Steve Baur
Former Editor, Modified Mustangs & Fords
December 1, 2009

Last month we tore into our resident '90 Mustang coupe and gutted the interior space to make way for a host of new components from Latemodel Restoration Supply and Corbeau. To provide a solid foundation to build on, we called Thermo-Tec for some of its sound and heat insulation material and proceeded to dampen the resonant characteristics of the Mustang's unibody chassis. This month we move ahead with this comprehensive interior restoration by prepping and painting all of the interior pieces, and then tackle the heater core and door-lock actuator installations.

Changing the heater core in your Fox Mustang is probably the worst mechanical job that you can perform on the car. It's long, tedious, and the chance of breaking the various plastic tabs, fasteners, and wiring harness plugs that are all intertwined within the dash is extremely high. But not having heat in your car sucks, and cold, muggy days will require you to keep a rag on hand to handle the defroster duties. If you happen to have a non-air conditioning car, the job is actually much easier, but I think the majority of 5.0L owners have to do it the hard way, and that's what we had to do.

We covered the dash removal last month; this month all we had to do was disconnect the A/C lines from the evaporator, and pull out the HVAC box that is bolted to the firewall. If you have to perform this job, pony up for a new A/C evaporator and do both at the same time. Failing heater cores have a tendency to fill up the bottom of the black box with coolant and erode the evaporator at the bottom. Pulling the dash is already a tedious and risky job, so make sure you only have to do it once.

We had just installed a new heater core and A/C evaporator last year, but we evidently bumped the heater core tubes a little too much during this year's engine changes-upon removing it, we found that the solder joint that welds the tube to the core had broken free. The leak was catastrophic, so we didn't give it time to saturate the evaporator in the case by leaving it connected. The engine probably would have run out of coolant in a short amount of time if we did. Latemodel provided us with a new heater core (PN LRS-18476A).

With that problem fixed, we moved to the new door-lock actuators. When we bought the coupe, the actuators were locked in one position, and we had to pull them out just so we could lock the car. Failing actuators are a common problem on older Fox Mustangs, so it's really no surprise, especially considering all of the other things that have been wrong with the car from the outset.

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