Question about 2003 Ford F350 Super Duty DRW SuperCab

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Heater valve is not getting any vacuum

Just purchased a used 2003 F350. The heater will not work. The hot water valve is not getting any vacuum to it. The rheostat ohmed out to be operating. Voltage at the wiring plug to the rheostat checks out to 5 volts. I Jumpered past the rheostat with no results. Can you tell me where to find the heater vacuum controller?

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Try removing the vacuum hose at the back of the vacuum pump start the engine and see if you can feel it pulling a vacuum it should **** you're finger in a bit or if you have a vacuum gage hook that up and see what it readsshould be at least 12-15 in vacuum. Also is the heat stuck in defrost mode ?

Posted on Jan 08, 2009


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Why does my heater blow cold air?

Usually 1 of 2 reasons. Some cars have a water control valve which makes hot water go through the heater core. The water valve is operated either by cable or Vacuum control.

Feel the 2 water lines from the heater core when the engine is hot. They should both be hot with the heat turned on. If one is cooler than the other, it is a water control valve problem.

If both lines are hot, then you have a problem inside the car and under the dash. The air flaps in the duct work are not changing the flow of air. You could have a slipped cable by the heater flap or a Vacuum pull-down is not working. Operate the heater control and see if the heater cable moves anything or not.

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Heater only blows cold air vent blend door working fine

Here we go.
Raise the hood and remove the radiator cap.
Start the car and heat up the engine, usually takes about 5 minutes.
Turn on the heater full blast.
At this time, be sure your radiator is full of coolant, because a low radiator will drop the coolant so low the heater will get no water, it could be "air-locked".
If the collant level is low, add coolant and run the engine at a medium speed for 5 minutes to "burp" the air out of the heater hoses.
Feel the heater hoses to see if they are hot. They should be.
Feel the radiator hoses to see if they are hot. They should be.
If the radiator hoses are not hot, you may have a defective thermostat, it it might be stuck open.
If so, the heater would not get hot, because the motor is not.
If the radiator hoses are hot, and the heater hoses are not, likely the hot water is shut off to the heater.
There is likely a control near the firewall that is either controlled by a wire cable or a vacuum line.
This control valve has 2 heater hoses connected to it, one incoming and one outgoing.
Often, the wire cable or the control valve itself will stick due to rust or corrosion, or disuse.
If it is vacuum controlled, you may not be getting vacuum to the control valve, or again, the control valve may be stuck closed.
Sometimes these controls can be freed up with penetrating oil, sometimes they are too far gone to repair, must be replaced.
If you can fix it with penetrating oil, you may need to do that once a year.

Jan 19, 2013 | 2003 Ford Explorer Sport Trac

1 Answer

My heater on my F350 does not seem to be working properly. When I take my foot of the gas....the heater pumps cold air. What is my problem?

if the heater fan is sill blowing then the only thing is maybe the water pump is faulty. Feel the hoses if you can get to them for the heater core when its idling.. If one cools down when you idle and heats up when your reving up the motor I would suspect a coolant flow issue, I have seen heater cores clog or become restricted so reving the motor would push more hot water thru You may have a control valve on one of the heater hoses going to the motor that may not be fully opening .
Now it they are both hot and stay hot then I would heater box as being the issue, I wouldnt suspect the control as being at fault.

Dec 01, 2009 | 2003 Ford F350 Super Duty DRW SuperCab

1 Answer


If you are sure all the things you fixed are working good then I would say its the heater control valve around $30 and looks like this hope this helps


Nov 20, 2009 | 2003 Ford F350 Super Duty DRW SuperCab

1 Answer

All of a sudden, my 2004 Ford Taurus heater control doesn't work. Hot air ALWAYS comes out, no matter where the temp control is set. Even if set in AC mode the air is VERY HOT! Help!

The valve (called the heater tap) which controls the hot water flow works from engine vacuum. The climate control unit turns vacuum on to close the valve and turns vacuum off to open it, if the vacuum tubing or vacuum service valve has failed, the tap will be open allowing hot water to flow. The same result applies if the heater valve itself has failed (which they do --regularly) Trace the water hoses from the enginebay firewall under the hood and you should find the valve. Check for cavuum at the valve with the climate control set to its coldest setting. If you have vacuum at the valve, replace the valve. No vacuum points to the loss of vacuum source or a faulty vacuum service valve with will be electrically operated from the climate control. Trace the vacuum hose from the heater valve back to the vacuum service valve and check if the valve has vacuum supplied to it. No vacuum means a vacuum hose has blocked, has a hole in it or has been removed from the manifold. If the electrical valve has vacuum, check for power. If power is present but still no vacuum at the heater tap, replace the service valve. If power missing, check fuses. If both wires to the valve show power present, have the climate controll unit checked by a professional..

Oct 31, 2009 | Ford Taurus Cars & Trucks

2 Answers

There is no heat come out of my heater for a 2003

It's more likely you need a new thermostat. A bad thermostat will impact the heater. If it's the heater core, you often will get a pool of coolant in the inside of the car by the passengers floor. You also may get a mist when you select the defroster.

Oct 25, 2009 | 2003 Buick Regal

1 Answer

Heater in Cab will not blow hot air

heater core might have setament or scale built up in it. needs to be flushed out. maybe thrmostat bad. i would try flushing heater core out first. use garden hose flush both ways, also before you flush it mix up alittle beaking soda and water and pour in heater core and let set for a while so it can loosen up the scale and setament then flush both ways until it runs clear.

Jan 14, 2009 | 2003 Ford F350 Super Duty DRW SuperCab

2 Answers

I am looking for a website to see schematics of heater core and associated parts, ie; heater control valve, vacum control etc.. any ideas, thanks Andy

If you go to you can purchase a subscription for the repair info on that vehicle. The subscription is good for 1 year.

Dec 23, 2008 | GMC K1500 Cars & Trucks

1 Answer

Defrost will not come out vents

Check your coolant level first. Next check your heater control valve. With engine at operating temp and heater on high, do this:

1. Heater hose from water pump should be hot (if not, water pump may be dead or thermostat is stuck closed)
2. Heater hose from thermostat housing should be hot (if not, thermostat may be stuck closed or water pump is dead)
3. Heater hose going to heater core should be hot ( if not, heater control valve is not getting vacuum from heater control unit, or valve is broken)
4. Heater hose returning from heater core should be hot (if not, heater core is blocked, undo both hoses to core and flush with water hose until clear)

Test thermostat: with cold engine cranked, watch water temp gauge. As it gets hotter and hotter, when the thermostat opens, the temp should drop suddenly and then go back up.

Test water pump: with engine at operating temp. Squeeze top radiator hose tight, when you release it, you should feel/hear a surge of water. It is much like when you pinch a water hose closed and release it.

Test vacuum from heater control unit to heater control valve: undue vacuum line from control valve. It should have a vacuum when pressed against you skin in addition to releasing the actuating arm on the control valve.

If there is no vacuum, a quick fix will be to disconnect the plastic actuator from the silver arm on the heater valve. This will let the hot water to always flow to your heater core.

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