1973 AC Model 70 Invacar, Visitors & Occasional Distractions

The switch is so you can tell at a glance if the pack was charged or used, you’d flit it over when it was dead if you had a lot of batteries so you knew which ones needed charging.

Isn’t it funny how our brains work so differently ? I came to the same thought as “Rich” but big chunks of what you are doing on recent projects I don’t fully understand but do enjoy the write ups.
James

That's why places like this are so great, also why I have this thread for occasional distractions in addition to the rest of the fleet which I do try to keep on topic! People seem to find it interesting so I keep it updated.


Definitely wouldn't be the first time I've been bashing my head against a problem for a whole afternoon then had someone say "Why didn't you just..." and handed me a solution that solved the problem in five seconds flat.

Nope, the switch on these packs is simply a visual indicator, there's no interlocking or anything involved.

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Remembered the keyboard shortcut to get to the "fuel gauge" for the battery on the T1200 - function + sys req.



Also figured that this might be an interesting experiment.



Windows 3.0 is the last version that would run on an 8086/8088, albeit looking a bit strange on an inverted monochrome LCD with a bit of an oddball (640*200) resolution.

Runs a lot better than I expected to be honest. Bit sluggish when waiting for disc access but that's expected really.









To be honest I'm not really likely to use Windows for much...the MS-DOS Manager does a decent job of file management and all of the software I really need is DOS based anyway. I was mainly just curious to see how it ran on an 8086 machine.

Think the display really does show how it was really designed with text based applications in mind. It's not at it's best when dealing with graphics - but does a surprisingly good job of text. To be honest it's a lot more pleasant to use than the DSTN panel on the mid 90s ThinkPad I've got. Which is just utterly "meh" whether displaying text or graphics.

Replacement tips finally arrived today for the soldering iron so hopefully future work requiring it will be somewhat less frustrating...I really hadn't realised how knackered the old one was until I started doing delicate work with it rebuilding the power supply on the laptop shown above.

Few folks have asked me what iron I use elsewhere, same one I've had for about fifteen years now.



Iroda Solderpro 120, little gas unit. It's not as precise as an electronic one where you can dial in an exact temperature but you can very the power from virtually nothing through to about 100W, which has done everything I've asked of it so far. Using an electric iron with a cable in the way always feels really cumbersome once you're used to a gas iron.

Speaking of tools, I finally stopped procrastinating about it today and picked up a new lawn mower.





Initial impressions are that it feels well made. Quite a bit bigger than our old mower, will be curious to see how well it works - given that the old one was a kerbside find that cost me all of about £3 to get running it owes me nothing. It could be repaired - but has just got to the point that enough things need doing that it's just not worth it when there's something I really can't fully resolve - and that's that the grass collection box is missing. I've tried half a dozen times now to buy a new one but just haven't been able to get hold of one - so given it needs new rear wheels, replaced wheel bearing on one of the fronts, a couple of missing bolts replaced, ideally a new drive belt and a couple of cracks in the deck that are starting by the handle base repaired...it's just not worth it. Nothing wrong with the engine though...so I need to see if I can come up with something to do with it...current thought is "I wonder if I could find a suitable pressure washer pump head to hook up to it..."

Given the weather forecast over the next few days goodness only knows when I'll get to do the first test!

Despite the weather I managed to get TPA out for a run today.



Contrary to what it looks like in this photo there were very ominous looking storm clouds just out of frame to both sides and behind me.

Never ceases to put a smile on my face this little car, really does drive far better than she has any right to.

Still not quite how I managed to dodge all the worst of the weather...it was all around me pretty much the whole time.

Another brief Segway because I had to bust out the screwdrivers, multimeter and wake up a few brain cells to convince a grumpy piece of equipment to do its job again, and engineering type challenges seem to be well received here.

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Ever since I got it there has been something slightly funky with the control system on this one air conditioner. Never bothered too much about it at the time given the price of it and being a unit from the early 90s and that it was clearly an electronic issue rather than mechanical issues with the refrigeration side of things.



The issue has always been with that fancy pants soft touch control panel - which obviously has an unnecessarily complicated layer of electronics behind it for a device of this type. This sort of control system seemed to be the late 80s/early 90s version of the obsession with everything having to have a touch screen these days.



As Montgomery Scott said, "The more they overcomplicate the plumbing, the easier it is to stop up the drain."

If switched on without pressing anything it should just run in fan mode - cooling or heating modes are enabled by pressing the buttons under the striped grey areas first or second from the left. Next one cycles through fan speeds, then turns on/off an ioniser, then the timer.

What it had taken to doing however was after a completely random period of time between zero seconds and about six hours is that it would drop out of cooling mode and then refuse to acknowledge any keypad presses aside from the power button or timer button (or the ioniser - but that's a completely independent subsystem which is live whenever the AC supply is on). Sometimes power cycling the unit would kick it back on into cooling mode, but not always. Day before yesterday it decided to play up once too often so I started investigating. Back right when this first started I checked out the keypad itself and ruled it out as a possible culprit. A sticking button could give similar symptoms but would also knock out the power button functionality. Plus they all checked out individually anyway. The issue was clearly with the brains of the machine.

