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Ford heater control valve failure modes

Several Ford models - Puma, Ka, etc. - are fitted with a heater control valve similar to

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It controls the flow of hot water from the engine to the heater matrix. A solenoid-operated plunger either allows the water to flow to the heater (hot) or diverts it back to the engine (cold). When the heater control knob is set to hot, the solenoid is de-energised. On the cold setting, it is energised. AIUI, on intermediate settings the solenoid is cycled on and off to reduce the flow through the heater but not stop it altogether.

If the solenoid - or the logic and/or wiring controlling it - fails, the heater will be hot regardless of the position of the temperature control knob.

But what if the heater is *cold* regardless of the knob setting? This suggests either that the solenoid is being energised when it shouldn't be - or that the plunger is stuck in the 'cold' position. The first of these can easily be eliminated by removing the cable.

My wife had been complaining about a permanently cold heater on her Puma for a while, and I decided that the most likely culprit was the HCV and fitted a new one - which cured the problem.

But I was curious to know what was wrong with the old one, and carried out a post-mortem on it. With it in bits, and connected to a 12v supply, the solenoid worked ok - so that hadn't failed. [A failure of that wouldn't have fitted the symptoms, anyway]

When I re-assembled it, I found the the seal on the plunger was being pushed hard against its seat (i.e. in the cold position) without the solenoid being energised. Further examination indicated that the plunger had mysteriously increased in length. The axis of the plunger is in two parts - a sort of spool with a conical seal at one end and a disc at the other, and a smaller diameter spindle with a metal cylinder at the far end which sits inside the coil of the solenoid. The non-solenoid end of the small spindle is an interference fit in a hole at the seal end of the spool.

See the photos at

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to see what the innards look like in the hot and cold positions. What appears to have happened is that these two parts had somehow worked apart - thus increasing the overall length of the plunger assembly. I attempted to remedy this by using gentle pressure in a vice to try to push the two ends together - to no avail - using reasonable force it wouldn't budge and, being plastic, I was loath to use more force. In the end, I thought "what the hell" and rested the seal end of the spool on the jaws of a vice without tightening it onto the shaft, and then gave the solenoid end a few sharp axial blows with a hammer - amounting to what I regarded as *unreasonable* force! It did the trick, and drove the small shaft back into the end of the spool so that, when I re-assembled the valve, the spool moved back and forth correctly as the the solenoid was turned on and off.

This was a failure mode which I hadn't anticipated but, form the number of reported instances of heaters being constantly cold, I suspect that it may not be uncommon. Has anyone else come across it?

Reply to
Roger Mills
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yes, but it is not worth messing about with, by the time they fail the plastic is brittle anyway. the valve is operated by pulses to operate it, IIRC

Reply to
MrCheerful

Always surprising how a bit of vibration can make things move when they appear to be very much stuck.

Reply to
Peter Hill

The body of the valve was certainly brittle. One of the inlet pipes broke off when I was undoing the clip to remove the hose. Just as well I had a new valve to fit! But the plastic internal bits withstood a hell of lot of punishment and still remained intact. Had they been brittle. they would have shattered with my hammer blows. [My late father had used to have an expression along the lines of "If you can't mend it, make sure that nobody else will be able to!"]

Sort of. I've seen some descriptions which claim that it has a stepper motor. I had assumed that it would be at one end of its travel for hot, and the other end for cold, and somewhere in between for intermediate temperatures. But it ain't like that! It is simply a solenoid which moves the plunger to one of two positions. In one position, all the water goes through the heater and in the other it all goes through the by-pass. My impression is that intermediate temperatures are achieved by turning the solenoid on and off - which I guess is akin to your pulsing

- in order to achieve a sort of time division multiplexing with the water going through the heater for some of the time and through the by-pass for the rest.

Reply to
Roger Mills

Indeed. Judging by the amount of force which I needed to use to push it back in, I'm amazed that it worked its way out unaided.

Reply to
Roger Mills

if you put a lamp across the lead (with power on and turn the heater to hot) you will see the pulses, and with the lead connected, but no water/pipes, you will hear it clicking and see the valve move.

Reply to
MrCheerful

The idle air valve on my car is a solenoid, a coil and spring loaded plunger. It is controlled by Pulse Width Modulation (PWM). As the pulse gets longer the valve opens more. The mass of the mechanical plunger is too large to respond to the 1000's of pulses each second so it moves to the average position that the pulse width sets.

Measured with a multimeter all I see is a voltage.

Reply to
Peter Hill

OOI, what car? Because that's not how the Ford IACV solenoids work.

Chris

Reply to
Chris Whelan

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