[icestrata]

I have a Dico thermostat that is currently wired for heating with propane but I my dad installed a heat strip to use instead of gas. Everything is wired and works but the heat strip heats up, then the fan comes on, then it shuts off too quickly. Do I need to have my dad wire the thermostat differently? He has not touched the thermostat yet... Thanks

[wmproop]

Are you saying he put a electric heatstrip in a propane gas furnace?

[icestrata]

He converted a propane gas pack to heat the house with a heat strip. He re-wired and installed a new heat strip. It seems like as soon as the fan turns on and cools the heat strip... the heat strip cuts off.

[hvac1000]

Actually this was not supposed to be done since it violates the listing of the appliance. Without CSA/UL approval the appliance has not been tested for safety etc.

Due to the circumstances surrounding this appliance and the fact that it has been illegally modified there is no correct answer that can be given for the problem since all would be guess work and could possibly lead to a more dangerous situation that you have right now.

My only suggestion to you is to turn off the power to the item and purchased a factory designed unit to provide the heat type you need. Sorry but over the years I have seen to many fire damaged homes on inspections where heating units have been modified somewhat like yours. It is just not safe.

Usually gas packs are outside but it can still cause major problems.

[icestrata]

The gas pack is a self contained system that sits outside the home. The heat strip in question is mounted in an unfinished basement in line with the supply ductwork. The heat strip comes on when heat is called for shortly after the fan comes on then the system shuts down. It will run in this cycle as long as it is calling for heat. The thermostat I have is for either Gas, Oil, or electric use and has switches on the back for switching between services. I don't know if it needs to be reprogrammed to work with the new heat strip or if I need to get a new thermostat. The heat strip is UL approved and installed correctly it just appears as if the controls are not working as they should.

[hvac1000]

According to your original post (He converted a propane gas pack to heat the house with a heat strip) I was led to believe he converted the propane unit to electric heat strip use.

Since this is a design build system (no manufacturer designed the system they just supplied the parts) your Dad will have to sort out the control system to make it work correctly.

Since in your words (The thermostat I have is for either Gas, Oil, or electric use and has switches on the back for switching between services.) I have no idea what you really have there and all the thermostat problems will need to be sorted out locally ON SITE not on a message board such as this.

You have way to many devices to possibly control but if your dad set the electric heat up I am sure he can figure out how to make the thermostat work properly.

NOTE: for safety
The fan should come on first
There should be a pressure switch in the electric heater that acts as a safety and does not allow the electric heat to come on until the fan volume is proven. This is the minimal safety standard that I am aware of besides the thermoal overloads built into the heater.

As far as the thermostat goes when you set it to 68 degrees it should heat to 68 degrees and then shut off. If the unit will not do that something is wrong with the thermostat or the control circuit.

[mygirlsdad77]

A question for hvac1000. I have worked on only a few electric furnaces, mosty trailer houses, and have never seen a pressure switch( at least one that looked like a gas furnace pressure switch). Can you tell me what they look like, and is there a rubber hose connected to them as on a gas unit? The electric units I have worked on, as well as the ones I have seen, always worked through sequencers. Would be helpful to know about the pressure switches if I ever have to work on another unit. And in time I'm sure I will, especially with the rising cost of propane and natural gas.

[hvac1000]

The pressure switches/interlock circuits are mandatory on strip/duct heat units only. These units come from the factory with no real way to interlock the fan for safety since the manufacturer has no way of knowing what the rest of the system may contain. This way if the fan is not moving air the electric strip heater will not come on.

Standard electric furnaces use a sequencer system that brings the fan on first before the heaters and turns the fan off last after the last heater goes off line. These are the heaters you are used to working on. This is call interlocking.


Look on page two here

http://www.tutco.com/pdfs/Accessories.pdf

And here at good old Ebay

electric duct heaters - eBay (item 290269396930 end time Oct-31-08 04:42:02 PDT)


You will see the silver air switch in on of the pictures.

UL/CSA and the National Electric Code requires some type of safety on all electric units

In the mobile home/stick built home units the safety interlock is built into the sequencers as mentioned above but in commercial or add on duct/strip heaters it is sometimes difficult to wire in a interlock so to have no doupt as to the listing of the unit the manufacturer installs a air pressure switch. That way when the unit leaves the factory it is approved as built for install and no other safety interlock is necessary. Note some commercial industrial units do not have air pressure switches but they are all required to have some form of interlock.

[KISS]

Informative, yes. Differential pressure is used to sense flow. It's basically a diaphram with a tube on both sides. The diaphram attached to a microswitch, sometimes adjustable. This is the mechanical version.

Sometimes, flow is sensed with a microswitch with a flag on top. Airflow moves the flag activating the switch. This isn't as sensitive.

[KISS]

In the "electric mode" of the tstat, the thermostat controls the fan. Exactly how remains a manufacturer's mystery.

Is it same time or delayed? Who knows?

Details. Details.