Pulling heater box

[coolwind57]

So I'm going to go ahead and pull my heater box for the first time, probably next weekend.  My heater core is clogged and puts out nearly zero heat, even after multiple flushes.  BTW, I've got the original R12 AC system.  

 

Is it a possibility that I won't have to disconnect the evaporator core or otherwise compromise my AC system in order to pull the box, replace heater core and reseal the box?  Never been in there, so asking those who have the experience.

 

 

[Limeyjeeper]

Not really. The evaporator is in the heater box which is held together with screws. Also the evaporator itself is probably held in with some screws. It might be possible if you pull the dash.

[coolwind57]

8 minutes ago, Limeyjeeper said:

Not really. The evaporator is in the heater box which is held together with screws. Also the evaporator itself is probably held in with some screws. It might be possible if you pull the dash.

Was fully expecting to pull the dash.  Really need to know for sure if I can accomplish my mission of replacing heater core and resealing box without compromising evap core or AC unit.

[Dzimm]

I know the newer ones require it to be fully removed to open it up.  I'm sure the old one will be the same way unfortunately.  It sits somewhat recessed into the firewall so it would be impossible to get to any screws that may be on the backside of the box.

 

When I flushed my clogged core I had to shove my garden hose into a rubber hose and duct tape the seam up so no water could leak, then cranked the hose wide open.  Required the full force of the hose before the clog came out.  Make sure to flush it backwards first then forwards.  May need to give that a try before tearing into it, worst case it blows a hole in the heater core so you'd be replacing anyway.  

[scaleless]

You can absolutely open the heater core side without removing the AC lines, but it will be very tight.  You can even pull the evaporator without disconnecting it, if you wanted to for some reason.  As for the logistics of getting the screws out with such tight clearance?  Well, don't ask me.  It doesn't hurt to pull the dash first, loosen up the AC components to get some slack, and see how far you can get into opening the box before disconnecting the AC lines if you have to.

 

 

All the screws are on the top.  If you can get the box angled towards you 45 degrees, it should be trivial.  There are two screws retaining the core.  See this image for reference:

[Limeyjeeper]

Here are some more images. The expansion block will make it extremely difficult to get enough play. The AC Evaporator is usually screwed into the heater body and there might be a thermostat wire in the core depending on the year.

 

 

 

 

 

 

 

[coolwind57]

Can't thank you enough for all the pics and direction.

[coolwind57]

Update:  Well got it all back together and running now.  I pulled Evap Core, and did a complete delete of my AC system.  I really didn't use it much even when it did blow cold air and I really like the simplicity of working on my engine now anyway.  Tons of room now.

 

Blowing HUGE heat now, but I have lost ability to toggle between cabin zones--it's just blowing up the defrost vents.  I checked my vacuum hose running out the firewall into the vacuum ball.  I've got vacuum there.  I checked for vacuum inside the cab at the controller.  There's the group of vacuum lines that forms into a single rubbery port that plugs in the back of the controller.  I'm not detecting vacuum there.  Shouldn't I?

 

I was quite sure I had plugged everything back in as I reinstalled the box into the cab.  Yet its still pushing air to the default defrost vents.  Does this jump out to anyone?  I checked the individual ports that's neares the gas pedal.  They're plugged in they're appropriate diaphram.  I manually (mechanically) moved the diverters by hand and air does move, but I have zero input from the controller itself.  

 

Any particular thing I'm overlooking that I need to check with this symptom?  

[eaglescout526]

It’s possible that the hard line from the vac ball to the controller got hard and broke in a spot where you won’t know that it broke. I mean it is 30 year old vacuum line after all. 

[Chad R]

I have a question I’m going to be pulling heater box replacing heater core, but my vacuum line going to heater box has fallen apart.  What is the best replacement for that line rubber line plastic line or something else

[eaglescout526]

1 minute ago, Chad R said:

I have a question I’m going to be pulling heater box replacing heater core, but my vacuum line going to heater box has fallen apart.  What is the best replacement for that line rubber line plastic line or something else

I’ve gotten rubber line that slips over the old lines. Never had a problem. 

[Chad R]

12 minutes ago, eaglescout526 said:

I’ve gotten rubber line that slips over the old lines. Never had a problem. 

Ok thanks I will use that.

[scaleless]

If it's just a small break or nick, electrical heat shrink tubing works great for that

[Chad R]

23 minutes ago, scaleless said:

If it's just a small break or nick, electrical heat shrink tubing works great for that

No mine is falling apart you touch it it breaks

[jdog]

possible that you pinched a line going back together?

[cruiser54]

[coolwind57]

28 minutes ago, cruiser54 said:

Done that already, Cruiser.  Very happy with the results.  Highly recommended.

 

Good Lord, I hate the thought of pulling my dash again to trace those vac lines.  Sounds like that's in order it seems.  Was hoping for a simpler troubleshooting strategy.  

 

 

[cruiser54]

Tracing can be done by getting access to the heater contol. You could run a new vac hose if needed.