Anyone had an issue with their AC cycling on and off at idle? I notice its worse the hotter it gets. When it does cycle, there's a distinctive "knock" sound coming from the passenger firewall area whenever the compressor cuts in an out. Compressor relay? Any ideas?

 

A/C will cycle on and off whenever the evaperator temperature rises to a certain point and drops to a certain point, respectively. This is normal. The knock sound you describe is probably not normal. Relays are rarely loud enough to hear when the vehicle is running. Either something is loose or the compressor is failing. Or, the knock sound you hear is the clutch engaging. Not sure if I can't actually hear the noise.

 

I'm having the same issue. Sounds like the relay is clicking. I'm thinking it's maybe the compressor clutch failing. I will troubleshoot tonight.

 

If i ever notice the compressor cycling on and off constantly it always ends up being that it needs refrigerant. Get a HVAC manifold gauge set and hook it up to your car. The pressures should be atmospheric pressure +- 10 degrees. If its not then you need to figure out were else the problem lies.

 

usually when they kick on and off they have to much refrigerent, have u messed with it lately or had it charged????

 

Turbodude06 hit it on the nail: Too much freon. When I hooked the gauges up, it was on the full/alert line. Removed some of the freon and now no more cycling. Todays ambient temparture was 95 degrees and no more cycling. The temp gauge in the center ac vent was 48 degrees. Problem solved for me.

To OP, you may have too much freon in your system. I would recommend you to get a gauge and check it out. Post back and let us know.

 

I also have an ac cycling issue. However, according to the pt chart, im low. Its very strange. If I run the suction at around 25psi, on a day like is was when i checked it of 85f, it was struggling but running. If I add freon to the correct psi for 85f ambient, suction around 40 psi, there is a nock on passenger side, near the front and ac kicks on, knock, off ect. I know the condensor fins are clear, all fans working properly and head was 225 which doesnt indicate a high charge. I have a feeling I have noncondensibles but this too give you a high, high side? I have some basic tools but not a vaccum pump to pull and dry system. Any other ideas? I have heard there is a swith that often fails on honda that acts this way too?

 

My ac okay. Dont follow temp/pressure chart. Start with a clean, dry vaccumed system and charge to about 25 psi suct. With a thermometer in a vent, ac on high, fresh air setting, continue to charge to around 35 suction and a vent discharge temp of around 52f. I charged on a 98f day and it now works great. It was cycling from high head as I overcharged it using the pt chart.

 

You should not guess when charging a system. You should charge the system by weight according to manufacturers specifications.