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Hi,
I have a 1987 c class motor home with a E-350 van front. The issue I have is twofold. First, there is no low pressure switch anywhere to be found. None on the dryer or low side line that I can see. Next is this is a R-134a retrofit. So the compressor runs whenever ac is on and doesn’t cycle off. Also, I’ve read that the proper amount to fill it to is the R-12 amount x .9 then subtract .25 lbs. I can’t find out what is the recommended amount to fill it with? Also, how much refrigerant oil should be in the whole system?
thx
bruce
All of the information I have would be from a ford service manual and "may not apply" to your motor home if it has a dealer of conversion installed ac system.
you may have one of two different types of switches that control the compressor. Ford calls them de-icing switches. one operates like a thermostat while the other does operate off of pressure in the system.
Here is the one that operates similar to a thermostat.
It looks like this and the tube is inserted inside the evaporator core. When the evaporator reaches 25F, the switch opens the contacts and the compressor shuts off. To test it, mix up a solution of ice water and salt. insert the capillary tube into the solution. Use a test light or meter and when the temperature reaches 25F, the switch should open. Something i have never checked is to see if there is an adjustment on the switch. I do not know if this type of de-icing switch needs to be replaced when you convert to R134a or not. When converting a system that uses the pressure type switch, there are 2 switches listed. one for r12 and one foe R134a. The pressure switch is also adjustable though.
Here is what the thermostatic de-icing switch might look like
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here is what the pressure type deicing switch looks like also known as clutch cycling switch.
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and it screws on top of the accumulator. the fitting on the accumulator looks like a schrader valve.
Thx for the reply. I believe that I have the factory installed AC because it has the dryer without the port for the low pressure switch. I’ll check the hvac housing when its light out (4:45 right now) but that makes sense. It appears that whoever converted this to r-134a, overfilled it with refrigerant oil as well. I evacuated the system and out come over 8 ounces of oil! I’m sure that there’s a lot more in there so I ordered a new dryer and will flush the condenser and evaporator core before attempting to refill it. I have a seal kit so it will be a good time to get rid of the old seals as well. A question I have is does the thermostat type cycling switch go to a relay or just open up the circuit for the clutch directly?
thx
Bruce
power comes from the selector switch to the thermostat type cycling switch and then straight to the compressor clutch. it is the same if you have a pressure type switch.
Since its a conversion, nothing is gonna match the original R-12 stuff if it was done right. (sounds like it wasn't and a low pressure switch was not installed on the new dryer, if the dryer was replaced like it should have been).
I won't guess on oil.
Take a best guess at refrigerant filling. Put a fan on high in front of the radiator and adjust the fill until the vent output is at its coldest, or around 30° less than ambient outside.
I had the exact same Motorhome setup, 26' Jayco. Loved that 460 engine. I had refrigerant leaks I never could track down on my dash AC. It would last 2 days max so I didn't bother using it as it was when R12 got so dang expensive. (On one of my '89 E-150s I used an R-134/propane combo in the R12 setup that worked pretty good) I just used the overhead AC and a fan blowing it down to my feet since that wheelwell gets so dang hot. Had double insulation on the doghouse cover too. Still was too hot. Thank God for cruise control.
Thx for the reply and info. One more question if I can? From what I gather, the clutch cycling thermostat comes preset at 25 degrees f. Does it have an adjustment so I can raise that a little to let’s say, 30 degrees? I’m thinking that r134a won’t get the evaporator core as cold as r12 in a retrofit system. If true, then the switch won’t cycle, opening up the clutch. What I’m trying to avoid is the compressor running nonstop.
Thx
Bruce
I personally don't know about the one that operates like a thermostat. if it is not adjustable then perhaps they a company like 4-seasons sells one that is designed for R134a.
the pressure type switches are adjustable but i do not know if the cut in and cut out differential is the same for R12 and R134a.. I know thye sell a pressure switch that is preset for r134a..
