300ZX (Z31) Forums Dedicated to 84-89 ZCars otherwize known as the Z31's

Heater core

Old 11-30-2002, 11:05 PM
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Join Date: Oct 2002
Location: Oregon
Posts: 8
Re: Heater core

Don't know if anyone answered you, but I just replaced the heater core in my 84 na. It is a major job and took three evenings to get it out and another three to put it back in. I got quotes from parts houses that ranged from $84 to $104. I finally decided to to take the core to a local radiator repair shop to see if it could be repaired. The bad news was that the unit was DOA, but the good news was they ordered a heater core for $70. I found the following post on the Z31 website to be very helpful. The part about bagging and labeling, and making notes is critical when doing the reassembly.


Subject: More AC fixes

This might be archive material-

Replacement of defective vacuum motors in the climate control system.

This was done on an 85 N/A with automatic climate control and digital dash. I have had problems with the A/C just about as long as I have owned the car. It never put out enough airflow to cool the car. Over time, I have replaced every piece of vacuum hose in the system. This did not correct the problems. Finally, I traced the problem to two vacuum motors that operate air mix doors one and two as per the diagrams in the service manual.

To troubleshoot, I applied vacuum directly to the devices and found that neither held vacuum pressure. So, to get the A/C working again, it was necessary to replace both of them. This meant complete removal of the dash to remove the heater box, since both devices are mounted on the rear of the unit next to the firewall where they are simply impossible to access otherwise. I will go through the procedure in steps, with notes as needed. Allow a weekend to do this, and have needed parts in hand before starting. Above all, be careful. You will encounter brittle plastic pieces, which will break without much provocation, and be careful of wiring. Wires will become brittle with age as well.

Air ratchet (not necessary but a real timesaver)
Metric socket set w/extensions and metric wrench set
Metric swivel sockets
Long shank #2 philips screwdriver
Needle nose pliers
Needle nose pliers with angled jaws
Regular screwdrivers-various sizes
Last but not least- patience

PART NUMBERS for vacuum motors:
I highly recommend getting new heater hoses as well.

Here are the steps I used in doing this repair:

1. Remove kick panels from driver and passenger side Ė 3 screws driver side, 2 on passenger side.
2. Disconnect car battery.
3. Remove courtesy lamps from the kick panels; remove the bulbs from the harness and set them aside.
4. Remove Glove box. 4 philips screws, 2-10mm bolts. You will have to get the glovebox out of two wire loops that limit its travel to remove the Philips screws. Unhook wiring for glove box light/switch. Set glovebox aside, keep the screws/bolts in it.
5. Remove ashtray and then remove bezel for radio/climate control, 2-10mm bolts, 2 philips screws. Unhook wiring for cigarette lighter, set bezel aside, and keep the screws with it.
6. Remove radio/climate control assembly. 4-10mm bolts. Carefully unhook all wiring harnesses.
7. Remove Compass/MPG/G-force meter. 2 philips screws in the top of the radio/climate control opening. Unhook harness, set unit aside with the screws.
8. Remove two switch clusters on both sides of digital dash. Use 10mm swivel socket with extension to remove two nuts from the rear of the switches. You will have to get down on the floorboard to see under the dash to loosen them. Gently pull out switches and disconnect them from the wiring harness. Put the nuts back on the switches and set aside.
9. Remove steering wheel; first remove horn cover, then remove upper and lower trim pieces that cover the steering column. 4 philips screws.
10. Locate the wiring harness that comes from the steering wheel switches control box attached to the steering wheel. Follow it to the steering column and disconnect it from the harness. Disentangle it so it is hanging loose.
11. With a breaker bar and a 19mm socket, remove the nut that secures the steering wheel to the column.
12. Either use a steering wheel puller, or (in my case) jiggle the steering wheel until it comes loose. Then remove it from the column. Place nut and washer back on steering column temporarily.
13. Remove two Philips screws from the top of the digital dash trim cover.
14. Remove two Philips screws from the sides of the digital dash unit. Carefully remove the trim piece. Youíll have to jiggle it some to work it out of the opening.
15. At this point get some masking tape and some old newspaper. Use the paper and masking tape to cover the surface of the digital dash as best you can to try and prevent scratches.
16. Unplug 3 wiring connectors in the top of the dash opening. Locate the wire harness on the rear of the digital dash unit; follow it to the power supply and unplug it. (2 connectors)
17. Remove the digital dash unit from the opening. This is a very tight fit, take your time, and donít break anything. Be sure to keep an eye on the trip odometer buttons so they do not get broken. I stress again, take your time here. Set digital dash aside.
18. Remove two Philips screws from the three harness connectors in the top of the cavity. Then remove two more screws to loosen the harness from the top of the dash cavity.
19. With the wiring harness loose from the top of the dash, you will be able to easily remove the driver side defroster vent. Push on the plastic clips that hold the vent in position, and push it up out of the dash. It should come out easily.
20. On the passenger side, get a screwdriver and gently push it under the corner of the defroster vent. Holding it there, use another screwdriver to push the retainer clip forward, which will release the corner of the vent. As I remember, there are a total of four of these clips. Start at the passenger side, and work your way towards the drivers side, releasing the clips and removing the defroster vent. The vent will suddenly pop out of the opening, be very careful of the optical sensor in the vent. Carefully pull the wiring on the sensor until two connectors emerge from the dash. Carefully disconnect the two plugs. There is a little square button you will have to squeeze down to get the plugs apart. They are brittle, I broke one trying to get it apart. Be careful with this- you do not want to damage the sensor or pull the wires out of it.
21. Now that the defroster vents are removed, you will see a total of four 10mm bolts down in the vents. One in the driver side vent, 3 in the passenger side vent. I used a small 10mm socket on a ratchet to remove all four. Mark screws and set them aside.
22. In the radio/climate control opening, you will see two 10mm bolts on each side of the opening. Remove them, and set aside.
23. Under the dash in each corner, locate and remove one 10mm bolt from each side that secures the dash to the framework underneath.
24. Loosen the collar that secures the turn signal/wiper switch unit to the steering column. This needs to be loose so it can be rotated.
25. On each side of the dash, locate and unplug the wiring harnesses from the connectors on each side kick panel. There are 3 connectors to be removed on each side.
26. Get someone to help you, and begin lifting the dash to get it out. This is awkward, and is much easier with two people. Be careful, donít bend the metal edge where the dash meets the windshield glass. Be careful of wiring harnesses getting caught on things when you remove it. You will have to wiggle the turn signal switch to get the dash past it. Watch scraping your gearshift **** with the lower metal edges of the dash. Set the dash aside in a safe place.
27. Carefully remove the ductwork. Numerous screws and wiring harnesses to disconnect. Canít remember all the details on the screws, but bag them and label where they came from. Pay close attention to how the ductwork is routed, and make notes as you go.
28. Remove the digital dash power supply- one 10mm nut, one 10mm bolt. Set aside, keep bolt and nut with unit.
29. Begin removal of metal framework. 3 bolts on each end, 2 nuts on each side of radio cavity. Remove two bolts that secure steering column to framework. Remove bolts securing hood release cable. Then, you will have to pull the steering column out of the way to remove two more bolts that secure framework. There are two bolts on each side of the metal that forms the radio cavity that need to come out. Pull the carpet back and remove them. Remove and set aside the metal plates. You should now be able to remove the metal framework from the car.
30. Next, you will need to disconnect the heater hoses under the hood. It is necessary to remove the water control valve to get to the heater core connections. Remove ďSĒ shaped hose coming from the top of the valve from a water line coming from the block. I ended up cutting the hose coming off the bottom of the valve, because I could not get it to come loose. Unplug wiring harness and vacuum hose from the valve. Remove valve. Be very careful with the wiring going to the valve. Mine was very brittle, and I broke one of them. I had to repair the wiring. Disconnect the second heater core hose. Both heater core inlet pipes should be bared now.
31. Disconnect vacuum line coming from passenger side of the dash that goes to the bank of solenoids.
32. Remove two 10mm bolts securing the heater box to the console, in the front on the hump.
33. On the bottom rear of the heater box, remove two Philips screws from the mounting tabs, where it is secured to the firewall.
34. Remove the 10mm bolt securing the A/C evaporator unit to the dash, then remove the Philips screws on the bottom tab of the evaporator. This needs to be loosened so you can move it about Ĺ inch to the right.
35. Remove metal band that seals opening between the evaporator unit and the heater box. One 10mm bolt.
36. Unhook wiring harness that goes to the bank of solenoids.
37. Very carefully remove the heater box from the dash. You will need to gently push the evaporator unit to the right a little to get the heater box out. It should come out without too much difficulty.
38. Now, the whole purpose of all of this: replace the two vacuum motors. Make sure all the levers on the actuators get put in the right place. It would be highly advisable to replace every piece of vacuum hose that you see at this point, while they are easy to get to. After replacing the motors, apply vacuum to them and be sure that the actuators and the doors they operate are working smoothly. I, for one, would not want to do this again anytime soon. If needed, the heater core itself is easily replaced at this point as well.