This is the control PCB.



For something that needs to turn on/off a compressor, a heating element and switch between three fan speeds this really is unnecessarily complicated. The timer functionality is a totally separate physical unit so that's not even on this board. Likewise there's no need to run the condensate pump off the board...the switch contacts on the float are more than rated for the full load of the whole unit, so just let it handle itself and use the overflow one to cut power to everything aside from the warning light. Initial checks didn't reveal anything visibly showing signs of distress or any bulging caps. The wire you can see hanging off down by the transformer was the receiver for the remote control - I pulled that off first in the off chance something was interfering with it. Second step was to obviously pull and reseat that large socketed chip.

Here's a close up of the markings for those of you playing along at home.



Given this chip is basically running the whole show it was an obvious first port of call - sadly didn't make any difference. I also went over the board with a good magnifying glass to look for any dry joints or possibly cracked traces...Zip turned up. In fact the quality of the soldering and the traces on the board is really very good and I can't fault it at all.

Helpfully there is a simplified system schematic on the inside of the rear cover. As none of the connectors on the PCB are labelled this is appreciated.



Given the unit is thirty years old, my obvious next port of call was the DC smoothing capacitors. Looking at the voltage rails (5V and 24V) they were both slightly on the low side.



Smoothing capacitors are 1000uF 35V...and of course I didn't have any of those in stock. I did have two 470uF ones in a suitable voltage rating though so in the spirit of experimentation I tacked those on in parallel with the existing ones to see if a bit of extra capacitance would make any difference...if they'd just gone low value it probably would have gone a long way to help. Not tidy by any stretch of the imagination, but for testing purposes it'll do just fine.



It fooled me into thinking I'd fixed it as after doing this it behaved itself for about six hours...before doing exactly the same thing again.

Fair enough. My intention is basically to do away with this overcomplicated "brain" and stick a proper temperature controller in. I've got one in a box somewhere which can handle heating/cooling (this thing could only be set to one or the other - and just has a 0-9 numbered thermostat) and has proper adjustments for hysteresis, anti-cycle timers etc...I just need to figure out where the heck it is. The original PCB will stick around to handle the evaporator fan speed control, but that will basically be it. Control over the compressor, condenser fan and heating elements will be handed over to the new controller.

I wanted it back up and running today though...and I'm not one to be beaten by something like this.

The thermostat on this thing is just a mechanical make/break switch, and that quickly got me to thinking that I could very easily bypass the brain. I'd lose the anti-cycle timer, but to be honest there's a decent deadband on the thermostat I don't see that being an issue.

A little bit of poking around with a meter found that there's an always on 24V feed to all of the relay coils, and it's the earthy end that's switched by the control logic. Sure enough, if I earthed the low side of the compressor relay coil it and the condenser fan motor both kicked in, even though the unit wasn't in cooling mode.

Didn't take long for a plan to form. Even though this unit doesn't (and as far as I can see never has had) an ioniser unit fitted, the button and relay are there for it. This function being "always on" seemed to escape from the lockup issue...with the relay clicking away merrily when the button was toggled. This meant that I had an easily accessible switchable ground available to me.

That's us halfway there. I then pulled the thermostat connector off the board and spliced a couple of wires into that - wiring it in series with a wire to the switched ground I mentioned above.





Result is that the ioniser button is now a "compressor enable" button, and when that's turned on the thermostat makes it cut in/out as originally intended.

Only other thing I had to do was to physically unplug the heating element power supply as if it jumps into heating mode it will turn the element on (as in heating mode it interprets the stat being open as a cool for heat - whereas it's the other way around for cooling) because the thermostat is no longer hooked up to the PCB. Dead easy to do as it's got a socket up front.

I've not gone any further by way of making it pretty or securing the wires to the PCB with hot glue or anything as this only needs to last until I track down the proper controller, then quite a bit of re-engineering will happen. Hopefully see it going for a good while yet, and actually with better functionality as I'll be able to dial in an actual desired temperature rather than just picking a number. Plus overnight I'd really prefer the room to be a degree or two cooler than the inbuilt stat allows for...new control will resolve that. Worth noting that the wiring on there is just 24V, nothing on the mains side has been touched, and I've been careful to keep the tape from bridging the isolation gap.

Still not sure what the original problem is, and there's very little on these units on the web that I've been able to find. As best I can tell though there's something amiss with that big IC...Without another unit on hand I can rob one out of to test it's pretty hard to tell really.

It's a total bodge, but it's doing what I bought it to again, and soon will be upgraded rather than bodged.

Also in fairness to the unit...It's 30 years old and has spent a good portion of its life on an equipment rental company's books...so it's not done bad at all really! May 1991 is the date on the QC sticker on the inside of the back panel.

