We still have a couple of the Saab 9000 belt tensioners left if anyone is still spannering on these great cars.  Looks like I’ll be needing one soon as my son’s 1997 9K is dribbling coolant slowly from what appears to be the water pump.  Will get in there this weekend and have a look while it’s up in the air for its oil change.

On the hydronic heating front capitalism triumphs again- eco blocks have come down in price to the point where they are now competitive with cord wood so we’ll be acquiring up to 10 tons of these over the coming summer as we switch from wood to compressed blocks in the Econoburn boiler.  See the Hydronic Heating category.  Our boiler is connected to a masonry chimney so we have to keep that thing clean so the creosote doesn’t light off.  Currently I have to get it cleaned 3 times a season.  Hopefully with the blocks I can get that down to once per season.  Also this year we need to get a backup heating system installed.  Will probably go with propane since geothermal installation costs are so high, and electric is so expensive, that the capital costs will never be recovered.  Oh well, maybe some day we’ll finally get gas out this way…

Recirculation motor with broken actuating arm

The repair or replacement of this item is fairly easy, as repairs to Saab 9^5 HVAC systems go.  Here is a quick outline of what has to be done:

• Remove passenger (LHD cars) footwell cover from left wall;
• Remove under dash cover;
• Remove glove compartment;
• Remove recirculation motor (broken arm usually drops out when motor is removed);
• Repair motor;
• Replace motor and reassemble everything in reverse order.

For early (pre-2001) 9^5′s it’s possible that the motor could be non-operative due to a burned out resistor.  If your ACC calibration failed with a code 21 this indicates a failed recirculator motor.  Replacement may be your only option on the later cars as mine (MY2001) has the motor sonic welded together, there’s no practical way to disassemble it to replace the failed 18 ohm resistor that tends to happen on the early cars.  It’s easy enough to test the motor on the bench with a 12V power supply.  Apply voltage one way, then reverse the polarity to move the motor back in the other direction.  You will need to do this in any case in order to move the shaft to a middle position if you effect the repair I listed below.  A replacement actuator arm part (part number 4869426) can be found at www.gmpartsdepartment.com for about $USD20 last time I checked.  Since this didn’t look like too much trouble to frig a repair, and the force needed to move the recirculation flap is pretty small, I decided to try a fix.

Detailed Repair Instructions

Remove passenger side footwell cover by removing 3 plastic anchor pins:

Passenger Footwell Cover for HVAC

WARNING: don’t try to forcefully pull out the 3 clips!  They come out really easy if you know the secret: use a small screwdriver and push in the center pin about 1/8″.  It should click and stop.  At that point the clip is released and should just pull right out.  For reassembly, push the center pin out from the inside of the clip.  Insert the clip and pin back into its hole, and depress the center pin flush in order to lock in the clip.  (Sure wish we had these on the Saab 9000!)  Remove the cover, and note the locating pin behind the upper plastic clip.

Remove under dash cover by removing 4 T25 screws as shown below:

Passenger side under dash panel mounting screws

Remove the glove compartment by removing 3 screws at the bottom:

Glove compartment lower mounting screws

Then remove the three screws behind the door at the top:

Glove compartment upper mounting screws

Gently pull the glove compartment forward, and disconnect the two leads for the glove compartment light and the small hose for the cooling air.  Remove the glove compartment from the car, and now you should have full access to the right side of the air box.

Air Diverter and Recirculation Actuator Motors

Disconnect the electrical connector for the recirculation motor, and remove the connector from the bracket.  Remove the two 6mm/Philips screws holding the motor in (the left screw is deep inside the boss shown, use a #2 Philips on this one) and remove the motor.  Replace the broken actuator arm and reassemble.  Or, if you are cheap like me, repair the arm and then reassemble.

I made up a little piece of 0.025″ thick aluminum and epoxied it to the motor and broken shaft:

Arm Reinforcement Piece

Repaired Recirculation Motor

I used a clear epoxy. JB Weld would probably work as well.  Shim the broken arm in place until the epoxy sets, then remove the bits while you still can to keep the epoxy from creating a mess by sticking to the shims, then be patient and let the epoxy fully harden.  To ease reassembly, use the power supply to run the shaft to its full CCW position (this is the default position of the recirculator flap).

Have fun!

Saab 9000 belt tensioner compression tool

I have a few of these made up and enough material on hand for a few more. If you are interested in obtaining one ($20USD incl. shipping in USA) please send a message to the administrator at jeffs@fairwayacademy.org.

Update, June 2011:  I have been able to fulfill all backorders and have a couple extra tools left over for immediate shipment if anyone is interested in obtaining one of these tools.

