1997 Tran Sport Montana poor heat

[eleveniron]

I have very little air flow from the ventilation system when I am in HEAT mode. When in COOL mode I have tons of air flow.

I've been able to just barely get the cover off of the bottom of the heater core and confirmed that there is plenty of airflow through the core, so it is not plugged. But when I put the cover back in place you can hear the fan cavitating from the back pressure.

The motor that changes the flow to the heater core or to bypass the heater core is working. I'm getting full hot and full cold, but just very poor flow when I select heat.

I'm just wondering if there is possibly two valves that this motor has to move, and is it possibly only changing the valve that controls the air into the core?

It is next to impossible to get at the insides of the ducting and the valves. Any help would be appreciated!

Thanks!

[LMP]

Just one question to make the situation clear for all who would suggest a solution: do you talk of air flow through the SAME ports?...
HEAT and COOL: is that the mode buttons (heat to the floor, cool through the upper vents) or is that the temperature slider moved from cold to heat?

[eleveniron]

Regardless of the mode (floor, vent or defrost), the amount of air flow is greatly reduce if i select from COLD to HOT. Something is blocking the air after the heater core. What ever it is, does not affect the air that bypasses the heater core (COLD selected).

[70RSZ28]

I believe you have another door staying shut even though your control valve is working and that door seem to open, the are so many configurations/possibilities, like def/heat, def/vent, just def, just heat, just vent. I'm guessing (kinda) but I bet there is another door keeping the air back, one thing that wasn't mentioned....when you move the selector to change where you want the air to come from can you hear or feel movement in all modes? Hot and cold. I would run it hot try all modes making sure you hear movement at each stage, from the full defrost to full vents to full floor. Another thing I remember we used way back when I was a wrench head (loved it) for a living, I used a coat hangar (make sure it's perfectly straight as to not get caught up on something around a bend) and I made a little ball end on it with black tape and slowly ran it through the outlets to feel movement and maybe to open a door if we are lucky, and if you do happen to open one, keep doing it until you find the valve, linkage or switch that is connected to it. Bingo you've solved the mystery.

Good Luck

Doug

[eleveniron]

Thanks guys... good ideas.

All the modes (floor, vent, defrost, etc) work properly. The air flow is the same regardles. I'd say i have only 25% of the airflow that i should have in HEAT, compared to when i select COLD. Again, there is tons of air coming through the heater core when i take the bottom cover off, so i know without a doubt that the core is not plugged. It looks like new and no leaks at all...very clean. There has to be two doors used to direct the air through or around the heater core, and the second door must not be operating properly...I just can't get at the bloody thing. I need to find a schematic of the ducting and controls.

Well, back outside to look at it for a few more minutes, then i have to put it back together so the wife can have her van back.

Thanks!

[GregA]

Not sure if it will match exactly, but there are a couple of diagrams here:

http://www.autozone.com/servlet/UiBr...3d801be979.jsp

Hope it helps,

Greg A.

[eleveniron]

Thank Greg...that does help. It confirms that there is in fact two doors. The tempaerature valve and the slave valve. My guess is the slave valve is not moving properly. Now, just to get at the damn thing...

Thanks!
Steve

[willisaon]

Hello,

This sounds very much like my problem that has just started on my '97 Transport.

Any luck in freeing up one of the valves?

Thanks,
Steve W

PS. I have an added twist in that speeds 1 to 3 on my fan do not work as well. (4 & 5 sound OK but just very poor volume of air). I have read other posts referring to a low-speed relay but cannot seem to locate it. Not sure if the two symptons could be related???

[eleveniron]

Steve,

The other night I bought a one year subscribed to ALLDATA. Would you believe there is a GM service bulletin for 97 trans sports to fix a problem with poor heat and air flow...have to look into it more but sounds exactly like the culprit.

The low speed relay is actually a resistor assembly. I had to change mine last year...all i had was HIGH on the fan. To get at it drop the blower motor out (3 screws, the wire harness and the motor cooling hose). The resistor assembly is mounted in the botom of the duct immediately behind the fan and is held in with 2 screws (have fun getting the forward screw back in).

