The A/C won't blow cold air and sure enough, the expansion valve looks frosty. Your gauges confirm your suspicion that there’s probably a restriction: the low-side pressure is very low and the high-side pressure is higher than it should be.

Maybe the valve is stuck in the closed position, the filter screen is clogged (block type expansion valves do not have filter screens), moisture in the system has frozen at the expansion valve orifice, or the sensing bulb is not operating. Regardless, you need to find the cause and fix the problem. Here’s where to start:

1. Warm the diaphragm and valve body in your hand or with a heat gun (careful!). Activate the system and watch to see if the low pressure gauge rises.

2. Next, spray a little nitrogen or any substance below 32 F on the capillary coil (bulb) or valve diaphragm. The low-side gauge needle should drop and read at a lower (suction) pressure. This indicates the valve was partway open and that your actions have closed it. Repeat the test, but first warm the valve diaphragm or capillary with your hand. If the low-side gauge drops again, the valve is not stuck.

3. Clean the surfaces of the evaporator outlet and the capillary coil or bulb. Make sure the coil or bulb is securely clamped to the evaporator outlet tube and the insulation is in place. Next proceed with recovering refrigerant from the system.

Making the Repair

If the expansion valve has a screen (again, block-type valves do not), recover all refrigerant from the system and disconnect the inlet hose fitting from the expansion valve. Remove, clean and replace the screen, then reconnect the hose. Any sign of contamination will require flushing the system. 

Next, replace the receiver-drier, evacuate and recharge the system with refrigerant, and check the A/C operation and performance.

If the expansion valve tests did not cause the low pressure gauge needle to rise and drop, and if the other procedures described did not correct the problem, the expansion valve is defective. Recover the refrigerant from the system again and replace the expansion valve and receiver-drier (talk to your Red Dot distributor about sourcing the part you need). Evacuate and recharge the system with refrigerant and check A/C operation and performance. Let the cold air blow!

Maintenance