Well you need to make sure vacuum is making it inside to the control.
Next time it happens start tracing from the motor on to the inside control.
Also have you pulled the blower motor and cleaned all the crap out? If not the resister gets hot and could catch fire and burn the car to the ground.
Let us know when you find.
Dave ----

 

 

 

If your switch is cycling the compressor too much and it's cold outside, this is normal. That is a low pressure switch. All that cold air moving through the evaporator lowers the pressure in the system, and it will cut it off before it freezes up.

Now, if it does it in the summer when it's hot outside, then you are low on charge. You are not really going to be able to zero in on this till the weather is above 70 outside. As the air gets warmer, it should cycle less. Some of the factory manuals have a chart with cycle times and ambient temperatures. You still may be low on charge now, and that can be causing the excessive cycling, but I would wait till it gets hot outside before trying to top it off.

Another thing you can keep an eye on: You can test it as is through the winter, if the cycling gets worse or it just quits working all together, then you know you have a leak and are definitely low on charge. But I still would not fool with it until warmer weather.

 

Yeah, get rid of the jumper wire!

The rapid cycling you had previously experienced is most likely due to a low refrigerant charge. For an R134a conversion, a good rule of thumb is fill by volume to about 80% of the specs for R12.

For now, ignore any pressure gauge readings. Your low side reading tells us the compressor is working fine, but that's about all I like to infer from the gauges. Some pros can interpret the required volume by reading pressure, but it's more of a dark art. For accuracy, I think you have to sacrifice a chicken and recite a mantra inscribed on an ancient scroll. For us mere mortals, the easiest method is to do a full evacuation and then refill by volume. That way you know exactly what you've got. The way pressure behaves with refrigerant is really weird. You can buy those top-off kits with a little gauge with a green band and it seems like that is all you need to know, but it's not so. Refrigerant under pressure behaves totally different from "normal" compressed gas, such as the air you put in your tires. All I'm trying to get at is don't place too much value in the gauge readings, and certainly don't use them to determine refrigerant volume, which is what you really need to know.

Working from potentially faulty memory, another possible cause is icing inside the system. When I evacuate an AC system, I like to put it under vacuum for hours, overnight if possible. This give us amateurs a big advantage over a professional shop operating under time constraints, who might only draw a vacuum for 30 minutes or so.

Back to the refrigerant currently in your system, I'd highly suggest doing a leak check before the evac/refill. Since you had filled the system not too long ago, and the present behavior suggests a low volume of refrigerant, you may have a pretty good leak. I've got an R134a sniffer that set me back only about $25 and it works great. Don't forget to check the evaporator, too. To do this, let the vehicle sit several hours, preferably overnight, and without turning on anything, check the discharge vents in the dash. If the evaporator is leaking, that is where the refrigerant will go. Remember, don't run the fan or that will blow out any accumulated refrigerant and the sniffer won't detect anything.

Once you know you have the correct amount of refrigerant in the system, you can then play around with the setting for the cycling switch on the receiver/dryer. It needs to be tweaked a little for R134a, but I'm having a brain fart remembering if it needs to go up or down. Perhaps somebody more knowledgeable can chime in. The exact pressure value itself isn't so critical. Basically, if the evaporator ices over, and the refrigerant volume is good (note I keep harping on refrigerant volume), bump up the pressure adjustment slightly and see what happens. If the ice stops accumulating, you're good. It's a little bit of trial and error. You won't hurt anything. Go too high and you just lose some cooling capacity. Go too low and it's as if you had bypassed the switch with a jumper...

One last thing: Make sure the exterior of the evaporator is clean. All airflow goes through there after the fan. Expect to find the face covered in leaves, pine needles, small rodent nests, etc. You can split the case for cleaning without having to remove the evaporator or break any connections. I think there's one bolt that comes in from the passenger footwell, otherwise all fasteners are easy to access.

 

 

I don't have that info for these Fords, but if someone does they will need to know the year of the truck and if it has factory air or dealer added air. I am assuming from your description it' factory, but asking to make sure.

 

 

Does it still use the 86 condenser?
I ask because the replacements you get now days you have to "tweak" to fit and is a little larger as it is for the newer trucks running 134a.
Even running the serpentine belt would the compressor make/model be different? I would think it is only the clutch & pulley for belt type would change?
I say this because on the 300 six motors they went to the FS6 compressor around 83 or 84 and yours being an 86 I would think would be the same.

I will see if the sticker on the radiator support on my 81 (300 six) has how much it takes (it had a York compressor small condenser) and see of the cheap Hanes book list anything.
I am working on getting my AC system together and will be using the FS6 compressor with V belt and large condenser so I would like to know the answer also.
Dave ----

 

From 1986 F150.

 

The sticker on my 81 F100 with York compressor did not take picture well but it said 3 lb / 12 oz of R-12.
The 86 I think would have the newer compressor so I wonder if that is why less oz?
Dave ----

 

It does. I think yours has a crankshaft while the later units have the wobble shaft.

 

Yes crank shaft with rod & piston and why it shakes so much.
Because of the 2 different types of compressor is why I posted mine had a York, I will be going with the newer type also.
Dave ----

 

​​​​​My '84 has the Sanden (barrel-shaped) compressor. The sticker (and the manual) specify 48 ounces (+/-4) of R12. Applying the 80% factor, I used 40 ounces for the R134a conversion and that has worked very well.

I hope I haven't scared off anybody by discussing how much refrigerant to use. It doesn't have to be hair-splittingly precise. The only thing I wanted to get across is that the pressure gauge doesn't correlate to quantity. Remember, refrigerant under pressure behaves very differently than "normal" gasses like the compressed air in your tires.