AC Clutch Cycle and Pressure

I have a 1986 Bronco that I changed from v-belt to the 1994 style serpentine setup. In my experience, the old v-belt system that used an FS6 compressor never really cycled off unless the low-side pressure switch turned it off when something was wrong. The new system uses an FS10 copmpressor and has a place for a low- AND a high-side pressure cutoff switch.

I'm having a problem with the new system where after a while, the high-side pressure relief valve starts blowing out refrigerant and some of the UV PAG oil. So my question is this: is the newer system one that needs to cycle on and off like my '09 ranger does? Do I need to incorporate a high-side AC pressure cutoff switch into my wiring in order for the cycling to happen properly?

I am guessing you had the system open to swap in the FS10 compressor for the FS6 one?
How did you recharge the system and what was the gauge readings low / high sides?
How much larger is the 10 over the 6?

Got to ask why not change the pulley on the FS6 from V to serp?
Yes You would need to change the clutch but that is not hard and the system does not need to be open.
Dave ----

Heya, Fuzz!
I had the system open, but followed normal procedure in pulling a vacuum for 30 minutes, then leaving it to check for leaks (none found), then running it and adding until the pressures were around 45 and 200. I'm sure the pressure in the high side is much higher now that it is making the valve open. I have not checked it with my gauges yet. It's not a problem for me to open the AC, because I have access to an evacuation system, and I can recharge at home.

The 10 is not larger than the 6. It's just a newer design. If anything, I would say the diameter of it is smaller.

I had to switch because I was fixing 2 problems:
1. the brackets that held all the v-belt stuff were starting to fatigue. I had already welded them back together once and they were starting to crack again. (these brackets were run for all 600,000 miles of this vehicle's life).
2. Even before the metal fatigue, the belts were always squealing and out of alignment.

So I ended up just taking the whole front off the engine of a 1994 and using all the new accessories and updated designs. This also worked well with my saginaw compressor.

Also, the FS6 is a regular mount and the fS10 is transverse mount, so it def wouldn't swap over.

When I get home I can pull the mitchel drawing, but my 1995 Ranger has the FS10 setup with both switches.

The high side switch does the main regulation.... the low side is just to keep it from running with a low charge. They're wired in series as part of the clutch circuit.

Thanks, Ratman. I know how the wiring needs to be, but I was mainly wondering if the high side is necessary to cycle on and off. Because I don't have it currently.

Your post seems to indicate that the high side is necessary.

From my experience, yes.

I added the pressure switch and wiring and it all seems to be working right. Thanks again!

Larry - Can you post a pic of the high-side switch?  I have an FS10 system from a 1990 F250 in Big Blue and it doesn't appear to have that switch in it.  Or maybe I'm missing it?

Gary, here is the one on Darth, it is in the hose manifold.

And here is a closeup before I installed the lines.

It is a high pressure shutdown for the compressor and is in the 1996 EVTM.

Thanks, Bill.  That's interesting as Huck, the 1990 half-truck, didn't have that switch nor is there a place for it.  The A/C seems to work fine w/o it, so I guess I'll continue to use it this way.

I am changing to a FS6 compressor and cant get a solid answer on how much oil goes in compressor. It came with a label that it shipped with 3 oz. of pag 46 oil.

I suspect that part of the problem is that you "are changing to an FS6 compressor" so it isn't the original unit in the system.  But, I think we can figure it out.

I don't have this section scanned in but will.  However, I'll try to type in these snippets from the 1985 factory shop manual section on the FS6 Compressor And Clutch:

When it is necessary to replace a component of the refrigerant system, the procedures here must be followed to assure that the total oil charge in the system is correct after the new part is installed.  When the compressor is operated oil gradually leaves the compressor and is circulated through the system with the refrigerant.  Eventually a balanced condition is reached in which a certain amount of oil is retained in the compressor and a certain amount is continually circulated.  If a component is removed after the system has been operated a certain amount of oil will go with it.  To maintain the original total oil charge it is necessary to compensate for this by replacing the oil in the new replacement part.

A new service replacement FS6 compressor contains 10 fluid ounces of the specified refrigerant oil. Prior to installing the replacement compressor, drain four fluid ounces of refrigerant from the compressor. This will maintain the total system oil charge within the specified limits.

