No more heated air.....

[guy]

1997 4dr AWD

Engines gets up to temp just fine, but (all of a sudden) can no longer get heated air out of any blower vents, no matter which setting the selector switch is set to.
Fan works fine on all settings, and A/C works fine too.

I bought a Chilton's manual, which is pretty worthless.

I suspect its either the solenoid/vaccum thingie for the vent door which allows air to flow over the heater core, or maybe there's a solenoid valve on the coolant inlet to the heater core?

How do I isolate and fix?

Any help is appreciated!

Thanks

 

[yob_yeknom]

Is the vaccuum line to the heater valve still connected? Do you know that the heater valve is working? (test with a hand vaccuum pump) Try the easy stuff first and let us know what happens.

 

[guy]

Testing the heater valve...

Thanks for the quick response.....

Sounds like a pretty good plan. A couple of questions though:

Where is the heater valve? (I think I saw in another post that it's on the firewall, on the driver's side, and can be identified as the valve that has three coolant hoses running to/from it - is this correct?)

Should I try to put vacuum directly on the valve, or should I try to find the line inside the passenger compartment and drive it from there? If so, where does it go to in the passenger compartment?

I have a brake bleeder that I can probably adapt to test the vacuum line. Will that do?

Also, can you recommend a decent manual? I'm spoiled - I had an '88 BMW (most bulletproof car I ever owned), and a Bentley manual (best manual I ever saw). What's the best manual for the Explorer?

Thanks again,
Guy

 

[leenjen]

Re: Testing the heater valve...

Originally posted by guy

Where is the heater valve? (I think I saw in another post that it's on the firewall, on the driver's side, and can be identified as the valve that has three coolant hoses running to/from it - is this correct?)
yes, you're right

Also, can you recommend a decent manual? I'm spoiled - I had an '88 BMW (most bulletproof car I ever owned), and a Bentley manual (best manual I ever saw). What's the best manual for the Explorer?
a lot of people swear by the Haynes manual

 

[guy]

It's not the heater valve....

I checked the heater valve - it moves in and out (driven by vacuum) on its own when you change the outlet selector from "off" to floor, floor/defrost, defrost, etc. Also, both the inlet and outlet hoses going into the firewall are hot, so it looks like hot coolant is getting to the heater core.

Therefore, the problem has to be with the vent flap regulating airflow over the heater core.

Since I have a cableless control head, there's no cable going to the flap. Instead, the temp knob/selector is a potentiometer that somehow must drive the flap position via a motor.

Anybody know where/how you get access to the motor that works the flap? Also, does anybody know what the resistance range is that I should be reading over the temp control switch potentiometer?

Thanks,
Guy

 

[yob_yeknom]

.................................................
There is a flap though that opens to let the warm air into the vehicle. It is also moved by vaccuum. It is possible that it is stuck in the closed position. Here's a way to test to see if it is working: With the engine running, turn the selector to the vent position. Do you hear the vaccuum hiss of the vent opening? Wait a few seconds and turn the engine/ignition off, but leave the selector on vent. Wait a couple of seconds and turn the selector to off. Do you hear the hiss of the vaccuum letting off and the vent flap shut? You should hear the vent on the passenger side.

As far as I know of, that's how it all works. Let me know if I'm wrong. ....I think I was...

Fill us in on what happens.

 

[guy]

arghh

the flap you mentioned is working OK - if you release the glove comparment so it flops down, and look in/under the dash, you can see it operate.

also, what converts the temp knob setting to the vacuum signal that goes to the heater valve? i can see the back of the control head, and it looks like the only things coming off of the temp knob are wires (ie., no little grey vacumm lines).

anyway, the heater valve is definitely being activated by the vacuum line attached to it, but its only being set to its extremes - all the way in or all the way out. wasn't able to get it to sit halfway.

i set the control switches to defrost/max fan speed/max hot, and got no heated air out of the defrost vents. when i did this, the heater valve slide arm was fully extended, which i assume allows (or is supposed to allow) max hot coolant flow thru the valve.

next, leaving all the switches in the same positions, i put a clamp on the heater valve to force the slide arm all the way in. still no heated air. the air was absolutely stone cold - not one iota of heat to it.

Candidate diagnoses:
1) maybe the lever that the slide arm engages with has become disconnected from the actual valve within the heater valve (is this likely?)
2) there's some kind of blockage within the heater core (but i doubt this - i would think you'd get at least a little bit of heat)

Also, both the heater coolant hoses felt pretty warm. don't know how meaningful this is, though...

Help!