Reassembly is basically the reverse of this. Allow yourself plenty of time to do this, and in retrospect, I would recommend just getting new heater hoses and cutting the old ones to get the water control valve out. It would have been easier that way. Now that this is done, the A/C works great. It was a long job, but it was worth it to get the A/C working right. Sorry for the lack of pictures, but I do not have a decent camera. I hope this will help someone down the road, either in fixing the same problem I had, or in changing the heater core. Iím not really a mechanic, but I got this accomplished and everything works right. Donít be afraid to tackle it, just allow plenty of time. Make notes as you are disassembling things, they will be helpful when putting it all back together. If you need to do this, feel free to e-mail me with any questions. I also have a service manual for a 1985 Z that I could e-mail scans of if needed.

-Bob H 85 N/A

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Old 12-12-2002, 08:00 AM
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Join Date: Dec 2000
Location: Houston, Tx
Posts: 342
Re: Heater core

That procedure is quite helpful, but has a LOT of unnecessary steps in it. To pull the dash, you do NOT need to remove the instrument cluster NOR the center gauges. You can also leave the glove box alone. Best to leave them in where it will not get damaged. The connectors going to the sunload sensor (in the center of the long dash vent - only on auto climate control cars) are often brittle and break trying to disconnect them. I advise to leave them connected, but push vent out of the way while you unbolt the 3 10 mm bolts that hold the dash in under that vent.

To pull the dashboard, you only have to remove all the trim panels below the dash and around steering column, the steering wheel, the steering stalk switches, the radio/climate control unit and surrounding trim, the lower kickpanels and the defrost vents on the top of the dash (so you can access the bolts to unbolt the dash. Once all this is removed, merely unplug the harness from either end (near ecu, and similar connector contraption in same vicinity on drivers side), the speedo cable (only on analog cars from 84-6). The whole dash can come out as a unit, with everything still in it (clusters, gauges, vents, glovebox, etc).

Then you can also remove the large metal brace going the width of the car to make things even easier.

Now the heater core can be easily accessed.

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Old 06-27-2016, 10:30 AM
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Join Date: Jul 2013
Posts: 34
Many Thanks!!.... also have an '87 Z31 Heater core rupture, just the information needed to avoid unnecessary steps!

....posted 08.10.2016.....WELL!......THREW THE FACTORY MANUAL AWAY.....Folks...JUST LOOK!.....the hoses tell the story....AND the vacuum unit!

Last edited by Virtuoso; 08-10-2016 at 02:13 PM.
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Old 07-10-2016, 09:02 AM
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Join Date: Jul 2013
Posts: 34
Got the same problem, am looking to bypass it since Winter didn't happen here last year.
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Old 08-10-2016, 02:15 PM
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Smile Z31 Heater Core Rupture....

LOOK...it's right there in front of you!!
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Old 08-10-2016, 02:29 PM
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Unnecessary...other than Northern Climes
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Old 08-10-2016, 02:31 PM
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Posts: 34
Z31 Heater Core

All for naught in TEXAS....don't need it, not gonna pay for it, the parts / time / labor spent IS UNNECESSARY HERE....
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Old 08-10-2016, 02:32 PM
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Have video pilgrims~!~
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