Fiesta Heater Circuit Component

[Hillhill]

Hi I'm new here and have searched here and everywhere as deep as I could to find an answer, but to no avail so I'm gonna start a new thread. I own a lovely 99 Fiesta Zetec and know that they suffer from a recurrent heater problem. The first time it failed the heater wouldn't warm and I froze in winter up so I changed the control solenoid valves (lots of posts on that) and that cured it fine. The second time the heater wouldn't turn off and I was roasted continuously - traced it to the heater control printed circuit board (having smelt burning electronic component smell), got a secondhand one, swapped it in and that cured it. The old board definitely had a burnt component on it. Some kind of surface mount transistor/thyristor (controls the valve using pulse width modulation I believe). Now again I am being roasted so as I have a spare board and I want to replace the burnt-out component first but I cannot find a replacement or even any spec on the part - I suspect the number on it is a Ford part number. It says PH89 52-10A and it probably costs less than a pound compared to the £40 quoted for a whole spare panel (they won't separate the board from the whole unit for me!). Can anyone suggest a replacement component I could use here? It doesn't have to be a surface mount - I could wire in anything provided I know what the pinout is of the old one and the replacement. Sorry to post such a long first post and that it's a bit electronical (I'm an electronic engineer by trade), but if we could get a fix for this I'd happily share what it is in more layman's terms and I know from my searches that it would save a lot of people a lot of money if they can wield a soldering iron! Thank you!

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[keithaird]

Hi.
Did you get any reply with help on this item?
I have the same problem though I've bought a second-hand unit, replaced it with still no joy - roasting slowly constantly still!
kaird@scmf.co.uk

[tabetha]

I've never seen one of these boards, but it won't be a ford specific component, just not cost effective, when there are alternatives available for pence that do the job perfectly.
It is also very unlikely that identifying numbers would not be on it, anyone give me a number and I'll do some research.
The only thing is, whatever caused the malfunction of this component to start with is still present, so it must be assumed that it wasn't particularly suited to start with, so a different version could be found.
tabetha

[Hillhill]

I have a working heater now. After my experiments with replacing the component itself - tried a n-channel MOSFET- and it too frying - I gave up and put a new board in and once more that too fried straight away. I thought my solenoid valve set was OK as it was brand new earlier in the year, but I took it out anyway and found it to be soggy and shorted - hence probably causing the excessive current and thus the blown component. In the end I refurbished a previous solenoid set, put that in and then got another replacement circuit board and I now have a sensible heater. I intend to monitor how much current the solenoid actually takes and fuse that wire with a sensible fuse to prevent further blowing of the expensive circuit board! (Job for the summer!)

[Hillhill]

Tabetha - The only identifying numbers on it I quoted in my first post - PH89 52-10A and I concluded, by drawing out the circuit, that it was probably an n-channel MOSFET so I tried matching it - there were very few out there that had a similar profileand came up with one by RHOM... RK3055ETL (8A Id max - Farnell order code 1680361) but that fried before I had the chance to see if it would work with a good solenoid set!