The job was straightforward: replace a faulty capacitor on a 24,000 BTU floor-standing unit at a factory in Ayutthaya. Khun Wichai diagnosed it in 20 minutes. He had eight different models in his toolbox — except the exact one fitted to this unit, a 50μF 450V motor-run capacitor with metric terminals. The nearest electrical supplier was 40 minutes away. By the time he returned, fitted the part, and drove back to base, a clean 90-minute job had consumed four and a half hours.

The factory paid the same invoice either way. Khun Wichai’s business absorbed the difference.

This is the hidden cost of poor van stock: not just the price of the missing part, but the labor hours, fuel, and billable opportunity lost every time a job cannot complete first time.

What Does a Repeat Site Visit Actually Cost?

Most install businesses count a repeat visit as a parts and travel line. The truer picture includes:

Lost labor revenue — a technician on a 40-minute return trip to the warehouse cannot be elsewhere. On a day planned for four jobs, one unplanned round-trip turns four slots into three.
Fuel and vehicle wear — at ฿7–8 per kilometre for a standard pickup, a 60 km return trip adds ฿420–480 to the job cost before you account for the technician’s time.
Customer friction — a customer who watches a technician arrive, diagnose, leave, and then return in the afternoon is not having a smooth service experience. Even if they say nothing, repeat visits erode trust over time.
Parts urgency premium — buying a component from a local retail supplier rather than your usual trade supplier typically adds 20–40% to the part cost.

A team of four technicians, each making one unnecessary return trip per week, loses roughly 200 labor-hours of productive capacity per year. At ฿500 per hour billed, that is ฿100,000 in avoidable lost revenue — not from poor quality or unhappy customers, but from a missing capacitor.

What Parts Cause the Most Return Trips?

The components that send technicians back are almost always the same ones: high-failure parts that come in too many variants, or consumables that run out unexpectedly mid-job.

For aircon teams:

Capacitors (motor-run and start): vary by microfarad rating, voltage, and terminal type — stock the most common sizes for the brands you service most
Drain pumps: three to five models cover most residential and light-commercial units
Thermistors and sensors: room, pipe, and coil sensors are inexpensive and lightweight; carrying a range costs little but prevents returns
Refrigerant gas (R32 and R410A): technicians should carry enough for a top-up without needing a return trip to base
Contactors and relays: fail frequently, easy to carry

For solar teams:

MC4 connectors (male and female, 4 mm and 6 mm): cheap, lightweight, and essential for any DC-side fault or panel extension
DC circuit breakers and string fuses: stock the ratings that match your installed base
Terminal blocks and cable connectors: small parts that can halt a commissioning job if missing
Cable ties and conduit fittings: no install site closes cleanly without them

For CCTV and network teams:

RJ45 connectors and a crimping tool: any on-site cable run assumes you have these
PoE injectors and splitters: a single faulty injector can ground an entire installation day
Coax and Cat6 cable lengths: carry representative lengths for your typical job sizes
BNC connectors: especially for sites with existing analog infrastructure

For fire system teams:

Detector heads (ionisation and optical): the most commonly replaced component during annual inspections
Battery types (9V and 6V lead-acid): call-point and sounder batteries fail on predictable schedules
End-of-line resistors: no zone commissioning test completes without them

How Much Van Stock Is the Right Amount?

The goal is a balance between the cost of carrying excess stock and the cost of a job-stopping gap. A practical starting point for most teams:

High-frequency consumables: 2–4 weeks of stock based on your job volume for that part. Replenish each Friday from warehouse or supplier.

Medium-frequency components (capacitors, drain pumps, detector heads): 2–4 units per van. Fail regularly but not on every job. Check and replenish after each week, not after each job.

Low-frequency but job-stopping parts: 1–2 units per van. If a missing part has caused a return trip even once in the past three months, it belongs in the van. The cost of carrying one unit is almost always less than the cost of one return trip.

Expensive or bulky equipment (replacement inverters, large cable drums): warehouse-only, ordered against confirmed job sheets before dispatch. These do not belong in everyday van stock.

Review your van stock every 90 days. Note which parts you are restocking fastest — those are candidates to increase. Parts that sit for three months without being used are candidates to pull back to the warehouse.

How Do You Know What Was Used on Each Job?

This is where most small install businesses break down. Parts get consumed, nobody records it until billing time — or not at all — and the end-of-month van stocktake is someone reading aloud while another person guesses.

A better system has three steps:

Step 1 — Pre-job checklist: Before the technician leaves the office or depot, each job generates a parts checklist based on job type (aircon PM, inverter replacement, CCTV extension, fire inspection). This documents planned consumption and prompts the technician to check their van before driving.

Step 2 — Post-job record: After the job, the technician records actual parts used — selecting from the pre-built list or adding extras. In practice this takes two to three minutes on a mobile device.

Step 3 — Attach to the work order: Parts used link to the digital work order for that job, not to a separate log or a phone call back to the office. The invoice reflects what was actually used, the job cost becomes visible, and the customer record shows what was replaced — useful when the site next needs service.

When parts usage lives in the job record rather than in memory, replenishment becomes obvious without a separate tracking sheet.

Does Recording Parts Add Too Much Work?

This is the most common objection, and it deserves a direct answer. Adding steps to a job that a technician considers already finished creates real friction.

The answer is in how you design the recording step. A pre-built checklist for each job type — aircon PM, fault call, CCTV extension, solar inverter check — means the technician is ticking or selecting from a short list, not typing freehand. Most technicians, once they see the invoice generated from their job entry rather than requiring a follow-up call from the office, adopt the habit without prompting again.

The clearest benefit to communicate early: a complete job record means the technician stops getting called back to confirm what they used or what they found on site.

Parts Usage and Job Profitability

Knowing what parts cost per job is the beginning of knowing whether a job is actually profitable.

A residential aircon PM billed at ฿800 looks healthy until you add: ฿180 in refrigerant gas, ฿120 in a drain pump, ฿60 in cable ties and fittings. The parts alone consumed 45% of the invoice value — a fact that is invisible if usage is recorded loosely or not at all. Over 50 jobs a month, systematically under-recording parts creates a gap between what the revenue report says and what the bank account shows.

FAQ

How often should we restock technician vans?

Weekly replenishment works for most teams — a Friday check against a standard van list, pulling from warehouse or ordering from your supplier. Teams with high volume or fast-moving items (refrigerant, capacitors, detector heads) benefit from a mid-week check too. The key is a standard list reviewed consistently, not an ad hoc conversation each time.

What if technicians take parts from each other’s vans?

This happens and is not a problem if recorded. When a technician takes a part from a colleague’s van, note it against the job it was used for. Without a record, both vans show stock that does not reflect reality, and shortages arrive as surprises.

Should we add a markup on parts charged to customers?

Yes. A standard markup of 15–30% above landed cost covers purchasing overhead, holding cost, and procurement admin. Apply it consistently — variable markup on the same line item is hard to explain when questioned. State the policy in your service agreement so customers are not surprised by a price above retail.

Tracking parts at the work order level — what was planned, what was actually used, what needs restocking — is the step that separates a business managing its margins from one guessing at them. OnSiteQ’s digital work orders include a parts line for every job, so usage records against the right customer and asset each time, with no separate tracking sheet required.

Spare Parts Management for Thai Install Crews