I did some forum searching and found a lot of talk about freon charge in the system, but I'm puzzled if that would be my case, so I started this thread.

This past weekend I dug in and replaced my blend door and heater core. My truck is a '99 F150 4x4 offroad, 4.6L V8. The blend door was broke, and I did the heater core while I was in there. I disconnected battery, drained coolant, pulled dash, replaced parts, replaced dash, flushed coolant system, reconnected battery, and tested system. The good news is the blend door works now and the connections to the heater core don't leak, all is good.

However, now the A/C won't work. When I put it on A/C, I hear the switch click to turn it on, the compressor spins for about 1-2 seconds, then the switch clicks again and shuts it off. Repeat 5-6 secs later. The clicking is near the floor on the passenger side. Web searching and a call to a few car buddies points to low or high charge in system, with one of the sensors kicking it back off when it starts to spin up. I don't have pressure gauges or experience in this, so I can't immediately test and will get help if I need to. But I'm inclined to think this is electrical since I didn't touch anything in the A/C loop (I think) and don't know how freon could be lost. A/C worked up to this point, blowing good and cold when the blend door happened to swing correctly to allow it. Fuses are all good, and it's obviously getting power b/c it's switching on and off. Could a switch/relay have blown when I reconnected to battery? I know the computer has to relearn all of it's driving settings . . . could it possibly play a part in switching it off?

One thread I found did talk about quirky actions with a low battery. I did have to jump it on the first restart, but it wasn't completely dead b/c it was running all of the other subsystems. I jumped it by the book, and it started fine after that. When I hooked up the charger later, it said 90% battery at 12.7V and only took a little while before it shut off at 100%.

Anyway, I'm just looking down the electrical path first since it was working fine, and I'm comfortable working with electrical stuff. If that turns out fruitless, I'll go over to my buddy's house who has the gauges to test the freon pressure.

 

A short-cycling compressor clutch means the refrigerant charge is too low.

Steve

 

Yeah its probably the low pressure switch located on the A/C canister type thing, once the refrigerant gets below a certain pressure/point the switch engages and is deisgned to prevent damage to the system.