Steve

[willisaon]

Steve,

I found these posts regarding a TSB to resolve "A/C - Poor Heat at Low RPM When Cold". Not sure if it is the same TSB but it seems more related to poor heat and not air flow.

http://www.talkaboutautos.com/group/...ges/65117.html

http://www.automotiveforums.com/vbul...d.php?t=324572

I just checked out my wife's '02 Pontiac Grand Am and it has the same loss of air flow once the Heat control is turned all the way to hot. It seems to be at least a 50% reduction in flow. This leads me to believe it may be just the design of the system...

I've also removed the HEPA filters in the TranSport as they were clogged with leaves and dirt. I'll leave them out until the spring, as it does seem to help somewhat.

The blower resistor does seem to be at fault for the speed 1 to 3 failure. Just checked the voltages going into the connector and they are all OK.

Steve

[LMP]

Originally Posted by eleveniron

..... drop the blower motor out (3 screws, the wire harness and the motor cooling hose). The resistor assembly is mounted in the bottom of the duct ..

Question 1: I understand the blower motor is accessible from inside the car starting with the '97 ? Right?

Question 2: Do you have a button labelled "bi-level" in the '98 model? (it does not exist in the '90-96 model). THe "bi level" mode , when it exists, allows heated air to be directed to the floor while the upper vents are fed with cool air. The slave valve depicted is controlled by the mode buttons and according to the manual should be opened in the HEAT(floor) and DEF modes. THe SLAVE DOOR is precisely used to implement the BI-LEVEL function and when in closed position, it does restrict the air flow available from the heater core, and this would then be a logical explanation in your case. (not same as HI-LO mix function that directs air (cold or warm or in-between) simultaneously to the upper vents and to the floor.)

The mechanical drawings from the GM service manual I have do show the slave door, but this door does not exist in the electrical and vacuum solenoid set-up of same manual . It seems the manuals carry some drawings from a year mdel to the next while some changes are ignored .

MAke sure you report your findings and if possible, with photos...

[eleveniron]

I haven't had a chance to get back into it yet. Pretty cetain I'm going to find that the bulletin that specifically details this same problem will solve it somewhat.

There is no bi-level in my 97 trans sport...not sure about the 98.

Yes, in the 97 the blower motor is right above the front passenger's feet. A couple screws to remove the soft cover at the bottom and you can then easilly get to the blower.

I've also taken the cabin filter out for now as it was full of crap (hence the reason for it too, i guess). It looks like most of the stuff in there is coming from mice. I'm making a point of keeping the system on the recirculation mode when I'm parked for any length of time so the solenoid keeps the door closed for the outside air. Otherwise a friggin cat could almost fit through there.

As soon as i get a chance to get back into this I'll make sure to post more info. Is there a way to post photos on here?

Cheers,
Steve

[LMP]

Originally Posted by eleveniron

Is there a way to post photos on here?

Yes insert your photos using this
[ing]http://www.LINK TO YOUR PHOTO HERE[/ing]
where it should read img at beginning and at the end and not ing (had to do this because it would try to link to some nonexisting link and show a red X) like this

but your photos must be hosted somewhere on the web, like you can open a personnal website on geocities.com or other smilar facilities and transfer your photos there in the first place.ALso first size your photos properly, most simple is using Microsoft Photo Editor, so they are around 400 x 300 pixels or less.

[llerrad]

Where are the filters you pulled out would like to remove mine. I have the same green and silver van, had heater core replaced and thermo done heat is still poor we have had temps down to -30C and on a long trip it just dose not warm up well.

[eleveniron]

The post with the picture of the van wasn't my post. That is a pre-1997 trans sport.

The 1997 and later trans sports have the filter access inside the glove box. Open the glove box, pull out all your stuff, and you'll see an access cover at the front. Pull off the cover and then open the little door right behind it. Reach in and pull out your hair and feather ladened filters.

Good luck!

Steve