AC Replacement Case Study — 1980s Rambler, West Valley City

A West Valley City customer in a 1985 rambler on the west side called us in late June after their original-installation R-22 AC system failed during a heat wave. The compressor was drawing high amperage and the system was unable to maintain setpoint despite running constantly during 95°F+ afternoons. The system was 38 years old at the time of failure — well past typical service life for residential AC equipment — and the customer was ready to replace rather than continue investing in old R-22 equipment.

This case study documents the diagnostic process, equipment selection conversation, installation work, commissioning measurements, and rebate filing on a project that’s typical of West Valley City AC replacements when older systems reach end of service life.

Customer Situation

• Home: 1985-built rambler, approximately 1,650 sq ft single-story, west side of West Valley City
• Existing equipment: Original 1985 R-22 split-system AC, 3 ton outdoor condenser, matching evaporator coil; existing 1985 atmospheric-vent gas furnace (still operational, not being replaced)
• Symptom: AC running constantly during summer heat without maintaining 76°F setpoint; high electric bills; compressor making unusual noises
• Customer priorities: Reliable cooling, reasonable cost, willingness to consider efficiency improvements with payback period under 10 years

Diagnostic Visit

Date: Late June, mid-afternoon

Measurements documented:
– Outdoor temperature: 94°F
– Indoor temperature: 79°F (setpoint 76°F)
– Suction pressure: 78 psi (R-22, target 70–75 psi at these conditions)
– Discharge pressure: 295 psi (high — target 250–275 psi)
– Superheat: 22°F (high — target 8–12°F suggesting low charge)
– Compressor amp draw: 17.2 amps (nameplate 14.5 amps — drawing 19% over nameplate)
– Temperature differential across coil: 12°F (target 18–22°F)
– Capacitor: testing within tolerance

Findings:

The system was undercharged due to a slow refrigerant leak that had developed over years of operation. Combined with the compressor drawing over nameplate amperage and the system age, the equipment was at end of service life. We discussed options with the customer:

1. Refrigerant recharge — $400–$600 with leak repair attempt, but R-22 at $200/lb made this expensive, and the underlying compressor issues meant the system would likely fail completely within 1–2 seasons
2. Complete AC replacement — $5,500–$10,500 depending on equipment tier, addressing both refrigerant and compressor issues with current equipment

The customer chose replacement.

Manual J Load Calculation

On-site load calculation performed:

• Conditioned area: 1,650 sq ft
• Insulation: R-19 walls, R-30 attic (original 1985 construction, not upgraded)
• Windows: Original aluminum double-pane, 195 sq ft total glazing
• Orientation: Long axis east-west, primary glazing east and west exposures
• Infiltration: Average for vintage (3.5 ACH50 estimated)
• Salt Lake design conditions: 96°F outdoor / 75°F indoor cooling

Manual J result: 2.5 tons cooling load (30,000 BTU/h)

The existing 3-ton unit was 20% oversized for the actual load — common finding on installations from this era when contractors sized by rule of thumb rather than actual load calculation. Right-sized replacement equipment would be 2.5 tons, not 3 tons.

Equipment Selection

We discussed three equipment tiers with the customer:

Option 1: Single-stage 14.3 SEER2 (Goodman GLXS3BA3010) — $6,200 installed
– Standard residential efficiency
– Single-stage operation
– 10-year parts warranty
– Minimal qualifying for federal 25C credit

Option 2: Two-stage 16 SEER2 (Trane XR16) — $8,400 installed
– Better dehumidification through extended low-stage operation
– Quieter operation than single-stage
– 10-year parts warranty
– Federal 25C tax credit $600
– Rocky Mountain Power Wattsmart rebate ~$150

Option 3: Variable-speed 18 SEER2 (Trane XV20i) — $12,800 installed
– Best efficiency and comfort
– Communication system with matched furnace
– Best dehumidification
– 12-year parts, lifetime compressor warranty
– Federal 25C tax credit $600
– Rocky Mountain Power Wattsmart rebate ~$200

The customer selected Option 2 (Trane XR16 two-stage). The price difference vs. Option 1 was justified by efficiency improvement, dehumidification, and Federal 25C credit. The Option 3 premium wasn’t justified for the customer’s situation — their existing 1985 furnace doesn’t have a matched variable-speed blower, limiting the benefit of the highest-tier equipment.

