A Magna customer called us at 2:15 PM on a Friday in late July, reporting that their AC had stopped cooling effectively earlier that day. By the time they called, outdoor temperature was 97°F, indoor temperature had risen to 84°F despite the AC running continuously, and the customer noticed water dripping from the indoor air handler. They had a family gathering scheduled for that evening and needed cooling restored before guests arrived.
This case study documents a same-day emergency AC repair where the diagnostic identified a relatively simple underlying cause that produced significant symptoms — a useful example of how proper diagnosis prevents unnecessary equipment work.
Customer Situation
- Home: 2010-built Magna two-story, approximately 2,100 sq ft
- Existing equipment: 14-year-old Lennox R-410A AC, 3.5 ton; matching 96% AFUE furnace as air handler
- Symptom: AC running but indoor temperature rising; water dripping from indoor air handler; ice visible on refrigerant line at outdoor unit
- Severity: Family gathering scheduled for evening; 97°F outdoor temperature; indoor temperature 84°F and rising
- Time of call: 2:15 PM Friday afternoon
Initial Phone Triage
Dispatcher gathered information:
- AC running constantly: yes
- Air coming from registers: yes, but customer described as “barely cool”
- Water dripping: from indoor unit area
- Ice visible: customer reported visible frost on copper line at outdoor unit
- Last filter change: customer couldn’t recall — “probably a while ago”
Likely diagnosis from phone information: Frozen evaporator coil, almost certainly caused by restricted airflow (dirty filter)
Guidance to customer:
– Turn off cooling mode immediately (continued operation makes ice problem worse)
– Turn fan to “ON” position (without cool) to thaw coil before our arrival
– Place towels around indoor unit to manage thaw water
– Estimated arrival: 90 minutes (3:45 PM)
On-Site Diagnostic
Arrival: 3:38 PM (under estimated time)
Technician: Jordan Whitmer (lead technician)
On arrival observations:
– Outdoor unit running but ice still visible on refrigerant lines
– Indoor unit producing thaw water (~1 gallon collected)
– Air filter: 1″ pleated filter, completely clogged with dust and debris
– Estimated filter age: 6+ months based on dust accumulation
Customer interview:
– Filter last changed: customer remembered changing it “around Christmas” → 7 months prior
– No other recent system changes
– AC had been working fine until “earlier this week” when cooling started getting less effective
– Indoor temperature drift had been gradual until today
Measurements after coil fully thawed (45 minutes of fan-only operation):
- Existing filter: removed and measured static pressure across it — 0.38″ wc (severe restriction, typical clean filter ~0.05″ wc)
- Replaced filter with new pleated filter
- Static pressure with new filter: 0.06″ wc (normal)
- Outdoor temperature: 96°F
- Indoor temperature: 86°F (initial after restart)
- Suction pressure: 136 psi ✓
- Discharge pressure: 348 psi ✓
- Subcool: 9°F ✓
- Compressor amp draw: 14.2 amps (nameplate 15) ✓
- Temperature differential across coil after stabilization: 19°F ✓
- Refrigerant charge: properly charged (verified by subcool method)
Diagnosis confirmed:
Frozen evaporator coil caused by severe airflow restriction from dirty filter. No equipment failure; no refrigerant leak; no compressor or fan motor issues. Once filter replaced and coil thawed, equipment operated within all manufacturer specifications.
Customer Conversation
We discussed findings with customer:
Root cause: Dirty filter caused severe airflow restriction → reduced airflow across evaporator coil → coil temperature dropped below freezing → ice formation on coil → ice blocks remaining airflow → cooling capacity collapses
No equipment damage: The frozen coil scenario fortunately caught early — extended operation with frozen coil can cause compressor damage from liquid refrigerant return, evaporator coil damage from ice expansion, indoor flooding from ice melt overwhelming drain capacity
What we found vs. what we didn’t find:
– Found: severely dirty filter as root cause
– Did NOT find: refrigerant leak, compressor problem, evaporator coil damage, fan motor issue, or any other equipment failure
Preventive recommendations:
– Monthly filter checks during cooling season
– Filter replacement every 1–3 months depending on home conditions (pets, allergies, construction nearby)
– Consider 4″ media filter housing for less frequent filter changes if customer prefers (similar to Magna duct cleaning case study)
– Annual maintenance plan tune-ups catch filter neglect and other developing issues
Service and Final Cost
Work performed:
- On-site diagnostic with measurements
- Air filter replacement (new pleated 1″ filter)
- Verification of system operation across all parameters
- Customer education on filter maintenance
- Recommendation for filter replacement schedule
Final invoice:
– Diagnostic visit (applied toward repair): $99
– Filter replacement: $18 (parts cost; labor included in diagnostic)
– Total: $117
Customer’s gathering: Indoor temperature reached 76°F by 6:30 PM, guests arrived to comfortable home.
Maintenance plan enrollment offered: Customer enrolled — $189/year includes 2 tune-ups, waived diagnostic fees on emergency calls (would have waived $99 on this call), 10–15% repair discounts, filter replacement reminders.
What This Case Study Demonstrates
- Diagnostic process matters — symptoms appeared to indicate major AC failure (water leak, ice, cooling failure during heat wave) but root cause was simple: dirty filter
- Honest diagnosis — no equipment work performed because no equipment was failing; filter replacement and verification was the appropriate response
- What we DIDN’T do:
- Did not recharge refrigerant (charge was correct)
- Did not replace evaporator coil (no damage despite ice formation)
- Did not replace compressor (operating within specifications)
- Did not recommend equipment replacement (14-year-old equipment in good condition)
- Customer education — filter maintenance scheduling prevents recurrence
- Reasonable pricing for actual work — $117 total for diagnostic + filter, vs. potential alternative outcome of recommended major repairs costing thousands
- Maintenance plan value — would have included filter reminders that likely would have prevented this scenario entirely
Follow-Up
Maintenance plan tune-up scheduled for following spring before next cooling season. Filter reminder system enrolled customer for monthly check reminders via SMS.
One-year follow-up after maintenance plan enrollment:
– Three filter changes during year (per customer’s revised schedule)
– No further emergency calls
– AC continued operating reliably
– Customer specifically appreciated the honest diagnosis vs. expectations of major repair
Why This Case Study Matters
Many AC “emergency” calls have similar root causes that less scrupulous contractors might use to recommend equipment replacement or expensive repairs:
Common “emergency” patterns with non-equipment causes:
- Frozen evaporator coil from dirty filter — symptoms look like AC failure; cause is maintenance issue
- Frozen coil from blocked return air — furniture or rugs blocking returns produce similar symptoms
- Low cooling from cottonwood-loaded condenser coil — symptoms include reduced capacity; cleaning resolves
- AC short-cycling from oversized equipment — symptoms include comfort complaints; fundamental design issue, not failure
- Refrigerant pressures off from outdoor temperature extreme — symptoms can include reduced capacity at extreme temperatures; equipment operating normally
A diagnostic-first approach identifies which scenario applies, leading to appropriate response — filter change, coil cleaning, configuration adjustment, or actual repair if equipment failure is present.
Need Emergency AC Service?
If you have an AC issue in Magna, contact us or call (385) 250-0687. Diagnostic-first approach identifies actual problems rather than recommending unnecessary repairs.
- Phone: (385) 250-0687
- Address: 4454 Manhattan Ct, West Valley City, UT 84120