NOTE: The following was written for a 1989 model. Check to see if these instructions apply to your model before proceeding.

Replacing the heater core is relatively easy on the Reatta. I read the manual when the core let go on my '89 the first time. I postponed the job until the following winter before tackling the job. I have had to remove entire dash boards in the past for core R&R. The Reatta does not require such extensive surgery.

1. Start by removing the glove box, you'll need a short handle torx driver to remove the screws.
   
   
2. Remove the bottom cover under the dash, you'll need a 7mm nut driver and 10mm socket and extension for the lower retainer nuts on the firewall.
   
   
3. On the far right of the dash is the ECM and Climate Control Module. (this is the hardest part of the job). Remove the 7mm screws holding the CCM in place (there are 3 I think) and carefully remove the control rod from the top of the CCM. (looks like a long threaded rod). Carefully slide the CCM down and out of the dash. *Don't forget to disconnest the wiring harness.
   
   
4. There are two 7mm screws that secure the ECM in its mount, remove them and disconnect all wiring connectors to ECM and slide down and out.

   Make sure the battery is disconnected before removing any wiring harnesses.

5. Next, there is another module on top of the heater core compartment, remove the two 7mm, screws and slide it out through the glove box opening.
   
   
6. There are two 7mm screws holding the heater core cover to the assembly Remove them and pull the cover away from the firewall and out from under the dash. A little patience goes along way while doing this as it is a rather tight fit. The heater core is now fully exposed and assuming you have already removed the heater hoses, is almost ready to remove.
   
   
7. There are two 7mm screws holding the core in place, remove them and slide the core out.

Installation is the reverse of removal.

Use a lubricant on the heater hoses to install on the core.

I would suggest performing a pressure check on the cooling system to check for leaks before reassembling the heater core compartment cover and related items. If I had done this with the first core, I would not have had to do the job twice. Turns out there was a weak solder joint on the heater core that let go a month after installation.

Re-installing the compartment cover is a little tricky, just make sure it is properly seated in its proper position.

The whole job took me about an hour and a half to complete. I believe I have covered the process completely, but if you run into any problems, feel free to drop me a line.