hot but warm enough to live with. That kind of sucks a little but it's not my DD so meh.

The weird issue is only cold air comes out of the floor vents. Like no matter what I do the floor air is cold. It's warm at any other vents and even when it's on dash/floor mix the dash is warm the floor is cold. How is that even possible? Air is either going through the heater core or it's not right? It also doesn't matter if it's on outside air or recirculate and even if that was an issue it SHOULD make the blend of warm and cold cover the whole air system in effect making all the vents lukewarm. It's almost like the floor vents are bypassing the heater core but they shouldn't be able to unless that heater box is built really REALLY weirdly. I can't find an internal schematic or pics of one apart to see. Short of hitting a junkyard and ripping one apart I'm just guessing. I have already replaced the core because it was leaking when I got the van and I followed Tims method (That was a godsend btw Tim, thank you sir!)

What do you guys think? This is my second alltrac S/C prev. My last one was a 95 and it had hellfire and brimstone under the dash. Hottest heater I've ever experienced in a vehicle and I loved it. I used to deliver newspapers with it and even in sub zero weather I had both windows down and was in only a t shirt and I would be sweating. It was a monster. I hate that this one isn't like that because I'm not at all into cold.

I've been pretty deep in these vans having done a supercharger swap and a motor swap before but this heater thing perplexes me. I sure don't wanna rip apart the whole dash but I fear I may have to.

I know that was a good amount to digest but I like to be thorough and show my work.

Thanks in advance for any ideas!

[Jonny]

Your warm-not-hot issue might be a malfunctioning air mix damper. Mine is the opposite... it blows warm when the dashboard setting is on cold.
Edit. Just realized the hot/cold valve under the hood for the heater core is a more likely culprit. Just checked mine. When the dash lever is on hot the lever on the valve is at about 8 o'clock, and when on cold is at about 10 o'clock (when looking into the hood from the front of the vehicle). On mine just now I noticed that when the dashboard lever is on cold I could still push the valve lever with my finger about 15 deg further towards the cold/closed position, so this is the probable explanation for my warm air problem. Maybe your van never gets blowing really hot because the dashboard heat control doesn't move the valve far enough to the open position?

I wonder if cold air could get to the footwells if the footwell duct has a junction which has come apart? Combined with your warm-not-hot problem this might be responsible for cold air at that one place. Just a guess. Doesn't seem too likely but you never know.

Do you recall whether any of these symptoms were there before the heater core replacement?

[Previologist]

I suspect the blower motor is running in reverse due to improperly connected wires, like celeron said
It's so easy to do this when you install an aftermarket blower motor because it just comes with bare wires, no connector.... I had to cut off the connector from my original motor and solder it to the new motor, paying attention to the polarity, of course

I suspect this is happening to me now. I didn't mark the wires when I disconnected my direct-wired blower after the accident. It blows fine but nothing comes out. I figured I had a 50% chance of getting it right but I apparently still managed to get it 100% wrong.

EDIT: Yep, that was it.

[Dougseabird]

I’ve got the same cold-air-on-feet problem in my 1991 Previa that I just bought in Washington and drove home to Alaska. Heater works fine otherwise but no warm air to feet. AC doesn’t work but that’s not a problem in Alaska. Cold feet are! Cold air amount depends on drive speed, not fan setting, so there’s a leak to the outside somewhere and a damper not getting warm air to the floor vents. Any advice before I take the dash of my “new” van apart?