Strange A/C Issue - Cycling Compressor, any help?

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Karma Killer xx

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Hello to everyone at LVC. I have been lurking here for a few weeks. I finally purchased my '04 LS V6 less than a week ago and I'm in love. I got her from the dealership I work at- she was slated to go to the auction and I simply could not let that happen. I digress.

I've been trying to solve my A/C issue day by day.

The issue:
The compressor cycles way too often (especially since the compressor shouldn't really cycle much at all with this system). The compressor will come on for about 20 seconds then turn off for about 20 seconds (give or take a few seconds). When the compressor is running, the air through the vents feels cooled but not cold, about 70 degrees at idle and a few degrees cooler while driving on the interstate. Obviously the air from the vents should be much colder, but I figure the compressor running for only 20 seconds isn't allowing the air to get cold. This happens on both Auto and Manual adjustments.

What I've tried:
I work in a shop and have access to a Robinair A/C machine. I evacuated, vacuumed, and recharged the system to 28oz as recommended by Ford. Same issue, no change. I added a few ounces, one at a time to see if the system needed any additional "Suva", no change. While adding, the pressure of the high side (when the compressor was on) went from about 150 to over 200 as I added more R134a. No change (except I think I added more than she wanted because the air, while the compressor was running, wasn't blowing as cool as it was with 28oz) I then decided to evac, vacuum, and recharge to 24oz and slowly add Suva oz by oz until I reach 28oz. No change. The compressor still cycles often. I did an onboard diag via the interior A/C unit (DATC?) and received a 1265 - Cool Air Blend Door, which I've read on here and other places that it is not equipped on this vehicle. And SOMETIMES when I do the test I'll get a 2798, which is an issue with the DCCV. I say sometimes because I've done the self-diag about 15 times using both the stored and current options and have only received the 2798 twice. This may mean that my DCCV is hiccuping, but I highly doubt it is causing my current compressor cycling issue. Also, all of my vents seem to blow the same on and off "cooled" then "muggy" air. No heated air- and the heat does function very well when I've tried it.

My last though is that it might be a faulty Pressure Gauge. I tried unplugging it, and the compressor will not come on, and my fan speed increases significantly. I believe I can jump the connector using a 1.5v battery, but I haven't tried this and I'm not sure I want to.

If any more information is needed let me know. And thanks in advance for actually reading all that :D
 
The compressor will also cycle off if the evaporator temperature sensor reads too low. You may want to check that sensor.
 
Where is this sensor located? Would I be able to see it from the passenger side floor board? And do you know how I would test this sensor/can I just jump the plug that goes to it and see if the compressor stays running?
I surely can't imagine the evaporator getting too cold 20-30 seconds after I start the car/AC, but I suppose it could be a defective sensor?
 
Karma Killer xx said:
Where is this sensor located? Would I be able to see it from the passenger side floor board? And do you know how I would test this sensor/can I just jump the plug that goes to it and see if the compressor stays running?
I surely can't imagine the evaporator getting too cold 20-30 seconds after I start the car/AC, but I suppose it could be a defective sensor?
Click to expand...

The best way to test it is with a scan tool with live data readouts. See if the readings for evap temperature look sane. To get to the sensor, I think you have to tear much of the dash out. Jumpering it wouldn't work.
 
I have a couple scan tools at my disposal at work. I used a small Mac scan tool today to diag an issue I had this morning on my way to work. My car felt as if it was misfiring very badly after a hard brake, then it went into some type of limp mode where the throttle did not respond when depressed. After restarting a couple times everything was okay + a check engine light. Used the scan tool and found 3 codes. 2 related to the throttle actuator being stuck open, and stuck closed, and the third was stuck in idle. I imagine the electronic throttle body hiccuped causing the car to go to limp mode. I made it to work without any more issues, then I cleaned my throttle body thoroughly with intake cleaner and checked my connections. All seems well now. I was checking out the scan tool and didn't see anything for A/C monitoring, but there is a larger scan tool that may have that function. Would an A/C monitoring scan tool be plugged into the OBDII port to monitor the A/C? And would it be able to detect readings from my "refrigerant transducer"/pressure switch?

Thank you for your time Joegr
 
Yes, it can, from the OBDII port. I have AutoEnginuity, and as best I can recall, it reads these sensors and over 400 others.

