Does anyone experienced amp spike on powering up the fan blowers?
From the look of it - it’s quite high, event the headlights going into “dimmed mode” for the fraction of the second, blower fans are not starting from low and med setting (spike still exists on energizing the AC module). From the charging gauge I can see thst the voltage drop during power-up is massive (down to 10ish Volts, with engine running on idle). After switching to ‘high’ everything works, also while switching down to lower settings…
Looks like transistors/resistors, however after changing blower fans (second hand set) - issue is still present.
Conclusion - each sets of blowers has broken transistor or the AC modue is crap. Unless there is a simple relay responsible for the spike (not sure how’s that possible)
Does anyone have similar experience? 1988 XJS 3.6.
GROUNDS…OLD BATTERY…WEAK ALTERNATOR…SHORTING RELAY .
Its 40 years old, go through it all. Start with a fresh battery or fully charge your battery , clean and upgrade grounds, then test the components.
Good luck as always…OLD XJS v12 create loads of heat , 40 year old wires arent happy under heat.
gtjoey1314
Yes! I got the same thing, although I haven’t tested it in quite a while, just drive without fans on.
I’m starting to think it has something to do with my auxillary fan, because on my 1988 when I turn on the blower fans, the auxillary fan automatically comes on. It is now constantly blowing the fuse for the fan/horn. So I think my aux fan is messed up, taking way too much amperage to turn.
I would try disconnecting your aux fan and see if the problem persists.
my aux fan is a Spal only 1 year old. But I did spill some fluid on it shortly before all this happened, and I notice that it’s hard to turn by hand, and if it does turn instead of blowing the fuse, takes about 10 seconds to finally spin at full speed.
But regarding XJSBangers, yeah, if it’s original fan that could be it?
A coincidence perhaps, but after the weird experience that I had (and possibly totally unrelated) I can’t help but think that both of you guys might have a climate control module failure. It’s buried on the right side of the tunnel. The problem is, HOW DO YOU TEST IT?
blower fans have a small electronic board inside, with a diode and a transistor, to get the low and mid setting
the “high” setting doesn’t use this bit, but if switched by a relay
imho, the internal card is busted, probably the big transistor is shorted
Don’t know exactly when the Delanair III came into being, and if it’s any different from the Mark II in that aspect, but the thing is that as soon as you turn the fans On, i.e. you turn the climate control On, the A/C turns automatically On as well, and therefore the Aux fan.
In other words, it’s normal.
I thought the Delenair III system was a true climate control, and only fired up the A/C side of the system once the coolant temp had reached a certain value.
We can exlude battery issues and relay shorting (as this would be against design logic). Transistors are usually not being resurrected after death, so it is unusual to have it back after starting from high settings. With 3.6 engine and 115amp alternator - Volt gauge dropping below battery lever is definitely not normal.
The theory with aux fan is really interesting, especially with spike time shorter than regulator response in alternator…
Considering that AC module is damaged - disconnecting aux fan plug will be nice thing to try…
In the early Mk III versions, at least, the refrigeration system/compressor was engaged whenever the climate control system was in operation, regardless of mode selection or temperature selection…just as it was with the older Mk II system. All incoming air was first refrigerated then heated when necessary.
As years went by there were some changes. I think the last few model years had a economy or vent feature which allowed the compressor to be turned off.
Some convertibles were wired so that the compressor was always on, period. Even if the mode selector was turn “off”. The idea was to keep the fuel cooling capability active at all times.
Normal operation for the XJS up to a point, yes. Beginning circa 1989 the aux fan circuit was changed; there were various iterations after that. In some cases the aux fan circuit was divorced from the climate control.
For power switching they may have used MOSFETs instead of bipolar transistors. Their failure mode is closed, so would be switched on all the time if they broke.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
16
Kirbert, yes it has - with every Bosch 115amp alternator by default. Not sure how that relates to the current spike reaching almost short-circuit values… ? It should work in favour of the circuit design. Guessing you’re suggesting it disconnects the alternator somehow on AC energizing?
Any ideas highly appreciated.
Short update - just checked and aux fan can be exluded. However, there seems to be a relay under lower-right ‘corner’ of the steering wheel that gives fast repeat click even with both fuses from blower motors out. Shitty relay or AC module…?
Switching inductive loads causes huge spikes in voltage and current.
At startup, the current drawn is infinite but it drops down exponentially. The coil of wire then acts to keep current flow constant. At switch off, the exact reverse happens.
The typical way to ameliorate this is to switch the inductive load through a transistor, but have the transistor’s control signal have to charge up a small capacitor in the process. This delays the inrush of current because the transistor is turned on more slowly and so the top of the spike is trimmed.
This is the same principle behind the fuel pump circuit board which acts as a points saver for SU pumps, but the current switched for the blower fans is so much higher. See the circuit diagram higher up the thread XK Tranistorized Fuel Pump
that both of you guys might have a climate control module failure. It’s buried on the right side of the tunnel. The problem is, HOW DO YOU TEST IT?