Heater Control Unit Required

[oliverkelly]

Anyone know where I can obtain a second hand or reconditioned Heater Control Unit or where I can get it repaired.

Mine has packed up, and only the cold fan works.

The fan had seized and I expect that this caused the problem with the Heater ECU.

A new one is £240 + VAT! Why TVR need to have a load of electronics to control the speed of a fan I have no idea.

[david beer]

Slightly different but my 99 Griff 500 heater fan did not work and looked inside my electronic module and found the mosfet blown, cost pennies.Yours of course may be completely different. If you can find someone to open it up, the first check is always a "visual". They then could at least do that for you without any service manual.

[lesp]

Hi Oliver, got similar problems with the control unit in my Cerb. Is the cold fan the only thing that works or do the heated rear window and air con still work as well ? As David says, it could well be the MOSFET that controls the fan speed that is faulty. Easy to change if you're ok with desoldering / soldering onto a board and only costs about a pound.

[oliverkelly]

The rear demist stopped working some time ago, and the hot fan quite recently. I am not too worried about the rear demist though.

I am quite happy with soldering. When I measure the voltage accross the cold, it lowers as the knob is turned, but this doesn't happen for the hot. Does that mean it is likley to be the Mosfet ? Or does the voltage only lower if the fan is actually turning ?

Any help in diagnosis would help.

Oliver

[gazzab]

are you sure the rear demist isnt just a coincidence?
Mine stopped workign and so I checked the connections at the edge of the rear screen. Pushed them on properly and then it was ok.

[lesp]

Apologies if I'm stating the obvious, but have you checked that the hot fan is actually working ? If you remove the control box and then connect the two pins together for the hot fan in the wiring connector, the fan should come on at full speed (with the igntion on). Without the box in place I get 12v across the two pins, same for the cold fan pins. Presumably, it's this voltage you see decreasing on the cold side when you rotate the knob ? Or are you looking at the voltage applied to the MOSFET to control it ? All the above assumes that your system is similar to the one in my very early 4.2 !

[oliverkelly]

Yes I checked the fan was working. It was actually seized, which I imagine caused the problem with the control unit. Once I freed it up, it worked fine when 12v is applied to it, but still didn't work using the control knob.

An electrician at the factory told me they control it through the return (?) side, and that there is always 12v at the fan.

I have ordered a replacment control unit from a breakers yard, so I will see if that cures the problem. Half the price of a new unit !

The voltage I saw dropping was accross the Mosfet itself with the control box open. Which would also be the two pins that go tot he fan.

[lesp]

I had trouble getting a secondhand replacement for mine, hence I'm trying to fix the old one. The bottom board seemed to be common, but the top board was completely different to anything else they had. (I think it was that way round). Sounds like it's too late now, but changing the MOSFET would probably have been worth trying.