A/C Compressor will not engage unless jumped at the relay

[heuster]

System just stopped blowing cold one day while sitting in the driveway.

All brand new components:
Compressor
TXV front
Dryer/manifold hose
Condenser
Freshly filled system with plenty of refrigerant

Here is what I've tested:
High side pressure switch - has continuity
Low side pressure switch - has continuity
Low side pressure switch - jumped compressor does not turn on
AC Relay - jumped 30 to 87 and the clutch engages and if the car is running AC blows cold
AC Relay - bought a new one, AC won't work
Tried to test power from the AC button inside on the dash with a test light but I couldn't really get a clear reading on it. Light on the dash does light up, is not blinking, but doesn't turn on the compressor when pressed.
All 3 AC related fuses are good. I pulled them all and tested continuity on each one. All good.

My gut says that the evap temperature sensor decided to die so it won't allow the AC to engage because it's stuck open?

QUESTION: If this is the issue, how do I test this? Does anyone have any pictures of where this sensor plugs in at so I could jumper it and test to see if that allows me to control the AC from the dash? My luck is terrible with cars. I have an evap leaking on my 01 so dash has to come out. I'm trying to avoid doing 2 dash removals. No thanks.

Any help would be greatly appreciated!

Oh and I also tested the AC related diode on the same fuse block as the AC relay. It's a one way diode that I've seen YT vids about it causing intermittent AC issues. Tests good...I get about 77 Ohms and then when I flip the fuse/diode I get 0 Ohms...as expected.

 

[SafariGoneWrong]

I like your approach and methodology. I'd be going for the evap temp sensor also. Mine is an '06 XLT; nevertheless, thought I'd attach what the shop manual says for mine. Glovebox removal...

 

[heuster]

I like your approach and methodology. I'd be going for the evap temp sensor also. Mine is an '06 XLT; nevertheless, thought I'd attach what the shop manual says for mine. Glovebox removal...

Thx man, I'll check this out!!

 

[Hamfisted]

Here's the voltage and resistance number chart if you want to test it with a multimeter before removing and replacing it.

Ford Evap Temperature Sensor Test Chart


Evap Temp Sensor Replacement









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[heuster]

Thanks, super helpful. Do you know which wires to test for resistance? It's a 3 wire plug but I'm not sure which ones should show resistance. Do I just start probing them all and if I get no resistance on any of the combinations the sensor is bad? Trying to remove as much of the guesswork on this as I can.

 

[SafariGoneWrong]

I found these evap sensor pinpoint tests for the '06. I'll keep looking some more. Of course, there may be more going on than the evap temp sensor.

 

[SafariGoneWrong]

Continuation of the previous.

 

[heuster]

Thanks!

 

[Dustin Gebhardt]

The circuit for the AC clutch engagement is pretty straightforward and linear. Switch A leads to switch B, etc. You’ve already tested a bunch of the items but I’m unclear if you found one that has power coming in but not coming out?

I replaced my dieing evap temp sensor on my ‘07. I started jumping it with a small resistor, thinking that I had to pull apart the dash to get to it. Eventually I decided to attempt the removal with just the glove box out and wouldn’t you know it, it came right out. The new one went right in. Easy peasy. I had discovered that the sensor was reading abnormally low, causing the system to kick off prematurely I backprobed with my multimeter and found that it was the cause of my failure to engage the AC clutch.

 

[heuster]

Did you test with the multimeter when it was plugged in? I tried testing it over the weekend while it was dipped in a bowl of ice and didn't get the readings that check out on the chart. I'm not sure I'm testing correctly - I had the meter on the two outside pins for around 5ohms and the inside and one outside pin were at 15 ohms.

I'm not sure where to test for power coming out? Do you mean out of the AC Relay?

 

[heuster]

The circuit for the AC clutch engagement is pretty straightforward and linear. Switch A leads to switch B, etc. You’ve already tested a bunch of the items but I’m unclear if you found one that has power coming in but not coming out?

