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Randall C
Randall C, ASE MasterTechnician
Category: Ford
Satisfied Customers: 12894
Experience:  35 years ASE Master Tech, Diagnostic , Electrical Specialist
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No power to the low pressure switch 05 expedition

Customer Question

No power to the low pressure switch 05 expedition
Submitted: 2 years ago.
Category: Ford
Expert:  Virtual Wrench replied 2 years ago.

Hi,

Is there power at the high pressure switch. Power comes from HP switch and to the low pressure switch. See diagram below

Click here

Let me know please

Customer: replied 2 years ago.
No power at high pressure switch
Expert:  Virtual Wrench replied 2 years ago.

be right back

Expert:  Virtual Wrench replied 2 years ago.

See if you have power coming from Pin #19 on the powertrain control module.

Customer: replied 2 years ago.
If it's the middle connector on the PCM pin 19, I have 12 votes
Customer: replied 2 years ago.
Facing te mounted PCM, what connector is it?
Expert:  Virtual Wrench replied 2 years ago.

Hi,

Does this have auto temp control or manual temp control?

Customer: replied 2 years ago.
Manual
Expert:  Virtual Wrench replied 2 years ago.

Thanks, ***** ***** see what i can find. Be back soon

Expert:  Virtual Wrench replied 2 years ago.

Here is what i can come up with. #19 is the tan/light green wire.

Click here

Customer: replied 2 years ago.
12 volts on pin 19. Continuity good from plug to switch but when connected no voltage at plug
Expert:  Virtual Wrench replied 2 years ago.

If you unplug the pressure switch is there power at the Tan/Lt Green pin?

Customer: replied 2 years ago.
No power at the plug! Went back and checked the PCM power again aNd it's 12 volts. Continuity good
Expert:  Virtual Wrench replied 2 years ago.

That wire goes straight from the PCM to the switch,,,,i'm stumped :-(

Customer: replied 2 years ago.
Exactly!
Expert:  Virtual Wrench replied 2 years ago.

I will see if anyone else has ever came across this before because it sure isnt making sense to me..good luck bud.

Customer: replied 2 years ago.
Thanks
Expert:  Randall C replied 2 years ago.

Hello, new expert here, The system is not setup with power from the PCM to the pressure switches persay, Hard to explain but the PCM is only reading pressure switch grounding, both switches, Power is not going to be present at either switch, It flows through small sensor on the HVAC case called the de icing sensor, so,, may I ask what is the problem at hand? why are you asking the question? what is not working and what all has been done? performed? thanks

Customer: replied 2 years ago.
No Ac
New compressor freon enough to trigger clutch.
Diode good and relay good left front.
By pass low switch,
nothing.
Expert:  Randall C replied 2 years ago.

remove the AC relay.any teminals have 12 volts

Expert:  Randall C replied 2 years ago.

did you bypass both high and low switches

Customer: replied 2 years ago.
both switches
Expert:  Randall C replied 2 years ago.

still need the volt test at relay

Customer: replied 2 years ago.
12 volts
Expert:  Randall C replied 2 years ago.

how many? 1?2?3? I am trying to gather as much informatiin as I can, Not being there.thanks

Customer: replied 2 years ago.
Next to the diode, I has 12 volts
Expert:  Randall C replied 2 years ago.

ok, you may be misunderstanding, Remove the AC relay , Turn key ON< probe the terminals the relay plugs into, How many terminals have power? is this what you did and only one does?Its the 5 prong relay

Customer: replied 2 years ago.
5 prong but 4 active plugs. 2 has 12 volts
Expert:  Randall C replied 2 years ago.

ok, good, now jump 30 and 87, I have diagram link included. Key ON, what does compressor do>? BTW: what are the freon pressure readings with engine off

Customer: replied 2 years ago.
Compressor activates
Customer: replied 2 years ago.
80 and about 70
Expert:  Randall C replied 2 years ago.

little low, is this with engine not running? if so. jump relay and get pressures up some maybe? 8 oz +/- you need to be around 100 both high low engine off. OR 45 low 200 high as an average only

Customer: replied 2 years ago.
Running at this point is 60 200
Expert:  Randall C replied 2 years ago.

ok, pretty close, like low side a bit lower but close., so,, the system does work, I assume you swapped relay? you have power to relay as needed, NO power goes the either switch, is does NOT work that way. so, need to locate the de icing sensor on front side of the HVAc case, unplug, turn key on, how many wires have 12 volts? see the link

Customer: replied 2 years ago.
None but rechecking.
Customer: replied 2 years ago.
1 has 12 v
Expert:  Randall C replied 2 years ago.

well, all I can say is... here is the diagram. "B" shown on the right is power to that sensor., That sensor controls a "GROUBD" to both switches. NOT 12 volts, The PCM reads a ground connection and controls the AC relay on the left side of the diagram, You seem to have everything so,, possibles are. icicng sensor is bad OR PCM is bad