HVAC hacking

Yup. At my old house (1969-1994), I had such a natural gas furnace, except everything was bimetal strips and relays. So, over that 25 year period I had to rebuild the blower motor a couple of times, and replace: (1) thermal safety on gas ignition, (2) fan normal "run" bimetal and (3) bonnet over-temperature bimetal. ...Jim Thompson

cro.

It's possible that the temp. limit switch had been replaced (currently at 180F), since there is a service sticker on the unit. However, the smaller unit still has a limit switch of 250F, which could be the original. There were some fire recall issues years ago, but i don't know the details. I'll check around with the neighbours, since we all have the same type installed when the houses were built. If possible, we should probably all change to around 200F.

The old mechanical thermostats had an "anticipator", the adjustable ones had a bit of resistance wire and a wiper arm often calibrated in amps. Basically a potentiometer with one end of the element open. The calibration was referring to the current draw of the relay or gas valve in the furnace. The idea is that when the thermostat contact closes to call for heat, the resistance element heats up and causes the thermostat contacts to open earlier than they would have without a nearby source of heat. These could be adjusted to get the right amount of run time on the furnace.

First, you ought to use a meter to see what the actual on time of the thermostat is. If it is calling for heat in very short cycles, there may be a way to adjust it to have less anticipation.

It may be with such a short cycle that your ducts, heat exchanger, etc. never get up to full temperature, and that's why it blows cold air at the end of the cycle.

It may also be the heat exchanger thermostat is set too low, keeping the blower on when the heat exchanger has already gotten quite cool.

Putting a thermometer in the air duct might indicate how hot and cool the air is getting.

Jon

Really suggest you get the manufacturer's installation / service guide for your model. Look for any bulletins to bring it up to current standards. The original schematic should be on the door to the blower compartment.

he

Yes, the label says "Maximum outlet temperature of 200F", but the cutoff switch is 250F.

Do you have good solid blower-driven airflow? That's the usual reason for short-cycling.

Another is a bad t-stat. Mechanical ones use a resistor "anticipator" to avoid overshoot. If the valve draws more current than it's set for...

It's a combination of bad t-stat and air vents. Too much hot air near the t-stat. So, we changed to a d-t-stat and blocked some air vents with filters. Also, we added new fans to redirect air flows. Right now, it's manual on/off. Yes, that means me. What i want is to tie the two new fans to the main t-stat, since we want to draw air to the living room during the day, bedroom during the evening, and off at night.

Somewhere, in my surfing for ways to cool my office, I ran across registers that had fans in them. ...Jim Thompson

s:

..

Yes, i was thinking the same. We need to push (near the furnace) or pull (at registers) more air based on main settings. But i need a way to talk to each fan independently. My wife would not allow wires all over, so probably bluetooth or zigbee wireless.

There is wire rated for use in duct-work (I think it's called plenum cable). I used a son's battery powered toy car to pull wire in the duct-work at our old house ;-) ...Jim Thompson

ites:

r"

or...

That will probably work for the first level. But we have two levels independently HVAC. We don't use the second level heater, because it would be burning oxygen in the room. The first level burns in the garage. There are no ducts between the levels. The house was built for look, not practicality.

WHAT? That doesn't sound legal. There should be ducting from the outside air to support the burner chamber's oxygen needs, plus a flue for exhaust gases.

And gets its oxygen where? Better be from outside air plus have an exhaust flue, or it's not to code.

No closets where you can play duct-man between levels ?:-) ...Jim Thompson

You can use the ductwork itself to "fish" a thin string through, then use that to pull a heavier string, then use that to pull your wires and run them 'inside' the HVAC.

This is, of course, only suggested for signal lines or fused LVDC runs. Do not make AC wire runs 'inside' your HVAC system.

So, for your wireless, you need a mass airflow sensor, and a wireless data link to send the figures to your PC. Seems like this would be cheaper these days.

I did a 40' horizontal fish last month for a friend and it took me several hours (fishing isn't easy working alone). Horizontal runs are a major pain, and he had foam sprayed everywhere as well (wintry zone).

Wireless is here to stay. We just have to make it more secure at the individual item level. As each unique handshake takes place in a system, other intrusions should be locked out.

Keep a close eye on your transactions on your cards too, folks. There are e-thieves all over the place out here.

on

ll

ator"

t for...

ear

the

Noop. Nowhere to draw in outside air for burning, but there are exhaust vents.

Wait until i tell my wife: Honey, we need to open the kitchen ceiling for duct works.

for...

Jeez... it is just a little friggin drywall.

Smack da bitch (with the logistics, of course).

The thin string and the fluttery "kite" on the end of it will work to get started with fish lines. Block all the vents except where you want the fish to go.

for...

Is this an ancient house or relatively new? If relatively new, or FHA certified, sue everyone in sight.

At the old house I raised the floors of two adjacent closets by 9" to bring duct work from outside to the furnace closet, where I could make a slide-controlled connection to the house ductwork. Then added a ground-mounted evaporative cooler (6000CFM... equivalent to 13 Tons of A/C :-) ...Jim Thompson

ction

will

cipator"

set for...

r near

ents

ght

tie

to the

at

way

ll

Yes, she is a picky b* (hope she is not reading this). I can fix anything but drywall. She end up paying $1000 for a professional fixer to fix my fixes. She still complaints about the work, but she hired the professional, not me.

ction

will

cipator"

set for...

r near

ents

ght

tie

to the

at

way

ll

it

Around 25 years old. They already did. The previous owners and HOA (around 300 houses) sued and bankrupted the builder, on other unrelated issues. But i heard that the builder is still around building, just born again financially. When i get to it, i would sue the city planners and inspectors.

Run 'Plenum cable' inside the ductwork.