Installation Day

Crew: Travis Hollings (lead installer), Cole Bennett (assistant)

Duration: 1 day, 7:30 AM to 4:00 PM

Scope of work:

1. R-22 refrigerant recovery from existing system per EPA regulations — recovered 6.2 lbs R-22 in DOT-approved recovery cylinder
2. Old equipment removal — outdoor condenser, evaporator coil from above existing furnace, original copper line set
3. New copper line set installation — 3/8″ liquid, 7/8″ suction sized for the new equipment per manufacturer specifications
4. New evaporator coil installation in supply plenum above existing furnace
5. New outdoor condenser placement on existing concrete pad (verified pad condition adequate)
6. Nitrogen purge during brazing — all joints purged with nitrogen at 5 PSI flow during brazing to prevent oxide formation inside copper
7. System evacuation — vacuum to 425 microns held for 30 minutes (passed at 425 microns rise to 480 microns, well within acceptable range)
8. R-410A charge — 9 lbs 4 oz per manufacturer specification for line set length
9. Electrical connections — disconnect verified, contactor wiring updated to new equipment
10. Condensate drainage — existing drain line verified, condensate pump tested (still operational, no replacement needed)
11. Smart thermostat upgrade — customer had purchased a Nest 3rd generation; we installed and configured for two-stage AC operation

Commissioning Measurements

After installation and 20 minutes of run-time stabilization:

• Outdoor temperature: 91°F
• Indoor temperature: 75°F (setpoint 74°F)
• Suction pressure: 132 psi (R-410A, target 130–140 psi at these conditions) ✓
• Discharge pressure: 365 psi (target 340–380 psi) ✓
• Subcool: 11°F (target 8–12°F) ✓
• Compressor amp draw: stage 1: 6.8 amps; stage 2: 11.2 amps (nameplate 12 amps) ✓
• Temperature differential across coil: 20°F ✓
• Static pressure: 0.42″ wc total (within manufacturer specification of <0.5″ wc)
• Refrigerant charge confirmed correct by subcool method

Verification: System operating within manufacturer specifications across all measured parameters. Two-stage operation confirmed — low stage activates first on thermostat call, high stage engages if low stage can’t satisfy within 20 minutes.

Final Cost and Rebate Filing

Customer’s out-of-pocket cost:
– Equipment and installation: $8,400
– Less $50 maintenance plan discount (customer enrolled at completion): -$50
– Net invoice: $8,350

Rebates filed on customer’s behalf:
– Federal 25C tax credit: $600 (customer claims on 2024 taxes)
– Rocky Mountain Power Wattsmart rebate: $150 (filed at completion, mailed to customer in 4 weeks)

Effective net cost after incentives: $7,600

Customer Outcome

Six-month follow-up (December same year, after summer use):

• AC maintained 74°F setpoint reliably throughout summer with sub-10 minute recovery from heat-of-day stretches
• Electric bills July-September averaged 22% lower than prior year (controlling for weather differences)
• Indoor humidity averaged 51% during cooling season vs. 58% with prior equipment
• Customer specifically appreciated quieter operation of two-stage equipment
• Smart thermostat learned daily patterns and reduced unnecessary cooling during away periods

Annual maintenance plan visit scheduled for spring before next cooling season.

What This Case Study Demonstrates

• Manual J load calculation matters — the old 3-ton unit was 20% oversized; replacement at proper 2.5 ton produces better dehumidification and lower run-time energy use
• Right equipment tier for the situation — Option 2 (two-stage) provided meaningful benefits over Option 1 with reasonable payback; Option 3 (variable-speed) would not have delivered proportional benefit given the existing single-stage furnace
• Documented commissioning — measurements verified equipment performance vs. manufacturer specifications, providing a baseline for future service comparisons
• Honest R-22 vs. replacement economics — repeated R-22 recharges on aging equipment with multiple developing issues would have cost more long-term than current refrigerant replacement
• Rebate filing matters — $750 in rebates and credits reduced net customer cost by 9%, more than the difference between equipment tiers
• Realistic expectations — 22% energy savings is significant but not the 50%+ claims that some marketing makes; honest projections build customer trust

Considering a Similar Project?

If you have an older AC system in West Valley City approaching end of service life, contact us or call (385) 250-0687 to schedule an in-home estimate. We’ll perform Manual J load calculation, discuss equipment options across price tiers, model applicable rebates and tax credits, and provide a written quote with the same level of detail documented in this case study.

• Phone: (385) 250-0687
• Address: 4454 Manhattan Ct, West Valley City, UT 84120

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