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Heater Control Valve Replacement
The heater control valve (HCV) controls the flow of hot coolant through the heater matrix, which is a small radiator that heats the cold air as it enters the car interior. The HCV does this by periodically opening and closing. It repeatedly allows hot coolant to flow through the heater matrix for a certain period, and then blocks the flow of coolant for a certain period. Thus the temperature of the heater matrix is governed by how much time the HCV spends in the open position, and how much time it spends in the closed position. These time periods are controlled by electronics in the heater control module, which is the control panel below the car stereo that contains the heater temperature control knob.
Figure 1 – The heater control valve
The HCV is a notoriously unreliable part. When it fails, the car’s heater usually sticks on either hot or cold, regardless of the position of the heater temperature control knob. Before the HCV fails completely, the heater temperature may fluctuate erratically between hot and cold for a period, before eventually sticking on either hot or cold.
There is also strong evidence to suggest that the plastic from which the HCV is made deteriorates over time and becomes brittle. Several Pumapeople members have reported pipes snapping off the HCV, or even complete disintegration.
This article describes the procedure for replacing a failed heater control valve.
Removal of the heater control valve will result in some coolant loss, although because the HCV is at the very top of the coolant system, loss should be minimal. To minimise the amount of coolant that is lost, wait until the engine is cold before carrying out the procedure. Never allow coolant to come into contact with either the auxiliary drive belt or the cam (timing) belt, as contamination can lead to premature belt failure.Parts required
A new heater control valve (available from the parts counter at your local Ford dealer)
Tools required
A Phillips (cross-head) screwdriver
A pair of mole grips (aka vise grips, or locking pliers)
A Large flat-bladed screwdriver
Step 1 – Detach Bulkhead Extension Panel
The bulkhead is the wall of metal at the rear of the engine bay that separates the engine bay from the interior of the car. The heater control valve sits on top of the bulkhead, under the windscreen, roughly in the middle. Attached to the upper part of the bulkhead is the bulkhead extension panel (aka scuttle board), which is a flimsy black piece of trim that runs the whole width of the engine bay. The HCV is behind this panel. More experienced DIYers may be able to replace an HCV without removing the bulkhead extension panel, but if this is your first time, you may want to remove it for easier access, and so that you can see what you’re doing.
First, remove the long rubber sealing strip from the top of the bulkhead extension (see Figure 2). The strip runs the whole of the width of the engine bay, from wing to wing.
Figure 2 – Remove rubber seal
The next thing to do is remove all of the screws that secure the bulkhead extension panel to the bulkhead. Most of these screws are easily accessible, but there are a couple that are hidden by the coolant expansion tank.
Remove the screw that secures the coolant expansion tank to the bulkhead (see Figure 3).
Figure 3 – Remove coolant expansion tank screw
Detach the coolant expansion tank from its bracket and pull the tank to one side (see Figure 4). To detach the tank, pull it upwards and off the bracket. You may have to insert a large flat-bladed- screwdriver into the tank’s slot to release it from the bracket.
Figure 4 – Detach the expansion tank from its bracket
Once the tank has been detached, there are two screws to be removed – one that was underneath the tank (see Figure 5), and one behind the windscreen washer filler cap (see Figure 6).
Figure 5 - Remove screw that was under expansion tank
Figure 6 - Remove screw from behind windscreen wash filler
Remove all of the remaining screws that attach the bulkhead extension panel to the bulkhead. Once all of the screws have been removed, you should be able to pull the bulkhead extension panel away from the bulkhead sufficiently to reveal the heater control valve (see Figure 7).
Figure 7 – Pull the bulkhead extension panel away from the bulkhead
If you can’t pull the bulkhead extension panel away sufficiently, it may be necessary to detach the metal plate from the panel (see Figure 8).
Figure 8 - Remove metal plate from bulkhead extension
Step 2 – Remove Old Heater Control Valve
Remove the rubber cup that protects the HCV’s electrics (see Figure 9).
Figure 9 – Remove the rubber cup
The HCV has four hoses attached to it – two at the front, and two at the rear. Using a pair of mole grips, release each of the hose clips and slide them up the hose, away from the HCV (see Figure 10). Release the clips by squeezing the two tabs towards each other with the mole grips.
Figure 10 – Release the hose clips
Now pull all four hoses off the HCV (see Figure 11). If the hoses are tight, you may find that twisting or wiggling the hoses helps. Ensure that you remember which hoses were attached to which pipes on the HCV.
Figure 11 – Detach the hoses
Detach the electrical connector from the HCV by depressing the metal locking clip with your thumb and pulling the connector plug (see Figure 12).
Figure 12 – Detach the electrical connector
The HCV can now be removed. Figure 13 shows the HCV removed.
Figure 13 – The HCV removed
Step 3 – Fit the New Heater Control Valve
Slide the new heater control valve on to its platform (see Figure 14).
Figure 14 – Slide the new HCV into position
Reconnect all four hoses to the HCV and slide the hose clips back into position.
Refit the electrical connector.
Refit the rubber cup over the electrical connector.
Now is a good time to test the new HCV for leaks (before you refit the bulkhead extension panel). To do this, refit the coolant expansion tank on to its bracket. Check the coolant level and top up if necessary. Set the heater temperature control knob to maximum (hot) and start the engine. While the engine is running, check all four of the HCV hoses for leaks. Note that you haven’t yet tested the coolant system, so keep an eye on the engine temperature and be ready to cut the engine if it gets too hot.
Refit the bulkhead extension panel (detaching the coolant expansion tank so that you can refit the two hidden screws).
If the metal plate was detached from the bulkhead extension panel, refit it (see Figure 8).
Refit the coolant expansion tank.
Refit the rubber seal to the top edge of the bulkhead extension panel.
Check the coolant level, and top up if necessary.
Step 4 – Test the Coolant System
Whenever you carry out any work on the coolant system, you should always run a test to ensure that it is still working correctly. This usually involves starting the engine and waiting until the radiator fan has started and stopped twice (two fan cycles). A close eye should be kept on the engine temperature gauge, and you should be ready to cut the engine if it appears to be getting too hot.
If an airlock has been introduced into the system, it may be necessary to bleed it. See this post for more details.
This post has been edited by Mountain Lion: 12 May 2007 - 08:41 AM
