On cold days, the heater in our '90 SE blows cold for what seems like a very long time. If the drive is long enough, it does eventually start blowing warm. But it takes much, much longer than our other cars and any other car I can remember?

Any suggestions on what the problem might be?

 

there's a little up down lever to the side of the heat/ac controls. is it flipped down?

 

Like DanNY mentioned it would be a good idea to check to see if the fresh air vent is open. If the little lever is up its open and down its closed. Also you may possibly have a bad thermostat which isnt too difficult to change and is pretty inexpensive. If its the vg engine there is also a small 8mm bleeder screw on top right side of the upper intake manifold that you could open to bleed out any possible air bubbles that might cause an air lock in the system.

 

If I remember correctly, the bleeder screw didn't appear until either 1992 or 1993.

But another thing to check would be the water shutoff valve for the heater core. The vacuum line to it will fall off and then the valve won't respond to the temperature control lever.

 

My 1990 SE definitely has a bleeder screw.

I liked the suggestion about the cut off valve, it's easily missed and can definitely be an issue. Alternatively, if the tstat is good, and you don't have any air in the system, you may need to replace your heater core - it may be clogged. Mine behaves the same way, it's very much chock full of rust, even after flushing repeatedly.

I hope for your sake, it's not a heater core. Such a chore to replace.

 

Yep, I practice it much on junkyard cars and I have still yet to remove one.

 

I seen that fresh vent lever sometimes breaks from the wire rod it pushes and pulls but im not sure if it would fail open or closed or wherever position it was last in
you should hear a quiet flap noise when you open and close it and feel some resitance

when i got my 91 soo long ago,at first the coolant temp wouldnt warm up\low heater air etc.
so i did the thermostat (it can be ninja'd in without removing as much as the books say...true story)
the old stat in there was a fail safe with the rubber seal and it was crumbled away.

 

If you hear a gurgling coming from the dash, your heater core is partially clogged w/ crud. I pity the fool who has to replace one, as I too am such a fool. But damn, do I get HOT air now!!
So if it's just a stat or cut-off valve, do yourself a favor and power flush the system and replace w/ new coolant and DISTILLED WATER, not tap water. That will eliminate the minerals in tap water from precipitating out and caking up in your system.

 

If it is the heater core, search my heater core adventure here in the 3rd gen forum. I saved probably $1000 by doing it myself. That's like half the value of car itself!!