I've got a 1997 F150 Lariat 4.6L 4X4.
I mistakenly discharged my system when I was doing a head gasket job, don't even ask how I did this.
I've got the truck running now and have added 3 cans of R12A (not sure if that's enough) but the clutch still won't engage unless we apply voltage directly to it, when this is done the A/C blows slightly cooler but is still warm air.
Does anyone know what the pressure should be pre and post clutch engagement?
Thanks
Bill

 

Why on earth are you using R12a in an R134a system?

"R12a is the popular name for a hydrocarbon refrigerant blend made up of a mixture of propane and butane. These blends are highly flammible and you assume some risk by using them but they do work very well in most applications. Do your own research and perform a good risk assessment on your car first before using one.Hydrocarbon refrigerant blends are heavily marketed as drop in replacements for r12 that claim to produce colder vent temps. In my experience this is not always the case. ....... In fact whenever you use a blend refrigerant the system should be disassembled inspected and all seals replaced other wise the leaks will affect the blend mix and cause more problems."


Did you also pull a 29.5" vacuum on the system before charging? Air in any AC system is a problem, but when using a flammable refrigerant...well!!

 

Thanks for your reply, when I researched the web and contacted the manufacturer they all stated that R12A and R134 were fully compatible and could be mixed, I didn't do a vaccum first so that may cause a problem but I did find a blown fuse and am about to see what happens now.
After doing an inplace head gasket job it wouldn't be a bad thing for it to go up, maybe I'll let my wife try it.

 

Pulling a vacuum is absolutely necessary before charging your AC. Air can drive up the High Side pressure and damage the compressor.
You didn't actually mix the 2 refrigerants (which is actually illegal in most places). I was just wondering why you're putting a shady, barely legal, highly flammable refrigerant into your truck when R134a is readily available and is the proper refrigerant for your system?
I see you're in Canada, and the regulations for refrigerants are different than in the US. But that doesn't change the fact that HC refrigerants are just a bad idea all around. Of course, the manufacturer will tell you it's the best thing since sliced bread. They have exceptional marketing departments.
Please be careful.

Oh yes, let the wife try it out first btw.

 

I replaced the fuse and things seem to be working OK, around here R12A is readily available everywhere but the only supply of R134 that I could find came in 30lb tanks (probably a bit more than I need).
Any idea where I can find out what the pressure readings should be, in the repair manual I have it just says the system capacity is 34oz's but no pressure readings.
Thanks

 

The charge capacity and pressures with HC refrigerants are different than with HCFC refrigerants. I'm not familiar with what they would be. See if the R12a website has a discussion forum, I believe it does. You can probably find the info there.

 

R12A is basically propane and will cool, but may explode in a front end collision.
You need to vacuum an empty system for two reasons, one is to boil out any moisture in the system. Moisture will freeze in the orifice tube and block the system. Two, to make sure there is no air in the system. This will throw the pressures off and can cause over pressurization issues.

Oh, and I moved this to the 97-03 F150 forum since it is not directly engine related.

 

Propane being dangerous as a refrigerant in autos seems to be a US only thing. Most other countries allow it and it's quite prevalent in places like Australia. I know a lot of people that topped off their R12 systems with propane as they started to phase R12 out. While it could explode if you had almost all of a properly charged system drain into the passenger cabin, an explosion of that small amount of propane is less likely to occur than a cell phone igniting gas fumes as you fill your vehicle, which mythbusters busted as a myth, yet like propane in car A/C systems, there are a lot of unconfirmed reports of both things happening.

It would be very difficult to get an isolated amount of propane to pool in an area of a cabin to explode. My knowledge doesn't come from having many vehicles with propane A/C systems (1) but from my family having a propane business from the late 60's to the late 80's.

A propane leak into the cabin is instantly recognized, whereas a leak of R134a into the passenger compartment can't be smelled, and only a small amount can cause testicular cancer.

BTW, I wonder how many computer users spraying their keyboards with those air spray cans realize they are spraying R-134a.

 

for a generic air conditioner system, the pressure on the hi and low side will be the same, about 80-100 psi when motor is off. When running, about 90 degree F outside, the low side will be 35-40 psi, and the high side will be around 200 psi. This just gives you an idea if you are in the ball park. Better numbers are available for specific ambient temps, and different freons.

 

Thanks for the pressure information, my neighbour had a gage the actually is colour coded to show when the system is in the proper ranges so that will help as well.
Bill

 

Bill, that gauge won't help whatsoever. They give you no real info and are notoriously inaccurate to boot. You really need to source a manifold gauge set.

 

I'll see if I can find a set, maybe Canadian Tire loans them since that's where I bought the R12a.