Originally Posted By: kshepard This post was automatically imported from our archived forum.
Every once n a while I run into an electronic thermostat I don’t understand. Several different HVAC contractors have told me that it’s fine to by-pass the controls at the furnace. Disconnect the white wire and hook an alligator-clip jumper between red and white lugs. They said you by-pass the circuit board this way and it’s perfectly safe.
I mentioned it at a NACHI meeting last spring, everyone seemed horrified and now I’m nervous about it. I don’t like to leave without testing the heating system.
Originally Posted By: dandersen This post was automatically imported from our archived forum.
Kent, If you must bypass the thermostat, that’s the way you do it. It is not necessary to remove the white wire from the terminal though. Just hook the jumper between the red and white.
If the unit is running in air-conditioning, some packaged gas units will not operate in heat when the air-conditioning is also running. In this case, remove the yellow wire before jumping the white.
It is always best to operate the system through the thermostat whenever possible. This ensures that the thermostat operates the equipment properly.
Originally Posted By: rfarruggia This post was automatically imported from our archived forum.
This seems to happen alot to me lately. Homeowners replace the old bi-metallic thermostats with programmable one to lower heating costs, but dont install them correctly.
I only operate the boiler/furnace through the thermostat. If that dosent work, I report "heating plant does not respond to normal operating controls. Service and repair by a qualified contractor is needed".
Originally Posted By: kshepard This post was automatically imported from our archived forum.
They told me to beware of running the air-conditioning systems using this method and I consider air-conditioning to be a less critical system (maybe not less expensive to repair or replace) so I?ve avoided testing them. I’d like to be able to do that. Have you ever had any problems resulting from jumping the controls while testing air-condition systems?
If you are by-passing the thermostat to start the heating system, how do you know that the system is functioning normally?
James
I don?t, but I know a lot more than I would if I just walked away.
Homeowners replace the old bi-metallic thermostats with programmable one to lower heating costs, but don?t install them correctly.
Ranymond
This must mean that when you attempt to operate the thermostat, the system doesn?t respond to the controls, so you have no choice but to jump it in order to test the rest of the system? When it doesn?t respond, do you then check to see whether the thermostat is installed incorrectly? Do you follow some sort of diagnostic procedure?
Originally Posted By: dedwards This post was automatically imported from our archived forum.
I do not by-pass any normal operating controls. If I have to by pass normal controls then the unit regardless of what it is requires the services of a qualified and licensed professional. When you by-pass the normal controls you just made yourself responsible for anything that may go wrong with it whether you caused it or not. The last thing the client or seller will remember is that YOU did something out of the ordinary. You basically just performed “troubleshooting” techniques on the piece of equipement. I have a statement that says “Could not inspect, did not respond to normal operating controls”
I am certified in HVAC and I do not do it because it is outside the scope and usually the training of the HI. Your call, but I do not recommend it.
Originally Posted By: dedwards This post was automatically imported from our archived forum.
Another thing to consider. Most modern equipment, not just HVAC, has safety features built in to preclude people and equipmetn from injury and damage. Most safety devices disable the unit from working. If you decide to “override” operating controls, you may well be overriding safety devices installed by the manufacturer to preveat the the operation of the equipment and now open yourself for all kinds of unpleasant consequences. I take the time to explain this to the client. I find loose flue pipes often. Do I just reconnect them and perform the furnace check?..HELL no! I write it up, tell the customer AND the seller they will need a service tech to reconnect and perform any necessary safety checks and while they are at it perform a functional / capacity check. If you “fix” something while doing the inspection you are open for anything that could go wrong as a result. I am asked all the time if I couldn’t just reconnect it or fix this while I was there. I remind them I am an inspector, not their serviceman.
Originally Posted By: jrupert This post was automatically imported from our archived forum.
If you by pass the thermostat and short out the transformer you will pay for the repairs, most furnaces today do not make it easy to do with out removing the control cover or undoing wire nuts, and it is out of the scope of the inspection
John Rupert
Accurate Property Inspections
Solitaire Heating & Cooling
CSG Training (HVAC Training & Consulting)
Originally Posted By: rcooke This post was automatically imported from our archived forum.
jrupert wrote:
If you by pass the thermostat and short out the transformer you will pay for the repairs, most furnaces today do not make it easy to do with out removing the control cover or undoing wire nuts, and it is out of the scope of the inspection
John Rupert
Accurate Property Inspections
Solitaire Heating & Cooling
CSG Training (HVAC Training & Consulting)
I was told by a gas man not to by pass the thermostat as you can burn out the anticipator in the thermostat . This is what shuts the furnace of before it get up to temp in the home with this not operating properly you get a home that is to cool when the furnace comes on then it is too hot when the furnace finishes it's cycle.
Originally Posted By: jrupert This post was automatically imported from our archived forum.
The heat anticipator can not be shorted by bypassing the thermostat. This can only be done if the 24volt control is grounded allowing a large amp draw through the thermostat, such as shorting between the gas valve connections or touching the white wire to the case of the furnace
You are correct on the function of the anticipator , when set properly it will turn the furnace off slightly before the house reaches the set temp, preventing over heating. A thermostat that has a ?open? or ?shorted? anticipator will not function in the heating mode
John Rupert
Accurate Property Inspections
Solitaire Heating & Cooling
CSG Training (HVAC Training & Consulting)