Hi,
Is it possible to disable the AC without damaging anything? Whether it be pulling the plug to the compressor or maybe a fuse? For some reason, I suspect it is running when I don't want it to. The hard pipes leading to the evaporator core are freezing and showing condensation on them like the AC is running but I don't have the controls on that setting. I believe it may be compromising my heat.

 

If you are on Defrost or Defrost-Heater, then the A/C compressor is going to run to dry out the air that is going on the windsheild. You can pull the plug to the compressor if you want to, it won't hurt anything, you just gotta plug it back in next Spring.

 

The A/C compressor won't run if the ambient temperature is too low.

 

Bill, are you sure that all systems have an ambient temp sensor that will cut out the compressor clutch current?
tom

 

Actually, I should rephrase that. There is a switch inside the evaporator core, attached to a line very near it or on another component so condensation doesn't freeze, expand and crack the core. That's even normal for summer usage. Something has to keep the core from freezing.

 

There are very few Fords of that vintage that actually have a temperature sensor in the evaporator core. Most simply have the low pressure cycling switch on the accumulator.

The 05 Escape has only the cycling switch.

 

Could the cycling switch possibly be stuck in the "on" mode? I have reason to believe that the AC is on in every position on the manual control selection switch. What leads me to think this is the hard pressure pipes are cold, sometimes with condensation on them. I also can't hear or feel any difference when I switch between the AC mode and the non-AC mode.

 

Well, if it makes any difference, I pulled the fuse that was labeled "AC clutch/AC relay. If the AC was on, that should have disabled it, correct?

 

The '09 Electrical Diagram shows a A/C Transducer. Both on a manual and auto climate systems show a evaporator discharge air temperature sensor.

Everything goes into logic and who knows what!

Although low side pressure or how low it is could be used to determine evaporator temperature, it wouldn't be very accurate or reliable.

 

That'll kill it for sure!

 

Although low side pressure or how low it is could be used to determine evaporator temperature, it wouldn't be very accurate or reliable.

The LPCO is used to monitor Low Pressure, and Cut Out power to the A/C clutch, very reliably. The boiling pressure of refrigerant is pretty well established, given there is room in the system to boil. R12 bp tracked pretty close to ambient temperature, such that the pressure at 32F was close to 32psi, FWIW. R134a is not so close.
So, if you did not want frost on your evaporator, AT ALL, you'd set the LPCO to cut power to the A/C clutch at 33psi. Viola. No pressure below 33 would be reached, so no frost. In theory. In practice I think the LPCO switches were set below that number so as to maximize cooling 'low temperature' with the heat of the air coming in melting any frost before it could build up. If you watch the low side line when the compressor first kicks in, if you have good refrigerant and a good compressor, the line will frost for a few seconds as the compressor sucks the pressure below the boiling point, and frost forms.
tom
p.s., the 1974 Pinto had an ambient temperature switch out in front of the radiator, near the hood latch to prevent A/C at lower temperatures. I have not seen any others...

 

Granted I haven't worked on anything "new" or an OEM R134A system. Like I stated the "09 has a evaporator air discharge sensor along with cabin temperature sensor(s) as well. It's used for something.

I removed a evaporator switch from a '78 Corvette, what a PITA with the capillary tube hose clamped to the low side of the evaporator covered with we called in the Navy, Monkey ****.

I read in a Porsche forum where some living in very warm areas have rigged a bypass on the clutch cycling switches to let the evaporator get as cold as possible but these are older Porsches.

If the LPCO is used at 32F, the static pressure of R134A is 27.7psi. Do you what's the OEM setting on the switch?

 

Systems that use TXV - thermal expansion vavles - generally have a pitot tube and bulb that is affixed to the evaporator core which regulates the valve feeding refrigerant into the evaporator. If it gets to freezing, the gas in the tube contracts, and somehow closes the TXV. Gets warm, expands, and opens the TXV. Keeps the evap very near 32F or whatever the temp specified.
I would suspect LPCO pressure cutout is pretty near 32F pressure, likely a bit below.
The cabin temp and discharge sensors in the 2009 are likely used in an automatic system that sets cabin temperature at a number, rather than the analog setting of manual systems. If the ECM or BCM gets into the picture, it may be monitoring discharge temp to 'know' it had better cut the A/C power as the evap is going to freeze up any second now... LPCO in that case would act as a protector. If you get the pressure too low, you are low on refrigerant, and will not be feeding the compressor refrigerant AND the ester/pag oil needed to keep the compressor lubed. The refrigerant carries the oil around the system, so if you have no refrigerant flow, you have no oil flow. The evap temp would be cold until there was no more refrigerant, but the key is the LPCO sensing pressure which the computer would not care about, but the compressor would.
tom

 

Both man/auto systems show the evaporator temperature sensor and a ambient temperature sensor in their circuit but the auto system has a in-vehicle temperature sensor also.

Every feeds into the HVAC Module on both systems.

 

The OP has a 05. The sensor was added in a later model year, but it does not apply this this particular conversation except as a sidebar.

Ford's cycling switches typically open around 20-25 psi descending and close around 40-45 psi ascending. You can work out the temps with an R134a PT chart.

If the problem was due to an electrical issue, yes. If it's due, for example, to a mechanically jammed clutch plate, then no.