Trouble with AC in excursion swap

kasey200

kasey200

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Sep 24, 2006
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i've done a lot of searching and haven't found anything about this.

My A/C compressor won't stay engaged while at an idle. It will engage for <1 second and then disengage and repeat that over and over. I had the system re-charged after the swap and it will blow ice cold when you're driving down the road, but if your in stop and go traffic on a hot day it will cook you out!! Does anybody know where i can start looking? I don't know much about A/C systems.

The high pressure and low pressure switches are from the ford 6.0l A/C system. The only dodge part is the pump. The guy that did the A/C re-charge for me said he thought I could bypass the low pressure switch but i'm not 100% sure what he's referring to.

Thanks in advance
 
When the clutch engages and disengages every second or so is usually a sign of low 134a. It could be the low pressure switch but I would start with the freon. check the pressure on it.

I guess there could be a problem with your tach sensor did you run your cam and crank sensor wires together? What are you using for your tach?
The pcm needs a tach signal to allow the ac to work.
 
04fummins said:
When the clutch engages and disengages every second or so is usually a sign of low 134a. It could be the low pressure switch but I would start with the freon. check the pressure on it.

I guess there could be a problem with your tach sensor did you run your cam and crank sensor wires together? What are you using for your tach?
The pcm needs a tach signal to allow the ac to work.
Click to expand...

I don't think it's low on 134a as it was just recharged.

Tach sensor maybe... I bought the tach sensor from ford cummins and it doesn't work very well. The tach bounces around all over the place. Yes the cam and crank sensors are ran together.
 
kasey200 said:
I don't think it's low on 134a as it was just recharged.

Tach sensor maybe... I bought the tach sensor from ford cummins and it doesn't work very well. The tach bounces around all over the place. Yes the cam and crank sensors are ran together.
Click to expand...

Try seperating the cam and crank wires run them in seperate loom until you have to tie them together at the sensor there might be some cross signals even though they are shielded (did you leave the shielding on both). I have also heard that the shielding might cause the problem but I would first seperate the two.

hope that helps.
 
I don't recall whether or not the sheilding is in tact. I will check it out and separate the two wires. It seems like there could be some sort of interference going on there however i never thought of that.
Thanks
 
The shielding will be a bare copper wire and a foil tape and both the + and - wires are then wrapped together with a plastic tape. I have not tried this yet on mine but I was told that if you don't seperate them (crank and cam wires) you could have issues like you are having.
 
I have a similar issue on my 06. I cant get the compressor to come on at all. I have wired the compressor to an upfitter switch for the time being so my ac works. Be interested in what you find out.
 
A/C Cycling Switch
The A/C cycling switch is mounted on a Schrader valve-type fitting on the side of the suction accumulator.


A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem.
This allows the suction pressure inside the suction accumulator to control the operation of the A/C cycling switch.
The electrical switch contacts open when the suction pressure drops, the contacts close when the suction pressure rises.
When the A/C cycling switch contacts close, the A/C request signal circuit is completed to the PCM.
When the A/C cycling switch contacts open, the A/C request signal circuit is interrupted and compressor operation stops.
The A/C cycling switch will control the A/C evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
This prevents icing of the A/C evaporator core and blockage of air flow.
It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.
A/C Pressure Cutoff Switch
The A/C pressure cutoff switch is used to interrupt the A/C compressor operation in the event of high system discharge pressures.


The A/C pressure cutoff switch is mounted on a Schrader valve-type fitting on the high pressure side of the A/C manifold and tube.
A valve depressor, located inside the threaded end of the A/C pressure cutoff switch, presses on the Schrader valve stem.
This allows the A/C pressure cutoff switch to monitor the compressor discharge pressure.
When the compressor discharge pressure rises, the switch contacts open and the A/C request signal circuit to the PCM is interrupted. When the pressure drops, the contacts close to complete the A/C request signal circuit to the PCM.
It is not necessary to discharge the refrigerant system to remove the A/C pressure cutoff switch.
Dual Function Pressure Switch
The dual function pressure switch (DFPS) is used to interrupt A/C compressor operation in the event of high system discharge pressures.