I replaced my dieing evap temp sensor on my ‘07. I started jumping it with a small resistor, thinking that I had to pull apart the dash to get to it. Eventually I decided to attempt the removal with just the glove box out and wouldn’t you know it, it came right out. The new one went right in. Easy peasy. I had discovered that the sensor was reading abnormally low, causing the system to kick off prematurely I backprobed with my multimeter and found that it was the cause of my failure to engage the AC clutch.

Any chance you to how to test the sensor? I've gone through these sheets 100 times and just can't come up with an answer that tells me where my problem is. Did I test it right? cause I'm lacking in my sensor testing skills...

 

[Dustin Gebhardt]

For the evap temperature sensor, it’s a simple resistor that changes value with temperature. IIRC, a simple paper clip jumper will cause the sensor to read “warm” and cause the circuit to engage.

I think I clipped my multimeter to the sensor and placed it in my freezer. This gave me a rough range for resistance and I was able to buy a small 1/8 Watt resistor of a suitable value to trick the system into running until I fixed the sensor. It’s a fairly cheap sensor if you wanted to load up the parts cannon and just replace it.

 

[heuster]

Update on this:
I bought OBDLink EX and installed FORScan. Ran the key off self-test and everything checks out. Compressor clutch pulls back and everything which means the PCM is doing it's job and so is the relay. I monitored some PIDs that Makoluko from YT said to monitor...not sure what it's telling me is wrong, but I can't find it.
ACCLT_ALW = YES
ACCS = OFF
ACP = OPEN (OK)
WAC_F = No Fault (Wide Open Throttle A/C Cut-off fault)

If I read this right, ACCS should be ON. It's as if the system thinks that there is no pressure in the system, when there is. It's full. I removed the pigtail on the low pressure switch and jumpered it. Clutch didn't engage when jumpered. WHAT.
EVAP thermostat has been replaced
Should WAC_F read a diff value? Could it think that the pedal is all the way to the floor? Is there something wrong with the PCM?

HELP

 

[Hamfisted]

Is the AC Compressor switch ON on the AC head unit ? 'Cause it thinks it's OFF.
That will not turn your compressor on. So it could be just a bad head unit.
Is the little green LED lit up on the push button switch ?

 

[heuster]

Is the AC Compressor switch ON on the AC head unit ? 'Cause it thinks it's OFF.
That will not turn your compressor on. So it could be just a bad head unit.
Is the little green LED lit up on the push button switch ?

Yes, the amber light on the AC control is on along with one other light with related controls. I can push the A/C button and turn the light on and off.

 

[Hamfisted]

Ok. You should see the ACCS going from OFF to ON when you turn it on. Do you see any response ?

 

[heuster]

Ok. You should see the ACCS going from OFF to ON when you turn it on. Do you see any response ?

Nothing. The ACCS PID does not ever change.

Not to complicate the troubleshooting effort, but I've started to have random issues with the rear gate and steps opening. Sometimes when you open the door they just won't respond. Shut off the key, and turn it on again and they are fine. Related? I already did the patch job on the wire loom in the passenger door floor sill. I have stopped getting the "door sensor" message since I did the wire loom fix.

 

[Hamfisted]

Just confirm what year and model Expy you're working on. 'Cause you posted in the Gen2 Expedition section.
But I'd try a different head unit.








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[heuster]

Just confirm what year and model Expy you're working on. 'Cause you posted in the Gen2 Expedition section.
But I'd try a different head unit.

Gen1 HVAC Head Unit on eBay








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2005 Lincoln Navigator 2WD

 

[heuster]

Just confirm what year and model Expy you're working on. 'Cause you posted in the Gen2 Expedition section.
But I'd try a different head unit.








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Is there a way to confirm that the button is the source of the problem? All the lights work on the climate head unit. While the AC was running, it just turned off and stopped working. Just want to try and be sure before I spend $130 on parts.