Hey Guys

Its been a long time but as you know I've just gotten to a point of being social after my wife passed in March. Thanks again for your condolences.

Now to my issue. My Aero lost heat some time in January and I'm just getting to it. I've done the following.
1. Checked both hoses to heater core..Both are hot after warmup.
2. Flused, cleaned and refilled system with new coolant.
3. Checked for operation of Thermostat - seems good.
4. Checked door that opens and closes to divert air to heatercore. working.

I have noticed the temp gauge will go from normal to cold intermittently, and this is during drive times of 30 to 120 minutes to work and running errands.

I'm stumped!

 

The fluctuations in the temperature gauge could be a sign that you have trapped air in the cooling system. This COULD cause the heater core not to heat up. But you said the hoses are hot after the engine warms up, so that means hot water is getting to it. But if it was working, one of the hoses should be hotter than the other as some of the heat should be dumped in the heater box.

Which door were you looking at? The heater door is in the heater box, in front of the core, so it's impossible to see without taking the box apart.

Other possibilities include the core is clogged enough that water flows through only parts of it, or the seal around it has rotted away and is allowing most of the air to bypass it.

If you installed one of those T fittings from the cooling system flush kits into one of your heater hoses, you can use it to test the core. Pull the end of the T going to the water pump, plug it with something, then attach a garden hose to the fitting and try to push water through it. Basically it's like using the kit to flush the cooling system, but you're forcing water through the core. It should flow freely.

The only way to check the seal around the core is to open up the heater box from under the dash.

One of the members of this forum found lots of leaves clogging the pathway.

 

I vote for the blend door not functioning. Check those plastic vacuum lines. At their age they crack very easily, but they can be spliced with a short piece of rubber vacuum hose.

 

With the temp gauge: "I have noticed the temp gauge will go from normal to cold intermittently, and this is during drive times of 30 to 120 minutes to work and running errands." I my opinion; the Thermostat is failing in the open position and not letting the water to get warm enough to produce heat.

 

bring the engine to temperature, then while you watch the HEATER VALVE in the engine compartments, have someone else turn the TEMP **** to cold and then to hot, to see if the HEATER VALVE opens and closes, which is something you can see but it happens too fast for you to do it by yourself.

The HEATER VALVE in a 4.0 liter is different from the one in the 3.0, make sure you have the correct valve.

 

I will remove the interior box around the heatercore and check for leaves and stuff. I could not locate the heater control valve that was mention, but I did locate it on my friends 1997 Aero with the same size engine. It doesn't seem to bee there on my 1990. I'll go to the manual.

I will keep you guys posted on the progress.

 

1) you can remove the Fan Resistor and then you can stick a vacuum cleaner through the hole to clear any grime in the heater BOX.

2) all cars have a Heater Valve or SERVO, also known as a "water diverter". In the 4.0 it is located behind the Air filter box, and to the left of the A/C Accumulator bottle.

3) if you find it, make sure the Heater Servo/Valve is not installed in the wrong orientation: The Vacuum Actuator is made of gold anonized metal, the rest of the valve is black ABS plastic.

4) the Correct orientation is for the Vacuum Actuator to be towards the firewall, at a 45 degree angle, so that the vacuum elbow connects to the actuator at the lower point of the actuator and close to the air filter box.

It is easy to install this Heater Valve incorrectly if you are not paying attention, the result is no heat.

 

I don't know which Aerostars came with a heater control valve that controls the flow of coolant through the heater core and which didn't. My 97 3.0 has one. It's next to the accumulator/drier right before the hoses go through the fire wall. It's vacuum controlled and if you have someone operate the temp control, if it's working, you can see it operate.
But my 87 3.0 DOES NOT have any such thing. If the engine is running, the coolant is flowing through the heater core, and it even bypasses the thermostat. As soon as my temp gauge starts to move, I start to get warm air. The outlet air temperature is controlled by the variable blend door that routes the air flow through the evaporator or the heater core. Nothing else.
It seems to me that this difference occurs because of the year, not because of engine size.
I just checked Advance auto parts and they don't list that part for a 91 4.0.

BTW. if you can get the fan out it affords better access to clean out leaves and such.
Sometimes the low pressure steel line is in the way.

 

Neither my 1990 nor 1991 4 liter Aerostars had heater control valves, so I'm guessing it came later.

If your van has air conditioning, the AC core will be just inside the fan enclosure, so you really don't have that much access to the heater box through the fan hole. But it's a good idea to clean that out while you're there.

 

all Aerostar, all cars have Heater Valves.

 

Aerostars, like most passenger vehicles, use a blend door to control in cabin air temperature. Works be controlling the amount of air that passes through the heater core and the amount of fan air bypassed around the core. Adjusting the TEMP **** changes mix which sets the temp. of air delivered.

The coolant control valve on later Aero's is located in the engine compartment near the firewall and over the pass. side fender. Prevents hot coolant flow when the A/C is selected, making for higher cooling efficiency. Cable actuated.

 

My 1990 has dual AC, so maybe the rear heater has a control valve, though I've never seen the control line for it, but the front definitely does not.

My 1991 only had front AC, and it definitely did not have a heater valve.

 

the Rear Heater or "Auxiliary Heater" has a heater valve located below the van, driver's side, looking straight down from the gasoline filler. it looks like this:

 

if you remove the Fan Speed Resistor shown in the picture, (ignore the red arrow), there is a hole large enough to insert a thin vacuum cleaner attachment and get most debris out.

 

I think I've figured this out.
It appears that the heater control valve located next to the A/C accumulator made it's appearance in 1994. As 96_4wdr pointed out, it was put there in an attempt to increase the cooling efficiency when the A/C is on. This coincides with the introduction of R134 and the reduction of the amount of refrigerant in the system that resulted in less efficient A/C systems.