Alright, so I posted up a while back that I was having AC issues. It ended up working again, then after about a week I started getting Intermittent compressor clutch engagement while either of the A/C options are selected on the dash, and now it seems to work less and less frequently. Sometimes, I can even switch from vent air to ac back and forth and it will start running and produce nice cold air.

I can't seem to figure out why in the world the compressor will run SOMETIMES with the AC selected. I can't link it to any other conditions (hot engine, cold start, etc), it appears to be completely random.

Also, the truck has recently developed an intermittent hesitation at low rpms. Sometimes I pull away from a stop and all is well, other times I pull away and it shudders slightly, or the rpms will vary while pedal position is constant. It's very odd. It hasn't stalled yet, but there have been moments where it's been close. At cruise, it appears to be fine. Pulled the codes and got the following (P0135 "Oxygen Sensor Heater Bank 1 Sensor 1", P0132 "Oxygen Sensor Heater Bank 1 Sensor 1 Shorted To Voltage")

These issues seem to be connected. I thought maybe a vacuum leak was the answer, but didn't find anything in the engine bay or under the truck (sprayed vacuum lines with starting fluid while listening to the idle). I'm sure there are vacuum components in the dash that operate things since I can hear them when you turn on the AC, so maybe there's a vacuum leak in the dash?

Also, I'm thinking it might just be the PCM going bad...I honestly don't know though.

I cleaned the PCM grounds and made a nice new connection to the valve cover bolt for the ground on the passenger side just to be safe. Doesn't seem to matter. In fact, after I had the battery ground off for a while fiddling with all of it, when I restarted the truck, it almost wouldn't start. Eventually it did with a little throttle, but kept wanting to die. After a trip around the block it seems to be back to normal.

Thoughts?

 

How are a/c pressures? Does it work good when it works? Might just be a bad connection somewhere..... be it one of the connectors, or a ground, or even the switch in the dash.

 

Works great when it works. The difference is just whether or not the compressor will kick on at all. Sometimes, I'll be driving along with it keeping me nice and chilly...then slowly realize I'm getting moist because it's not longer running and drying the air, then it starts blowing hot. It will just stop.

Also, with the Trouble codes, what's the likelihood that the PCM isn't at fault and it's literally just an issue with the O2 sensor itself?

 

The O2 codes generally indicate a bad sensor.... if they are original, wouldn't hurt to replace them. (NTK or Denso please. Skip the bosch.)

Probably going to need to check voltages on the a/c system when it decides to stop working.

What year is your truck?

 

Alright, thanks. The truck has burnt a decent bit of oil for a long time (bad plenum for years until recent fix) so I'm not surprised the O2's are having issues. I'll get the O2's on order. They aren't that expensive anyway.

Yeah. I'll work my way back from the compressor in a couple days.

2001 1500 5.9 gas.

Any reason to replace the downstream O2 sensor since it doesn't actually provide input to the A/F ratio (as far as I know)? Funds are a bit tight at the moment.

 

Do what is within budget. If the PCM isn't whining about the rear O2 sensor, don't worry about it.

01 has two separate circuits that control the compressor. One circuit goes thru high/low pressure switches, and is monitored by PCM. Second is the relay, which is PCM controlled. (that actually provides power to the compressor.) Might be as simple as a failing relay.

 

Ended up just ordering both(ntk). If the back goes bad I don't want to pay the extra shipping to order it later.

Switched the relays around and it still didn't work. Fuse is also good. Didn't have voltmeter so have tested anything else yet.

 

Gonna need one.

Check the ground for the compressor.

 

I've got one, I was saying I didn't have it with me earlier. Haha!

 

Yeah, it works a lot better when you have it in hand.