We’ll continue to chronicle life with wood heating, as we are most of the way (hopefully…) through our second winter of relying exclusively on our EconoBurn EBW-100 boiler for heating and domestic hot water.  Sorry about the confusion, hopefully Google will have things all sorted out once it deals with my sitemap.xml file.

Yeah, and I also apologize for the dweeby default WordPress theme, but I’ve just spent the last two weeks hacking on php and css for the FOM Systems site and I’m just not in the mood at the moment for something more fancy, sorry.

-Jeff

I can’t emphasize enough the importance of maintaining the proper pH level of the water in the system, since this is responsible for ensuring long system life and minimizing any corrosion problems.  Many hydronic systems are severely neglected regarding this.  A friend of mine who installs geothermal systems reports that since he started raising the pH of the water in the ground loops and heating loops of the systems he installs this has virtually eliminated problems with rust and corrosion.

-Jeff

Another stumbling block was sleep/wake. Since the 16F883 is code compatible with other parts in this series such as the 16F685, and the data sheet listed the same example code as for the 16F685, we had to struggle a bit with the 16F883 when it refused to wake up after entering sleep mode.  We never did get a satisfactory answer back from the Microchip forum about this so are publishing this here for your enjoyment and perusal.  Here is the sleep entry code for the 16F883, our first attempt:

MAIN_sleep_entry
	BANKSEL	PORTA
	clrf	PORTA
	BANKSEL TRISC
	clrf	TRISC	    ;all to outputs
	movlw	H'20'	    ;only enable bit 5
	movwf	IOCB
	bcf	PIE1,TMR1IE ;stop timer 1 ints while here in this bank...
	bcf	PIR1,TMR1IF ;case we come here from interrupt routine...
	bcf	INTCON,T0IE ;make sure timer 0 can't hit us either...
	BANKSEL	T2CON
	bcf	T2CON,TMR2ON ;stop timer
	BANKSEL PORTA
	clrf	PORTC
	clrf	PORTB
	movf	PORTB,W	    ;dummy read to clear state change ff's
	movf	PORTB,W		;again for good measure...
	bcf	INTCON,RBIF
	bsf	INTCON,RBIE ;arm wake up detection
	bsf	INTCON,GIE
	clrwdt
	BANKSEL WDTCON
	bcf	WDTCON,SWDTEN
	bcf	INTCON,T0IF
	bcf	INTCON,INTF
	bcf	INTCON,RBIF
	nop
	sleep

This is the same code sequence previously used for the 16F685, but for some reason the 16F883 would never wake up.  After trying several things, without success, we added this code right before sleep entry:

	.....
        bcf	INTCON,RBIF
	btfsc	INTCON,RBIF
	goto	$2
	nop
	sleep

Since we still went to sleep, obviously the RBIF flag was getting cleared, later verified by stepping through with the ICD2 debugger.  But it still looked for all the world like the RBIF flag was still setting prior to sleep entry.  So we tried another hack.  At the dispatcher at the top of the interrupt service routine we added a handler for the wake interrupt:

	...
	btfsc	INTCON,RBIF
	goto	SLEEP_WAKE
	goto	IRQ_DONE	;wild interrupts are ignored

SLEEP_WAKE
	bcf	INTCON,RBIF	;this might be causing problems
	goto	IRQ_DONE	;

Sure enough, after handling the RBIF flag inside interrupt context, the wakeup circuitry was armed and we could now wake the 16F883.  So what’s going on here?  The RBIF flag can obviously be cleared from normal context but it won’t stay  cleared unless it’s cleared inside interrupt context.  This isn’t the way the 16F685 behaves and sounds like we have the makings of a nice little hardware bug here.  Comments?

I found with the QT1081 chip that key presses were very reliable, with no issues with double hits, etc., that one might encounter with a mylar keypad.  The sensitivity of each key pad is easily adjusted to compensate for the differing amounts of stray capacitance associated with each key pad.  Best of all, the power consumption is very low.  A system using a PIC16F883 processor running at 4MHz with the QT1081 detecting a single key consumes only 2.4mA from a 3.0V supply.  An overview of the operation of digital capacitive touch technology can be found here.