So they want the FS6 to have 6 ounces in it, and yours has 3.  I think you need to add 3.

Thank You Gary.

Gary Lewis wrote

I suspect that part of the problem is that you "are changing to an FS6 compressor" so it isn't the original unit in the system.  But, I think we can figure it out.

I don't have this section scanned in but will.  However, I'll try to type in these snippets from the 1985 factory shop manual section on the FS6 Compressor And Clutch:

When it is necessary to replace a component of the refrigerant system, the procedures here must be followed to assure that the total oil charge in the system is correct after the new part is installed.  When the compressor is operated oil gradually leaves the compressor and is circulated through the system with the refrigerant.  Eventually a balanced condition is reached in which a certain amount of oil is retained in the compressor and a certain amount is continually circulated.  If a component is removed after the system has been operated a certain amount of oil will go with it.  To maintain the original total oil charge it is necessary to compensate for this by replacing the oil in the new replacement part.

A new service replacement FS6 compressor contains 10 fluid ounces of the specified refrigerant oil. Prior to installing the replacement compressor, drain four fluid ounces of refrigerant from the compressor. This will maintain the total system oil charge within the specified limits.

So they want the FS6 to have 6 ounces in it, and yours has 3.  I think you need to add 3.

Hold on there!
They want 10 and pour out 4oz becasue that is what is in the rest of the system, hoses, dryer, evap coil and condenser.
What if you are installing all new parts or flushed out the old parts (evap, condenser & hoses) (but new dryer) then what do you add? How much oil is in the dryer or other parts replaced?

I just redid my system and I flushed out the hoses and condenser (they were about a year old) but installed a new compressor, evap coil & dryer so I added a full 10 oz to the system.
IIRC they wanted you to add some, dont remember how much now but can look it up, to the compressor (add some and rotate and add more rotate etc.) and the rest to the system in a way the compressor would not get a slug of oil.
They did not want it added to the dryer so think I added to to the evap coil after the dryer so it would have time to even out through the coil before getting to the compressor.

So far knock on wood my system is cooling pretty good but have not used the truck much since I did this last fix (I hope for good) but my son had to use the truck over the weekend when I was away and said it was blowing cold so I am happy with that.

So something to think about when adding oil to the AC system.
Dave ----

I'll see if I can get the rest of that section scanned soon.  However it'll go where the section from the 1981 FSM is: Documentation/HVAC/HVAC Systems.  You might look at the instructions on the section there.

Thank you Gary that would work for a 81 F100 with a York compressor but I am running the later FS6 compressor.

Also when I bought mine it had a paper & sticker that they come in 3 different ways.
1- fully filled with the right oil
2- half full with the right oil
3- filled with shipping oil that all of it needs to be drained and refilled with the right type & amount of oil.
IIRC the paper listed the amount of oil needed to fill the compressor.

To drain it you had to pull the shipping plugs and turn it upside down to drain it.
When it stopped dripping you needed to turn the crank to get the next chamber to drain.
You keep doing this till no more drops come out.

When filling you poured in a little and turned the crank then a little more and turn and more ... till the amount they wanted in was in. Thing was not to pour in to much as to hydro lock the compressor when it first started.
I need to find that paper
Dave ----

I'll see if I can get the '85 FSM section scanned as it has the FS6 in it.

15585.pdf

Here's that ranger schematic.

I hope I'm not getting out of sequence here as I have not fully read the thread. I'm just reading a little to wind down from a ten-hour drive. anyway, the systems did not need a high-pressure switch for very many years but then things changed. we retro fit but we are compromising! the fs10 is far more efficient than the fs6 all while using a refrigerant that will happily spike in pressure.  that said there is likely an operational reason for the pressure spike. low air flow across the condenser being extremely common. most often from a failing fan clutch. another common issue is a clogged orifice tube from debris coming out of an old condenser/compressor. another is as simple as air in the system (non-condensable) easily introduced into a clean system by the gauges themselves from going from one step to the other. I set up all at once so to maintain the seal between the vac pump, 134a bottle and vehicle. this does require a couple extra hoses.