fordforlife0225

Hey guys, I'm mostly on the 4.6 section since I sold my 3.8 about 3 years ago but I'm in need of some help. My good buddy has a 3.8 now and his heat isn't working. His brother helped him flush out the heater core but he still isn't getting heat. Any and all suggestions would be much appreciated. It's holding its coolant level and the engine is coming up to temp no problem. What all can we check, fix? Would a new thermostat do anything

petrock

Is he not getting any air flowing through the vents? Can you hear the blower motor turning on at all speed ranges? If you change vent modes does the air flow change? Or is the air going through the vents the same temp as the outside air? Or is it colder? Or is it mildly warmer?

A new thermostat wouldn’t help because all that does is allow the coolant to flow through the system when it has warmed up enough. If the thermostat was bad and not opening up to allow coolant flow you would see other problems like overheating.

Check that the hoses in the engine bay going to the heater core are warm/hot after getting the car up to operating temp. If not, and the other coolant lines are warm/hot, then there may be a blockage in the coolant lines somewhere not letting the coolant flow to the heater core. If the lines check out OK, then check if the A/C clutch is turning on when you have the heater on. The switch (or some wiring in the heater & A/C circuits may be crossed) may be bad and turning the A/C on when you select heat.

Good luck...

Stevo86

Kinda sounds like a vacuum line came off somewhere

LilRoush

I'd say it's a fan/vent issue instead of a coolant/heater core issue.

Make sure the vac lines are hooked up behind the HVAC panal and the 'heater' is really being selected when the dial is turned that way on the dash.

petrock

If the problem is that the vents don’t open/close according to the vent selector switch, then yes I would agree it is a vacuum issue since the vent doors are controlled via vacuum. A fairly thin & very brittle plastic hose coming from the vacuum tree by the brake booster going all the way across the engine bay and into the fire wall is the vacuum line for the vent doors.

However, if the vent doors open/close as expected then vacuum is not the problem.

fordforlife0225

i will get an answer to all those questions tomorrow morning. pulling off the center section of the dash, where all the a/c/heat ***** are will give me acess to the back of the panel that would show wether heat is being selected when the **** is turning that way? after that, check the line running from the brake booster into the dash?

fordforlife0225

Update:
Took a look at the car today.
-initially when you turn on the heat there is a few seconds of heat and then it goes to ambient temperature.
-all vent settings work. All fan levels blow. When you turn on the a/c the compressor clutches in and the vents blow cold, and the compressor does not short cycle.
-the lines going into and out of the firewall are 106degrees and 158degrees. The small line on the driver side is 106, the bigger line beside it is 158.


Few points of concern. There are some Home Depot components in the line. I drew a diagram and will post it in the pics to follow. There is a brass T and some rubber hose that clearly aren't stock.

RyansQuick6

The few seconds that the heat is on is when vacuum is building up. By default the blend door is open to heat and defrost, just in case the system fails, the car is safe to drive in inclimate weather.This proves threat the blend door is good and the actuator it's working. How it would seem to be a control problem. Although rare, the a.c. control panel may be the real issue..

fordforlife0225

ryanquick6, good to see you are still around.

here is what his mustang looks like


i circled what im concerned about in red. here is what a stock one looks like(with the exception of the procharger) but the area i circled is the same supercharged or not.


i took a temp gun and these are the temps i got off his car.

RyansQuick6

He doesn't have the stock tube there, but that's not the issue. Just from what you descibed about it working momentarily when the car starts leads me to believe it's the actual control panel in the dash.

My setup looks similar to his due to having to redo it all for the blower to fit. Mine looks a little cleaner though lol. If it were an issue of warm coolant getting to the core, then you wouldn't have pulled those 100*+ temps from the heater hoses at the firewall.