Adjusting QT1081 key touch sensitivity

A datasheet for the QT1081 may be found here.  Please download this and turn to page 6, as figure 1.1 contains a reference schematic which will be used for the remainder of this discussion.  The values shown for the resistors and capacitors connected to the SNS** pins are good starting values.  The 1M resistors that are used to set the AT1081 operating modes will affect the sensitivity of their respective key inputs.  I discovered that SNS pins that were pulled to ground were less affected than SNS pins that were pulled off to VDD.  The values for CS0 through CS7 are MINIMUM values it seems.  I found that with the CS* capacitors set to 1000pF (1nF), keys with option resistors pulled off to VDD would not reliably detect a touch.  However, increasing CS slightly for those inputs to 2000pF resulted in working keys.  The datasheet claims that capacitors as large as 50nF (0.05μF) can be used for sensing capacitors.  Power consumption increases as larger values are used for CS.  Use no more capacitance for CS than necessary to achieve reliable operation.  Capacitor selection is discussed in section 3.3, page 11, of the datasheet.

Capacitive touch opens up many new design possibilites.  Other touch controllers in Quantum’s product line include slider bar and wheel sensors with up to 256 discrete positions that can be sensed.  Elimination of mechanical switches can be a huge win in terms of product styling and reliability, as well as cost reduction.  Because the Quantum components use a digital algorithm they are able to adapt to long term changes in the capacitance of the button array, such as water droplets on the sensing surface.  This reduces issues with “stuck” keys.

“Those studios with vast libraries of analog master tapes may find little or no use for them when the world “goes digital” in a few years. But as for the fears about the obsolescence of the conventional vinyl disc, I think that such fears are over-exaggerated. The digital disk will make its way into homes slowly, I feel, and the analog LP discs which have been sold by the billions are not about to be discarded overnight, or even over a span of ten or more years. I’m not saying that they will never become collectors’ items— only that it’s a bit early to discard our collections of 12-inch LPs before we see which way the digital disk is really going to go— and how soon it’s going to get there.”

Hahahaha! This is one reason I love history, it’s so much fun looking back to see how things really turned out, and how often the experts get the future wrong. To be sure, it took a while for CD’s to make it to our shores (I didn’t purchase my first CD player until 1985, a Sony CDP-302, which is still in service by the way) but by 1986 vinyl disappeared virtually overnight from the stores. I think Len Feldman completely overlooked the convenience factor of CD’s. On good equipment vinyl sounds almost as good as a CD, and certainly a poorly recorded CD will sound worse than a good vinyl recording, but to be free of the hassle of handling LP’s and constant fiddling with turntables and styli, the cleaning, need to turn them over after 20 minutes or so, and the wear out issue, the same things that drove many to use cassettes to record their record collections when cassettes’ quality got good enough, was the big driver in the rapid embrace of CD’s. It’s hard to believe CD’s have been with us for almost 30 years. Which is why the current struggle of Blu-ray against ordinary DVD’s may not turn out the way futurists predict today. While the conventional DVD was a vast improvement over the VHS tape, many people can barely tell the difference between an upscaled DVD and a Blu-ray video image due to the long history in this country of people accustomed to watching sub-par video. Blu-ray is no more or less convenient than DVD, so from that perspective there is no reason at all to upgrade to Blu-ray. Even many folks with HD tv’s often can’t tell if what they are watching is in high definition or not! We’ve been down this road before, folks. When was the last time you purchased a superAudio CD? I thought so…

Heat transfer calculations in hydronic systems are dead easy, so there’s no excuse for not running the numbers. In the USA we still use BTU for our units for heat. Recall that 1 BTU is equal to the amount of heat that causes a temperature rise of 1^oF of 1 pound of water. Let’s say we have something like a geothermal system that uses a ground loop. A fluid, usually water or water mixed with glycol to prevent freezing, is circulated through the ground loop outside and a heat exchanger inside, either transferring heat from the refrigerant circuit (summer cooling) or transferring heat from the ground to the refrigerant circuit (winter heating).

1. A geothermal system is operating at steady state in cooling mode. If the flow rate in the ground loop is equal to 10 gallons per minute, the temperature of the water entering the loop from the heat exchanger is 110^oF and the water returning from the ground loop is 90^oF, what is the amount of heat, in BTU per hour, that is being conducted into the ground?

Answer:

heat transfer(BTU) = ΔT * Flow rate(gpm) * 8.3 * 60, where ΔT is the temperature drop around the ground loop in degrees F from input to output.

We simply multiply ΔT times the flow rate times weight of 1 gallon of water times 60 minutes. We have to multiply by 60 to rationalize our units since flow is in gpm but we want to know the number of BTU’s per hour. Since 8.3 * 60 = 498 it’s common to write the heat transfer equation simply as ΔT times flow times 500, to make it easier to do ‘rule of thumb’ calculations in one’s head. So the answer to our question is then:

20 * 10 * 500 = 100,000 BTU per hour.

So remember, it’s simply delta T times flow times 500. Not so hard, is it?