Automotive Air Conditioning Information Forum

I have a 1998 k1500 that I replaced the compressor on recently. I also replaced the condenser, evaporator core, heater core and all the hoses. Basically, everything is brand new. I drew a vacuum and it held. I started changing the system, but could only get it to take one can of Freon. That was late yesterday. This morning, I tried again and was able to get it to take more Freon. The compressor was cycling on and off quickly. It was on for about 3 seconds and off for about 3 seconds. At the end of the second can of Freon, it came on and stayed on. When the compressor is on, the low side is about 40 psi and the high side is close to 200. When it’s off, the low side is 80 psi and the high side is 100. The odd thing is it’s not blowing cold air. Any thoughts? I have about 25 ounces in the system, and the capacity is 32 ounces.

Hopefully you vacuumed for at least an hour. Did you dump out the shipping oil and refill with the correct amount of oil, hopefully.

In any event you are still undercharged and you will not get cooling until you install the full amount of refrigerant

Also when you give us pressures please set to max cool and max fan. Recirc set, doors open, rpm at 1800.

A couple additional questions come to mind: Did you replace the Orifice Tube, or clean the original one? (It's in the evaporator.) Did you re-install it in the right direction?

The correct OT should be black where the screen is, white where the brass tube is (indicating a .072" orifice), and have a single o-ring.

JohnHere wrote: ↑Thu May 30, 2024 12:24 pm A couple additional questions come to mind: Did you replace the Orifice Tube, or clean the original one? (It's in the evaporator.) Did you re-install it in the right direction?

The correct OT should be black where the screen is, white where the brass tube is (indicating a .072" orifice), and have a single o-ring.

On those trucks it is actually very easy to get the lines swapped at the condenser, resulting in no cooling. Although that usually results in extremely high pressure on the high side and lower than normal pressure on the low side. I have actually worked on a few of these trucks that someone had backwards.

While the 0.072" is correct per the book and some would claim it is wrong, I stopped using the white orifice over 15 years ago on GM R134a systems. I run the Cadillac yellow 0.062" unit in those trucks as it noticeably improves cooling, especially in stop and go DFW traffic where ambients frequently hit a 120+F over the pavement. I have put 150K miles on my personal using one with no issues, only improved cooling performance. When the low side will not drop below 50-60 psi with everything working correctly, R134a suffers drastically in cooling performance.

A new condenser comes with a new OT in condenser outlet- make sure you don"t also have one in-line in front of Evap.

Always good to see you, GM