The best HVAC Technicians I have been around have one thing in common, a systematized approach to system diagnostics. They have a procedure that they follow each and every time.
This past week, I was out with a service tech. We went to a call that had the same intermittent problem and three service calls where the problem could not be identified or fixed.
The system is a residential gas package unit. A gas package unit is one piece of equipment that has a gas furnace and an air conditioning system combined.
The Customer’s Description of The Problem
When the customer called in, they described that the system (in the heating mode) started up and then shut down almost immediately. Then after three attempts at starting, it shut off completely. They were quite frustrated at the HVAC company’s inability to identify and fix the problem, and rightly so.
Notes From the Three Previous Visits
Technician #1 – “Arrived at the call and found the error code indicating a flame roll-out switch error. I reset the flame roll-out switch and observed the system operation. System started up in the heating mode and is operating properly at this time.”
Technician #2 (two weeks later) – “Found the system with error code, 1 slow blink and 5 fast blinks. This is the error code for a tripped roll-out switch. I reset the roll-out switch and checked temperature rise. The temperature rise was a bit high but within acceptable limits. Observed the system through on complete heating cycle. The unit is operating properly.”
Technician #3 (one week later) – “The system was tripped on a roll-out switch error. Reset the roll-out switch and the unit started up in the heating mode. I check the gas pressure and everything is working fine. We may want to speed up the fan speed if this continues to happen.”
Now, keep in mind each technician is sent, and can read, the notes from all previous visits. They immediately assumed, and jumped to conclusions on their diagnostics.
A Quick Note on Roll-out Switches
Above is a picture of a flame roll-out switch. It is positioned very close to the burner compartment of a gas furnace. (You can see the two dark holes in the picture, that is where the flames shoot in.) The roll-out switch is a thermal protection safety device that, if there is a flame problem, where the flames are present where they do not belong, it will trip, shutting off the furnace. The red button between the wires must be pushed to reset the flame roll-out switch.
A tripped flame roll-out switch is an indicator of a very serious problem. An INDICATOR, NOT THE PROBLEM.
Now, back to the fourth technician.
Service Call Number Four
Technician #4 read all of the previous notes and knows that it is probably going to be a flame roll-out error. What would you expect him to do? Here is what I expected him to do:
- Look at the error code
- Immediately reset the roll-out switch
- Check the gas pressure
- Observe the system operation
- See that is was working properly and leave
To my surprise, here is what he did: (pay attention, this is the systematic diagnostics for every HVAC electrical problem.)
- He talked to the customer
- Went to the thermostat to call for heat
- Went back out side to observe the system operation
- Found that the heating was not working
- Removed the service panel from the unit
- Using his voltmeter, checked to make sure there was incoming line power (230 volts)… and there was.
- Using his voltmeter, checked to make sure there was control voltage from the transformer (24 volts)… and there was.
- Disabled power to the unit.
- Visually and physically inspected the wiring, starting with the line voltage wiring. Checking for broken, loose, or corroded connections… he found that the line voltage wiring was good.
- He did the same with the control voltage wiring.
Below is what he found.
A broken connection on the white wire, which was probably not the primary issue, but would have caused another no heating service call in the future. (The blue wire is what it should have looked like).
NOTE – He DID NOT go directly to the flame roll-out switch or the error code.
Next he continued on with his systematic troubleshooting inspecting the remainder of the control voltage wiring. Here is what else he found.
A corroded and broken wiring connector on the flame roll-out switch AND the roll-out switch was not tripped.
The previous technician probably pushed the reset button which jiggled the broken connection so it made contact and that is why the furnace worked.
Three trips, three technicians, and this simple and obvious issue wasn’t identified! Totally unacceptable.
What did we learn about HVAC Troubleshooting?
- Go to the thermostat, call for heating or cooling and see if the system works and what is happening.
- Check for incoming line voltage. Nothing happens without it.
- Check for control voltage. Nothing happens without this either.
- Check the line voltage wiring for looseness, corrosion, or breaks.
- Check the control wiring for looseness, corrosion, or breaks.
- Never assume what the problem is. Either from error codes or previous technicians’ notes and observations.
Please be like Technician #4
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