The dual function pressure switch is mounted on a Schrader valve-type fitting on the high pressure side of the compressor manifold and tube assembly.
A valve depressor, located inside the threaded end of the DFPS, presses on the Schrader valve stem.
This allows the DFPS to monitor the compressor discharge pressure.
The DFPS has 2 sets of electrical contacts. One set of contacts is normally closed and is used for A/C high-pressure cutoff.
When the A/C compressor discharge pressure rises, the switch contacts open, disengaging the A/C compressor. When the compressor discharge pressure drops, the switch contacts return to the CLOSED position and A/C compressor operation resumes.
The second set of electrical contacts in the DFPS is used for engine cooling fan control.
It is not necessary to recover the refrigerant to remove the DFPS.
 
thanks guys i don't have alot of time to work on this during the week but i'll let you know after the weekend!
 
You could bypass your low or high pressure switch, but why would you want to do that? Both are cheap(er) insurance.
 
Have you tried turning up the engine idle until the compressor cycles properly? Maybe the computer thinks the engine is below RPM to cycle.
 
You mentioned that your a/c worked while moving down the road and when your stopped it wont work, I would think your not getting enough air movement over the condenser. Check to see if your fan is working right.
 
Generally when an ac cycles on and off very quickly, it is due to low system pressure. Most low pressure cut out switches are set to around 10 psi. You say you just had the system charged, but that doesn't mean that there wasn't a leak and now you are low on freon. You can get a manifold gauge set for around 50 bucks from Harbor Freight, check the static pressure (when the vehicle is not running) and then start it up and watch the low pressure gauge. If you are sure the system is full of freon (should be evident from the static pressure check) then bypass the low pressure cutout switch and see what happens.
One more tip, a lot of times, the valves in the service ports are where the leak is. Check to make sure the service port caps are on tight because those are the seal for that spot. If the service ports have schrader valves, that's an easy fix.
 
crewgirl said:
Generally when an ac cycles on and off very quickly, it is due to low system pressure. Most low pressure cut out switches are set to around 10 psi. You say you just had the system charged, but that doesn't mean that there wasn't a leak and now you are low on freon. You can get a manifold gauge set for around 50 bucks from Harbor Freight, check the static pressure (when the vehicle is not running) and then start it up and watch the low pressure gauge. If you are sure the system is full of freon (should be evident from the static pressure check) then bypass the low pressure cutout switch and see what happens.
One more tip, a lot of times, the valves in the service ports are where the leak is. Check to make sure the service port caps are on tight because those are the seal for that spot. If the service ports have schrader valves, that's an easy fix.
Click to expand...

Thanks,
I have checked the systrm for leaks and put a gauge set on and they checked out good. Full charge. Also i've tried bypassing the low pressure switch with unsuccessful results. The input signal seems to be cycling. I think i have it narrowed down to an electrical issue. Possibly related to the tach signal.
I have a few things to try but i broke my collar bone a week ago so its almost impossible to turn a wrench right now.
Thanks again
 
Have you looked at a wiring diagram? Does the power go threw the switches then to the ECM that controls the relay that controls the cluch? I cant even get mine to come on. I can bypass the relay and it works. Looking at the pin out on my ECM it has two pins for the AC. One for presure and one for the cluch. I'm still trying figure out where it all comes into play. My tach is tied into the wire going to the cluster. So the ECM doesn't see the tach at all. :bang I hope you figure it out. Maybe it will help me.
 
Ruben774 said:
Have you looked at a wiring diagram? Does the power go threw the switches then to the ECM that controls the relay that controls the cluch? I cant even get mine to come on. I can bypass the relay and it works. Looking at the pin out on my ECM it has two pins for the AC. One for presure and one for the cluch. I'm still trying figure out where it all comes into play. My tach is tied into the wire going to the cluster. So the ECM doesn't see the tach at all. :bang I hope you figure it out. Maybe it will help me.
Click to expand...

i Had the diagrams when i did the wiring back in feb or so. I am told the PCM needs the tach input to know when the comp clutch can engage. that may be your problem? I will post when i get it figured out
 
Im just wandering if you can wire around the pcm and let the high and low switches control the compressor?
 
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