I have an 01 zr2 and I noticed the a.c. clutch engages for about 8 seconds then disengages but does this like every minute or so while driving. Very annoying power surge, and im sure its killing my mpg. Also the HVAC is stuck on face vents no matter where the **** is. I can year a hissing noise from behind the blend *** so is it just a vac leak? And quite often when I first start the truck the abs and parking brake warning lights come on and go off after driving for a while? Any help will be much appreciated.

 

The AC cluch cycling off and on like that probably means that the system is low on coolant. You'll want to get it serviced or recharged.

The HVAC is probably from a vacuum leak. If you hear hissing behind the controls it's probably a bad seal there. You can try replacing the seal, or maybe even the whole control unit if you can find a cheap used part.

ABS & park brake warning lights might be because of a bad hub, or maybe low brake fluid? I'm not sure on that one. You need to pull the DTC codes. If it turns on the warning light it should set a code in memory.

 

The AC cycling on and off is normal when you have your heater controls set to a defrost setting.

What El_Beautor said for the other 2 issues.

 

It is cycling the compressor with the heat/ a.c. turned completely off and or on any setting other than defrost. But like I said the mix kob does nothing due to the vac. leak.

 

If you're having problems with the HVAC controls, maybe you want to replace the controls first, and see if that solves your A/C compressor cycling before you go digging into the A/C system. It's possible you have a problem in the switch that is keeping the A/C on. The A/C compressor will cycle based on position, not temperature. It will always be triggered to cycle when it's in either defrost position, feet, or when A/C is selected.

What I said before about the A/C system cycling does stand though. When selected, if the A/C system has some, but low pressure, the compressor will turn on, but as it's pumping there isn't enough refridgerant to reach operating pressure so the compressor turns off. There can still be enough residual pressure to allow the system to start, but not to operate, so the compressor ends up cycling for only a second or two, then turning off, then trying again. Other symptoms will include your A/C not getting as cold as it used to, and maybe a musty smell when you try to use it. If you leave a leaky system, eventually it will lose all pressure, and your A/C compressor won't turn on at all.

Many parts stores carry A/C recharge kits that have a pressure gauge, so you can check your own, but if you have a system leak somewhere I'd recommend you go to a certified A/C technician who will be able to trace the leak and replace the necessary parts so you're not just constantly venting refridgerant into the atmosphere. They will use a UV dye to find any leaky seals. If you were in Calgary Alberta I could recommend a pair of fantastic A/C techs. I used to work with them and they are great, and will never over charge or recommend parts that you don't actually need.