How do you turn the ac compressor back on in a 94 eldorado once it is automatically turned off from low 134 a?

The A/C compressor in a 1994 Cadillac Eldorado (and most cars with automatic climate control) doesn't simply turn *off* because of low refrigerant. Low refrigerant triggers a safety switch, usually a pressure switch, that *prevents* the compressor from engaging to protect it from damage. Simply adding refrigerant won't automatically reactivate it.

Here's what you need to do:

1. Add Refrigerant (R-134a): You'll need a refrigerant charging kit with gauges. Do not simply add refrigerant without checking the system's pressure. Low pressure is a symptom, not the problem. There could be a leak.

2. Check System Pressure: Your refrigerant charging kit should have gauges to measure low-side and high-side pressure. These pressures need to be within the manufacturer's specifications (found in your owner's manual or a repair manual). Low pressure indicates a leak or insufficient refrigerant. High pressure could indicate a blockage. If pressures are off, you have a larger problem beyond just adding refrigerant.

3. Check the Pressure Switches: There are usually two pressure switches involved in the A/C system: a low-pressure switch and a high-pressure switch. If either is faulty, it could be preventing the compressor from engaging, even with sufficient refrigerant. These switches need to be tested or replaced if faulty. This often requires an automotive A/C professional.

4. Check the Clutch Relay and Compressor Clutch: The compressor clutch is electromagnetically engaged. If the clutch is not engaging, the relay supplying power to the clutch might be faulty. This requires testing the relay and potentially replacing it.

5. Check for Leaks: Before adding more refrigerant, you MUST find and repair any leaks in the system. Adding refrigerant to a leaky system is a waste of money and harmful to the environment. A leak detection dye or an electronic leak detector can help identify the source of the leak. Leaking systems often require professional repair.

In short: Simply adding refrigerant is likely not enough. You need to diagnose the *cause* of the low refrigerant (leak) and check the operation of the pressure switches, compressor clutch, and relay. Unless you have experience working on automotive A/C systems, it's highly recommended you take your Eldorado to a qualified mechanic specializing in automotive air conditioning. Attempting to fix it yourself without the proper tools and knowledge could lead to further damage or injury.