I used one of those little control widgets to control a fan on my Landrover Discovery transmission cooler, fitted nearly exactly where the ashtray was. Never game me a day of trouble in the time it was fitted. Handy cheap little things!

Was wandering around out back today just moving a couple of things around when my eye was drawn to something on the ground. Where has this come from?



Oh oh. That doesn't look good.



Ah balls...yep, that's going to need sorting sooner rather than later.



Temporary bodge to keep the weather out for now.



Looking around the house quite a few of the soffit boards haven't weathered this last winter well.



Worryingly it looks to me like the horizontal box section on the underside may well be asbestos...which I'm sure will multiply the costs involved in sorting things out by about ten times.



Great! Just had the first quote in this afternoon from a landscaper to sort out the back garden and driveway, and that's more than we'd hoped - by about five times. Very much hoping they just didn't want the job, but braced for the news from the one coming tomorrow to be similar. Can see this easily eating up half the budget for the garden in one hit. Either way it looks like the plans we had to improve the driveway layout will have to be canned for the time being. Which is a shame as I was really hoping we might be able to arrange things so I could get out of the garage without major car Tetris. Given the school traffic around here it basically means I often can't get out of the garage between 9 and 4 as there's nowhere to move the cars I have to shift to.

There are times I do miss renting!

After over two months thanks to problems with shipping due to Brexit related nonsense the new oil pressure switch for the Invacar arrived last week. This afternoon I figured I'd get that fitted in the hope that it cures the minor oil leak from the rear of the engine... I'm not holding my breath as I reckon it's only half the issue, the other source being the crankshaft oil seal. Which is a pain as that's an engine out job to change. If it is the crankshaft oil seal though I'm not going to lose too much sleep over it given the leakage is very slight - one or two drops when the car is parked up. If it was losing any appreciable amount while driving it would have shown up given how small the sump capacity is, but she's never used any between changes so I'm not too worried. Knowing that the pressure switch was visibly weeping though I wanted that changed. That's the sort of leak which can go from very minor to catastrophic with little or no warning.

Getting the old one out is actually deceptively awkward due to the proximity of the distributor and oil filter. Not enough to be a problem, but just enough to be moderately annoying.



Eventually managed to get a spanner onto it (24mm) with the oil filter removed. Then discovered quite how tight it was. When I started to pull the car over the wheel chocks I instead opted to remove the boss that the pressure switch is threaded into, allowing me to separate the two off the car.



That let go with an almighty crack which rammed my arm against the engine cover slam panel. This car has drawn blood surprisingly few times during the restoration project but she managed today!



Didn't actually realise I'd done that at the time, it was about ten minutes later when I had that "wait...where is this blood coming from?" moment.

Annoyingly it then quickly became apparent that my new pressure switch is completely wrong, despite having been bought from a Steyr-Puch specialist. The different case style is immaterial - however the thread and threaded length of the body are also totally different.



The length is actually important as the oil pressure relief valve spring sits against the underside of the pressure switch body so the depth it screws in is critical to the preload being right.

At least since I ordered that the actual Bosch part number (0986344041) has been tracked down so I have now got one on the way. Just annoying that I've wasted a lot of time on this - and that the £7 sensor ended up being north of thirty quid by the time shipping and all the tarriffs and fees were paid...only for it to be the wrong thing.

On a slightly lighter note though I had a nice addition that had been on my wish list for a while arrive for the calculator collection a couple of days ago. This was spotted by someone over on UKSaabs who kindly offered to collect it and post it on to me.

I'd been after one of these for a while but refused to pay the frankly ridiculous sums of money they generally seem to change hands for.





This is a HP 12C Calculator - a specialised model intended for the financial market - and a fascinating case of the "if it ain't broke, don't fix it" approach. You'd think looking at this that it's a late 70s, maybe very early 80s model, even then a really late example of a calculator that uses RPN (note the large enter key and the lack of a separate equals key).



The 12C was launched in 1981, the RPN input scheme being maintained because it's particularly well suited to financial calculations, despite the rest of the world having moved on by that point. It gets even more surprising though...you can STILL buy the 12C today, in 2021! Yes there have been numerous changes "under the hood" over the years, but the fact that a piece of electronics (even quite a specialist one) equipment has a model run of forty years and counting is frankly remarkable if you ask me.

This example appears to date from early 2001 judging from the serial number.

Quite how specialised this really is though is made most apparent by the manual.



You'd think to look at that it would be about thirty pages in English and then repeated in about 357 other languages...nope. That is all English, all 246 pages of it.

It feels like a proper quality instrument in a way that calculators just generally didn't by the time the 21st century rolled in. The keypad action in particular is lovely, you can tell that exactly the weight required to press the keys was designed in, it did not just happen because those were the switches they had in stock.

Being such an anachronistic oddball it's definitely one I'm really glad to have in the collection. Surprisingly enough it's actually the first pure RPN calculator I own! Not quite sure how it's taken me so long to get hold of one.