Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1984SUBURBAN C2500, 6.2 J, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)HEATING, VENTILATION & A/C (HVAC)GENERAL SERVICINGA/C SYSTEM GENERAL SERVICINGA/C SYSTEM DIAGNOSIS WITH GAUGES
1984 GMC Suburban C2500, 6.2 J, 400/M40
A/C System Diagnosis With Gauges
1984 GMC Suburban C2500, 6.2 J, 400/M40SECTION A/C System Diagnosis With Gauges
DIAGNOSIS WITH GAUGES - SYSTEMS WITH INSUFFICIENT OR NO COOLING
| LOW SIDEGAUGE | HIGH SIDE GAUGE | OTHER SYMPTOMS (1) | DIAGNOSIS | ||
|---|---|---|---|---|---|
| Normal | Normal | No or few bubbles in sight glass. High side gauge may go high. Low side gauge does not fluctuate with compressor on/off cycle. Cools okay in morning but not during hot part of day. | Some Air and Moisture in System | ||
| Normal | Normal | Tiny bubbles in sight glass. Discharge air warm when low side gauge drops into vacuum. | Excessive Moisture in System | ||
| Normal | Normal | Thermostatic switch system only-compressor cycles off and on too rapidly. | Defective Thermo- static Switch | ||
| Low | Low | Bubbles in sight glass. Outlet air slightly cool. | Low R-12 Charge | ||
| Low | Low | Sight glass clear or oil- streaked. Outlet air very warm. | Excessively Low R-12 Charge | ||
| Low | Low | Outlet air slightly cool. Sweating or frost at expansion valve. | Expansion Valve Stuck Closed. Screen Plugged or Sensing Bulb Malfunction | ||
| Low | Low | Outlet air slightly cool. High side line cool to touch. Sweating or frost on high side. | Restriction on High Side. | ||
| Low | High | Evaporator outlet pipe cold. Low side goes into vacuum when blower is disconnected. | STV Stuck Open | ||
| High | Low | Evaporator outlet pipe warm. Outlet air warm. | STV Stuck Open | ||
| High | Low | Noise from compressor | Compressor Malfunction | ||
| High | High | Outlet air warm. Liquid line very hot. Bubbles in sight glass. | Condenser Malfunction or R-12 Overcharge | ||
| High | High | Outlet air slightly cool. Bubbles in sight glass. | Large Amount of Air and Moisture in System. | ||
| High | High | Outlet air warm. Evaporator outlet | Expansion Valve Stuck Open. | ||
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RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.