PM Frequency Decision for Rooftop Units With a History of Coil Fouling
A retail portfolio has 40 rooftop units, all 15 years old, serving sales floors. Filter changes are on a quarterly PM schedule, but the maintenance log shows 11 compressor failures in three years, all on units serving the loading-dock side of the stores. Coil cleaning was last documented two years ago. The current PM contract prices quarterly filter changes at $85 per unit and semi-annual coil cleaning at $420 per unit. A compressor replacement averages $6,500 installed. The portfolio manager asks whether to increase PM frequency or accept the failures as end-of-life. You have one year of trend data showing discharge pressures on the dock-side units running 30-40 psi above the other units.
1. Analyze the economics and the failure pattern to recommend a PM frequency and scope change.
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Failure pattern. All 11 failures are on dock-side units, and those units run 30-40 psi above the rest on discharge pressure. That is a strong signal of condenser fouling or restricted airflow, not random end-of-life. Dock-side units see more lint, dust, and exhaust, so filters load faster than a quarterly schedule assumes.
Economics. Current quarterly filter PM is 40 units x 4 visits x $85 = $13,600 per year. Semi-annual coil cleaning is 40 x 2 x $420 = $33,600 per year. Compressor replacements at 11 over three years average about 3.7 per year x $6,500 = roughly $23,800 per year, plus downtime and lost sales.
Options.
- Increase filter changes on dock-side units to monthly or bi-monthly. Cost: roughly 12 dock-side units x 8 extra visits x $85 = about $8,200 per year, far less than one compressor.
- Add annual coil cleaning on dock-side units and keep semi-annual on the rest.
- Add a discharge-pressure trend check to every PM visit so fouling is caught before it damages compressors.
Recommendation. Do not accept the failures as end-of-life. Move dock-side units to monthly filter changes and annual coil cleaning, keep the rest on the current schedule, and add pressure trending. The incremental cost is a fraction of the avoided compressor replacements.
2. How would you structure the PM contract change and what performance measures would you use to confirm the change is working?
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Contract structure. Split the portfolio into two service tiers: dock-side units (higher frequency, coil cleaning included) and standard units (current schedule). Price the tiers separately so the cost difference is visible. Require the contractor to record filter loading, coil condition, and discharge pressure at each visit in a shared log.
Performance measures.
- Average discharge pressure on dock-side units versus standard units, tracked monthly; the goal is to close the 30-40 psi gap.
- Number of compressor failures per year, with a target of zero on dock-side units.
- Filter change compliance rate and coil-cleaning completion rate.
- Callback rate and average time to resolve comfort complaints.
Review cadence. Review the measures quarterly for the first year and adjust frequency if the pressure gap closes. Build in a mid-year review so the schedule can be tuned rather than locked for the full term. Document the baseline now so the comparison is credible.