I suspect that you'll find that your ETC problem is caused by one or more marginal coils, not a physical throttle problem. Your best bet is to replace all six coils and plugs. Note that coil problems are common. Also note that while rare, it is possible for coil problems to cause the PCM to turn the AC compressor off.
 
joegr said:
Yes, it can, from the OBDII port. I have AutoEnginuity, and as best I can recall, it reads these sensors and over 400 others.

I suspect that you'll find that your ETC problem is caused by one or more marginal coils, not a physical throttle problem. Your best bet is to replace all six coils and plugs. Note that coil problems are common. Also note that while rare, it is possible for coil problems to cause the PCM to turn the AC compressor off.
Click to expand...

Well Joegr, the A/C problem has been solved! I took your advice and hooked up a buddy's Solus scan tool and found that the evaporator temp sensor was reading 14 Degrees F. Once it hit 14 degrees the compressor turned off- then the temp slowly rose to 22 degrees and the compressor would kick back on- and the temp sensor would again drop to 14 degrees and the compressor would shut off. I sat there watching the live data for about 5 minutes to verify this was the issue. I located the evaporator temp sensor, unplugged it and started the car to run the A/C... VOILA! The compressor runs consistently and at about 2k RPM my registers are blowing 39 degree air. My question now is; What else does this evap temp sensor control? Does it effect the variable expansion valve or the variable scroll compressor (besides shutting it off when temps in the evap get too low)? I want to replace this sensor but am having some trouble locating it. MotorAllData doesn't seem to have a full part number for it. Also, any idea how to remove it from the evaporator case? I believe I should just be able to pull it out with some finagling, but I'm not sure what it even looks like inside the evap case and I'm worried about damaging something.

Back to the ETC issue: today my check engine light came on again while I was driving to work- luckily this time I didn't have to deal with the wonderful "limp mode". I read the codes when I got to work and found 2 codes, one was a 'misfire during startup (within first 1k revolutions), and the other was a "misfire in cylinder #1"... I have heard that the COP's are a common flaw with the LS. I'm surprised a misfire would cause a throttle issue- but then again, I'm surprised a lot. My first step is going to be pulling the plugs and seeing how they look. I have no maintenance records on the vehicle so I'd like to go through and do what I can afford, when I can afford it. I work in a shop and am mechanically inclined, so really I just need the parts. I know there's a pretty darn bad oil leak from the pan gasket and I'm reluctant to tackle this because I've read around that it's pretty extensive (about 4-5 hours of work, maybe more in my case).

Thank you for your wise words Joegr
 
coil and plug replacement is a pain on the v6, but leaving them in there will cause damage to your cats.

The evap temp sensor will have to be on the plenum inside the dash right after the evap core. You'll most likely have to remove the entire dash to get to it.
 
oddball said:
coil and plug replacement is a pain on the v6, but leaving them in there will cause damage to your cats.

The evap temp sensor will have to be on the plenum inside the dash right after the evap core. You'll most likely have to remove the entire dash to get to it.
Click to expand...

Getting to the sensor is easy. It right under the dash on the driver's side. The connector sticks out of the evap case. I can wiggle it, and I feel like if I pull/finagle it enough, it will come out. The A/C has been blowing nice and cold ever since I unplugged the sensor. But again, I'm not sure if this sensor tells the computer to do anything else except turn the compressor off if it's readings on the evap get too cold.

The plugs and coils will get done as soon as I can afford them. I'm looking at about $150 for 6 Visteon coils. I'd love to do Motorcraft, but I've heard a lot of good about Visteon, and they're about half the price if I buy the set. I've seen cheap sets going for about $60, but I'm very reluctant to try these.

MORAL OF THIS THREAD: If your A/C Compressor cycles on and off and your pressures are good- check your evaporator temperature sensor.
 
Just be careful that your evaporator core doesn't freeze over. That is entirely possible with this A/C system and can cause bigger problems.
 
TooManyToys said:
And what problems would that be? Just curious.
Click to expand...

The LS has no low pressure cut off switch. I don't know if having the low side go too low could damage the variable scroll compressor or not. If not, the main problem with having the evaporator freeze up is that the AC stops cooling until you turn it off and let it thaw out.
 
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