What would cause a 1989 Toyota Supra heater to blow only cold air?

Answer 1

Your heater core is bad and needs to be replaced. It's a pain. Here is how you replace it. Remove Center Console Cover 1. Remove screw on side, below back driver's corner of center console. 2. Remove ashtray. 3. Remove 4 screws behind ashtray. 4. Pull up on back (behind shifter) of center console to unsnap. 5. Continue pulling to unsnap three spots around heater control area. 6. Undo connectors. 7. Remove console cover. Remove Heater Control 1. Remove 3 screws on heater control. 2. Undo connectors. 3. Remove heater control. Remove Stereo 1. Ensure 4 screws at corners of stereo opening are removed. 2. Remove your stereo. Remove Center Console 1. Remove screw on bottom of armrest pocket, near front. 2. Remove carpet in bottom of center pocket between shifter and lumbar/mirror switches. 3. Remove screw at bottom of center pocket. 4. Remove 2 screws on sides of the center console near the back. 5. Remove 2 screws on front, top of console in front of shifter. 6. Undo connectors. 7. Remove center console. 8. Undo connector going to handbrake. 9. Undo 10mm ground bolt underneath the carpet strip running behind the shifter. 10. Route wires out from under carpet strip. Ensure they are loose from any bindings. Remove/Loosen Shifter 1. Manual: Remove 4 10mm bolts/screws holding rubber boot. 2. Remove boot. 3. Untuck rubber seal from around shifter base. 4. Remove 4 10mm bolts/screws around shifter base. 5. Remove shifter 1. Automatic: Remove 4 10mm bolts. 2. Undo connectors. 3. Slide/Tilt the shifter as far back as possible. Remove Driver's Underdash Cover 1. Remove 3 screws at bottom left and right side corners. 2. Remove screw underneath left switch cluster (cruise, driver's lights, etc). 3. Remove 2 screws under the hood latch release. 4. Pull hood latch release through the cover. 5. Unhook floor light. 6. Push down on back to undo the spring clamp around the steering column. 7. Remove cover. Remove Driver's Underdash Duct 1. Pull down to remove duct. Remover Left Switch Cluster 1. Pull out to unsnap cluster. 2. Undo connectors. 3. Remove cluster. Remove Gauge Cluster 1. Remove 2 screws at bottom corners of cluster cover. 2. Remove 5 screws spaced across front underside of cover. 3. Remove cover. 4. Remove 3 screws across top of cluster. 5. Undo connectors. 6. Remove cluster. Remove Driver's Kick Panel 1. Remove 4 screws along strip. 2. Remove strip. 3. Remove 2 screws on dead pedal. 4. Remove dead pedal. 5. Remove 10mm nut at front of kick panel. 6. Remove kick panel. Lower Steering Column 1. Remove 2 17mm nuts at either side of steering column (notice ground loop on right side one). Remove Glove Box and Covers 1. Remove 3 screws along front of passenger's underdash cover. 2. Remove underdash cover. 3. Remove 2 hinge screws at botton of glove box. 4. Unlatch glove box. 5. Remove glove box. 6. Remove 2 screws at top corners of glove box undercover. 7. Remove 2 screws at glove box latch. 8. Remove latch. 9. Loosen plastic hold down screw in center back of undercover. 10. Remove glove box undercover. Remove Passengers Kick Panel 1. Remove 4 screws along strip. 2. Remove strip. 3. Remove 10mm nut at front of kick panel. 4. Remove kick panel. Remove ECU 1. Remove 2 screws. 2. Undo connectors. 3. Remove computer. Remove HAC (on glove box hinge bar, if equipped) 1. Not sure how. The car I did the write up on didn't have one. If you do this, email the procedure to me and I will include it. Remove Anti-Slip Computer (if equipped) 1. Remove 2 screws. 2. Undo connectors. 3. Remove computer. Remove Dash Pad 1. Remove 10mm bolt/screw at bottom left corner of dash pad. 2. Undo big, green, rectangular connector by driver's fuse block. 3. Undo medium, blue, rectangular connector by driver's fuse block. 4. Undo medium, white, rectangular connector by driver's fuse block. 5. Undo big, square connector that attaches to driver's fuse block. 6. Unclip the speedometer cable connector. 7. Move speedometer cable connector out of hole. 8. Remove 2 10mm nuts on either side of speedometer cable connector. 9. Remove 10mm nut deep inside dash directly above the right nut in step 5. 10. Remove 10mm nut deep inside dash above and to the left of left nut in step 5. 11. Undo big, square, white connector to right of nut in step 7. 12. Remove 2 screws around heater control area. 13. Remove 10mm bolt/screw at bottom right of dash pad. 14. Remove 10mm nut above area ECU area. 15. Undo small connector to interior temp sensor above ECU area. 16. Undo medium, yellow, rectangular connector by where the wiring harness runs through the firewall. 17. Pull out on the dash pad about 2-3 inches. 18. Remove dash pad by tilting up and over the steering wheel and shifter. Remove Cross Bar 1. Remove 2 12mm bolts on left side of bar. 2. Remove 2 12mm nuts on left side of bar. 3. Remove 2 12mm bolts above the steering column. 4. Undo wiring harness clip behind bar above the steering column. 5. Remove brake pedal spring. 6. Undo 2 wiring harness clips from left of center arm. 7. Remove 2 12mm nuts at the top of the left of center arm (notice ground loop). 8. Remove the 2 12mm bolts at the bottom of the left of center arm. 9. Remove the arm. 10. Undo the wiring harness clip from the right of center arm. 11. Remove 1 nut 12mm nut at top of right of center arm. 12. Remove 1 12mm bolt at bottom of right of center arm. 13. Remove right of center arm. 14. Undo the wiring harness clip above firewall pass through. 15. Remove 3 12mm nuts on at right of cross bar attaching it to the bracket (not the 3 holding the bracket to the car). 16. Pull out on right side of cross bar. 17. Pull bar out the passenger door. Remove Heater Core Box 1. Undo heater hose under hood by heater VSV. 2. Undo heater hose under hood by the brake booster. 3. Undo 3 connectors on left of heater box. 4. Unclip floor heater ducts. 5. Remove 4 10mm nuts at the corners of the heater box. 6. Remove 2 10mm bolts/screws holding the heater box to the a/c box. 7. Remove 2 10mm nuts on top of a/c box. 8. Remove 10mm nut on bottom center of a/c box (may be under carpet). 9. Loosen heater box by pulling out on left side first (pull on opening directly on top of the heater box not the ones on the sloped part or the left side as this can break off the plastic tabs). 10. Remove heater box. Remove Heater Core 1. Remove 4 screws and clamps on top of heater box. 2. Remove the heater core.