 

[Jason_25]

You said you can't get hot air to come from the vents. Can you get cold air to come from them?

 

[410Fortune]

You probably have already checked but your truck should have a hot water bypass installed on the heater lines running into the core (under the hood)
This is a vacuum actuated valve that diverts the flow of hot coolant so it bypasses the heater core.
Check that baby and make sure it is working, you can remove the two cooling lines on the engine side without losing too much coolant, to see the valve operate.

The heater core will still get warm but not nearly as hot as usual.

 

[yob_yeknom]

Maybe I misunderstood what my dad was saying about how everything works. (He was at work and couldn't go into detail, so I got a really brief discription.) He's asleep now, so I can't ask him.

Here's what I can tell from turning on the heat in my Explorer. The water apparently flows into the heater valve by the top hose going into it. (it should always feel hot when the engine is warm) It then goes into the heater core through the hose entering the fire wall on the right. (closest to driver's side) (it should get hot when you turn on the heat) It comes back out of the heater core through the one on the left. (it should be warm when the heat is on, but not as warm as the one on the left) If all is good there, then you know the hot water is making its way through the core.

Maybe we're not talking about the same flap here. Are you saying you can see the flap that lets air coming from over the heater core behind the glove compartment?

Another thing I thought of is do you know if anything like a plastic bag or trash or something got pulled up into the vent on the floor where the air goes in at? That used to happen a lot on my mom's old Taurus and that would cause it not to have heat.

 

[rustytr]

Wow, complicated... When the heat stopped in my Jeep when I was 16 I replaced the thermostat and Voila, heat.

 

[dwk55]

Do you get any heat at all? Before or after the engine warms up.

If no heat at all, its probably the heat blend door that has broken in the heat off position.

This is common for this year. The dash needs to be removed to repair this part.

 

[guy]

Heat blend door sounds like a big deal...

but, it also sounds like it might be the problem.

Do you know if the door can be replaced without removing the entire box assy containing the heater core & A/C evaporator?

Also, do you know where the vacuum line that drives the door originates from, and where under the dash it attaches to the box assy?

Thanks,
Guy

 

[dwk55]

Not sure where the vacuum line is.

I have heard that the whole plenum assembly needs to be replaced. The good thing is that the replacement part is made of stronger material so that it won't break again. I think it costs around $140.00. Most of the cost is in labor to remove the dash. This may cost up to $800.00 to repair if done by a dealer.

There is no other way to get to the plenum assembly. For what its worth, call ford customer service to complain, save your receipts, and maybe some day they will issue a recall. But, I highly doubt this.

 

[SnowLover]

Hey Guys,
Checked in this morning and found my exact problem being discussed! My '93 is experiencing identical problems, and I have verified all the door positions through the Chilton Manual (if it can be believed).
Tomorrow I plan to change the thermostat (again) and then look at the other issues.....frappin' Ford!

 

[SnowLover]

Okay- I changed the thermostat- it helped for a day or two, but it would never get warm consistently. I did verify that the old thermostat was sticky. I am about ready to jam some cardboard in front of the radiator and be done with it. Could it be the water pump is weak?

 

[yob_yeknom]

Are you sure the heater valve is working properly?
Have you ever flushed the coolant system?

 

[Positive Vibes]

I had a similar problem with my '94. Everything was fine except that it would only blow cold air. I was in Idaho at the time and the guy at the dealer new exactly what it was, but I cant remember the exact terminoligy. It was a round thing that went in one of the radiator hoses. God what was it called was it the thermastate?? It only costed me $2 to fix and around an hour of work. Its round about the size of a silver dollar and it basically controls the amount of circulation thru the hose. My truck is in the shop. I busted my driver side Radius arm and I dont have my Chiltons with my. If you don't have it fixed by tomorrow Ill get some more info for you!

 

[Jason_25]

Heater control valve maybe?

 

[Longs]

A basic point - you said that the heater inlet and outlet hoses at the firewall were warm. If your Explorer is at full operating temperature, say when you've driven it for 15-20 minutes, and the heater is "on", those hoses should be too hot to hold onto. They should be just about as hot as the top radiator hose is. My guess is that there's no way you could hold onto the top radiator hose without burning yourself - should be the same with the heater hoses, in and out. If not, you have a blockage somewhere - either the heater control valve is bad, or the heater core is plugged, or a hose has a restriction.

You could try removing the heater control valve from the circuit (replace with a short length of copper pipe just long enough to clamp the hoses onto) to see if that's where your problem is.

Diagnosing out there will be a lot easier than finding your problem under the dash...

Just a thought.