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AC electrical issue

Tiny
PCDJ64
  • MEMBER
  • 2006 LINCOLN TOWN CAR
  • 4.6L
  • V8
  • RWD
  • AUTOMATIC
  • 367,000 MILES
System is full of R134, no leaks.
I press auto, AC and recirculate and the radiator fan and clutch do not come on, I get hot air.
I have temperature set to sixty and the outside temperature when I tried was seventy six.
if I unplug the high pressure switch the radiator fan turns on but not the AC clutch if I jump the relay for the AC clutch I get ice cold air.
I tried swapping relays and nothing changes, all of the fuses are good.
I did the self diagnostic test on the EATC and it passed with no codes.
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Monday, October 17th, 2016 AT 4:41 PM

7 Replies

Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Look for the low pressure switch. It us usually on the receiver drier. Disconnect the switch and with a small paper clip jump the two pins together on the connector. If the compressor comes on then the switch is bad. You can replace the switch without having to drain the AC system. Let us know how that test goes.
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Monday, October 17th, 2016 AT 4:45 PM
Tiny
PCDJ64
  • MEMBER
  • 127 POSTS
I forgot to mention, the first thing I tried was shorting the connector for the low pressure switch, it has three pins and the high has three pins, I tried all combinations with a paperclip on the low and nothing happened.
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Monday, October 17th, 2016 AT 4:51 PM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Forgot to add image. Four pin connector. Also if the switch is not on drier it will be on the low pressure hose. Pink with light blue stripe wire and other wire is violet.
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Monday, October 17th, 2016 AT 4:51 PM
Tiny
PCDJ64
  • MEMBER
  • 127 POSTS
I swapped out the low pressure switch, still the same result, no compressor or radiator fan. The fan is on when high pressure switch unplugged and cold air when relay removed and compressor fed power.
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Tuesday, October 18th, 2016 AT 7:09 AM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Check fuse 11 15 AMP in engine compartment and fuse 31 10 AMPS inside vehicle fuse box. If okay then you will need an advance scanner to look at data and see if the PCM is getting AC request from the climate head and to see if you can command the A/C clutch relay on and off with the scan tool. Once the PCM receives the AC request the the PCM grounds the relay so you could have an issue any where from the wiring to a faulty PCM. Also low refrigerant level will cause the PCM not to ground the relay. System needs to be evacuated to weigh the refrigerant so this can be something simple as a top off?
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Tuesday, October 18th, 2016 AT 9:39 AM
Tiny
PCDJ64
  • MEMBER
  • 127 POSTS
If refrigerant was low shorting the pins on the low pressure switch would activate the compressor.
Also, I do not think the air from the vents would be cold if it was low enough to stop the clutch from engaging.
I checked the fuses, they are all good, I tried swapping the diode, a friend of mine has a town car with working AC so I am not wasting money buying parts.
The PCM was replaced with one that was fully tested from another issue that the car had.
There is a ground diode I didn't touch because I am not sure it has anything to do with the AC.
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Tuesday, October 18th, 2016 AT 11:14 AM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
At this point you will need to take it in to a shop or try and get an advance scanner to look at the data I mentioned on last reply and to see if you can actually command the A/C clutch relay on.
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Tuesday, October 18th, 2016 AT 1:02 PM

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