Background: Vehicle is 92 Civic with R-12 AC system. Compressor was replaced 2 years ago due to leak diagnosed there by AC technician (not sure if that was actually the problem). All but about 100g of refrigerant eventually leaked out again from the evaporator core, which I've now replaced (including thermal expansion valve). I evacuated the system with a vacuum pump, added 2oz of oil and refilled with about 620g of refrigerant (spec is 600-650g).
The system is working now, but has mediocre performance that's highly RPM-dependent. Over 2000 RPMs or so, the low pressure side drops below 40 psi and gets very cold. At lower RPMs, especially at idle, it stays above 55 psi and provides very little cooling.
I have some possible theories about what could be wrong, but I'm not sure how to diagnose which it might be:
- Contamination (air/moisture) in the system, perhaps from insufficient evacuation or air in manifold/hoses not fully expelled.
- Thermal expansion valve improperly installed. When I installed it I wasn't aware of how it was supposed to be positioned and clamped, so I just did my best to replicate the positioning of the old one and fastened it with the insulating tape (but no clamp).
- Bad seals in the compressor, maybe insufficient oil now or damage from loss of oil (lots seems to have been lost at the leak).
- Insufficient or over charge. I doubt this is the problem because I weighed the refrigerant while adding it, but I lost some at high side valve due to poorly fitted depressor in the manifold hose adapter, and condensation might have also messed up weights.
Can I rule out any of these right away? Or are there other possibilities I'm missing? What can I do to best narrow down the problem?
Some additional data:
Measuring now on a cooler day with 75°F ambient temperature rather than 90+°F, the low pressure side reaches 40 psi, but the compressor/condenser-fan stay on rather than cycling on/off. Reducing the fan speed from high to low makes the pressure drop to 34 psi. I think this strongly suggests insufficient insulation and/or poor heat transfer at the TXV bulb - it looks like increased air flow is warming the bulb and opening the valve.