Second Opinion: Prior PM Suspected, Validate vs Redo Decision Tree

Why this matters

A customer calls and says the last service company did the PM, but the system is faulting and they suspect the work was done poorly or not at all. You arrive to validate the prior PM or to do whatever the PM should have done. The wrong move is to either rubber-stamp the prior work or to redo every line item. The right move is to validate the items most likely to be the cause of the current fault, then decide whether a broader redo is necessary.

This is a defensible scope-of-work problem. ASHRAE, ACCA, and the PHCC service standards all describe how a PM checklist should be documented; this decision tree gives you a way to validate against those standards without spending the customer's time and money on items that are not at issue.

Symptom presentation

• Customer reports recent PM and current fault, asks for a second opinion
• Equipment is faulting in a way the PM should have caught (filter not changed and airflow now blocked; cap not gasketed and now leaking; refrigerant not weighed and now short)
• PM sticker on the equipment, but conditions suggest checklist items were not done
• Documentation shows extensive PM, equipment condition contradicts the documentation
• Customer is preparing to terminate the relationship with the prior provider and wants validation

You are not necessarily there to indict the prior contractor. You are there to find out what is true.

Quick checks

1. Ask the customer for the prior PM documentation: invoice, checklist, technician notes. The level of detail tells you what they say was done.
2. Walk the equipment. Look for physical evidence consistent with each checklist item.
3. Identify which PM line items would be visible after a few weeks: filter condition, coil cleanliness, belt tension, lubrication state, drain pan cleanliness, anode condition, brush wear. These tell you whether the PM was performed.
4. Identify which PM line items relate to the current fault. Focus your validation there.
5. Note any items that are date-stamped or signature-recorded (refrigerant weigh, combustion analysis, electrical insulation test). These should have specific values that you can re-measure.

Validate vs redo tree

Branch A: Validate only

Take this branch if all of the following:

• The current fault is a single failed component, not a pattern
• The visible PM items appear to have been done (filter is new, coil is clean, belts are correct)
• The customer wants a specific question answered (did the PM cover X?) rather than a wholesale redo
• The prior PM was recent enough that you can re-measure the same parameters and compare

Your work product is a written validation: this is what the prior PM documentation claims, this is what I measured, this is what I found, here is the verdict. Validation does not require redoing the PM. It does require enough measurement to confirm or contradict the documentation.

Branch B: Redo the items related to the current fault

Take this branch if:

• The current fault traces to an item the prior PM should have addressed but did not (clogged filter that PM claims was changed; refrigerant short that PM claims was charged)
• The visible evidence on those specific items contradicts the documentation
• The customer wants service that addresses the current fault and incidentally validates the PM

You redo only the items in scope of the current fault, with documentation showing what you found and what you did. The customer sees both: the corrective work and the validation outcome.

Branch C: Full PM redo

Take this branch only if:

• The visible evidence shows multiple PM items were not done (filter looks original, coil is filthy, belts are slack, drain pan has standing water)
• The customer authorizes a full PM after seeing your initial findings
• You can complete a full PM in the visit window or schedule it separately

A full PM redo is a separate scope from the original call. Quote it explicitly and proceed only with authorization.

Branch D: Full diagnostic, no PM redo

Take this branch if:

• The current fault is unrelated to anything the PM would have caught
• The PM appears to have been performed at a reasonable level
• The fault is independent (component failure, environmental change, customer-induced condition)

Diagnose the current fault on its merits. The PM is not the issue.

Confirming the assessment

When you reach a conclusion, anchor it to measurements, not opinion. "Capacitor reads 28 microfarads on a 45 microfarad nameplate, PM documentation from 30 days ago shows no capacitor reading recorded" is a defensible finding. "The other guys didn't do their job" is not.

Stay neutral about the prior contractor. Your job is what you found, not what they did or did not do. The customer can draw their own conclusion from the facts.

Next steps

Document the visit clearly: scope, what you measured, what you found, what you did, what the verdict was. If you have validated that the PM was done correctly and the current fault is independent, the customer's complaint against the prior contractor is resolved on the facts. If you have found that the PM was not done as documented, the customer has the basis they need.

Set expectations for ongoing service. If the customer is switching to your company, propose a PM scope that you can deliver and document so the next second-opinion visit on this equipment finds defensible records.

References

• ACCA Standard 4 Maintenance of Residential HVAC Systems, PM checklist scope and documentation
• ASHRAE Standard 180 Standard Practice for Inspection and Maintenance of Commercial HVAC Systems
• ISO 13379-1 Condition monitoring and diagnostics of machines
• ISO 14224 Reliability and maintenance data collection, documentation requirements
• PHCC National Standard Plumbing Code, service-and-maintenance documentation guidance
• NFPA 70B Recommended Practice for Electrical Equipment Maintenance, documentation