Hi all,
First post here. I recently picked up a 94 f150 4.9L and the ac does not work. I did a little research on line and decide to jumper out the Lowe pressure switch to see if the compressor would engage, and it did. So I thought I found my problem, low freon. I went and bought some freon, attached it started the engine and turned on the ac, the compressor still would not engage but I thought once I added freon it would. Well the system didn't seem to take any of the freon and the clutch never engaged. So I tried by passing the low pressure switch and then add the freon while the clutch was engaged, still would not take the freon.
Is it possible the lp switch is bad and my system is fully charged? I suppose I could try to run the system by passing the switch to see if cold air blows but I read that if the system is low in freon and you run the compressor you could damage the compressor.

Any ideas?

Thanks!

 

You need to check the system for leaks, and I don't see you mentioning it, but you need to evacuate all the air from the system prior to filling it with freon, this requires using a good automated vacuum pump and gauges, and the system also requires the proper oil for freon equipped systems. You can check all the connections visually, if you see any crud it probably leaked at that spot and some oil scaped, then the dirt from the road stuck to it. There are also some leaks which you won't find without specialized equipment... If you aren't familiar with A/C systems and operation I would advice taking it to a shop at least for the lubbing/refilling procedure, that's what I did, installed all-new parts, then took it to the shop.

Btw, welcome to FTE! and to our Chapter.

 

as Encho said, you can not add freon until you have someplace to put it. you need to run a vacuum pump on the system to evacuate it before putting freon back in.
once vacuum is drawn, turn the pump and gauge manifold valves off and wait 1/2 hour to see if you loose any vacuum. if you do, you have a leak that needs to be found and fixed before you can charge the system.

 

I think the problem may be the hose that came with the freon attached to the can I can spray freon through it. Attached only to the truck, it does not allow the freon to escape. If I use a small screw driver on the truck I can press the button to release freon. Going back to the store to talk to them.

 

you problem is you do not know what you are doing.
if the compressor is not running, it will not take freon. if there is not enough freon in the system to close the switch, you will need to put a vacuum pump on it, recover what is in there, and evacuate the system before putting the freon charge in it.

 

You are correct. I don't know what I'm doing which is why I have come to a forum to ask those more knowledgable on the subject. If I knew what I was doing would I have come here to ask?

 

My advice? Take it to a pro a just accept the charge. A/C is NOT something to deal with if you don't know how to do it. Its obvious there is a leak somewhere in the system. You need that fixed and then have toe system fully evacuated before you can add new freon. We aren't trying to be rude, it is just the simple fact that there are some things on these trucks better left to the pros.

 

Not only Pros, but people equipped with the right tools. Nobody is being rude, we just don't want to see you damaging you A/C system just for saving a few bucks. That's why I suggested having the system serviced at a shop.

 

Just an update, I still don't know what I;m doing but,
I went back and exchanged the can of Freon, same result. the I read the fine print, you need to rotate the can 45 degrees, back and forth. So I did this in the paring lot. Someone walking out of the store saw what i was doing and told me if the compressor was not locked in, the system would not take freon, so I bypassed the low pressure switch and the system did take the whole can, blew cold air so I thought all was good. When I shut the truck off, I heard a biunch of hissing. I removed the jumper, started the truck and the compressor did not engage. SO i figured all the freon leaked out.
Two days later, I'm driving the truck and decide for the ell of it, to turn on the ac, to my surprise, it wsa blowing cold air. When I got home, the compressor was locking in and all was working. Four days later, its still working...how long this will last I dont know!

 

it will last until the freon leaks back out. could be a day, could be a year.
my crown vic has a very small leak in it, i have to recover what in left, evacuate it and recharge every other year.

for the size of the leak, i don't feel it is worth fixing.

if it had to be done every 6 months, it would be fixed though.

 

There isn't any major leak apparently, the hissing sound come from the compressed gas expanding in the system when you turn it off, so don't worry about it. Keep making visual inspections of the connections every now and then, but I think you're set if you're satisfied with you current A/C.

 

here is a hint, If it needed to have Refrigerant added to run at all, then it had a leak, i could be a small leak, but it has a leak.

I love reading threads like this, they make me chuckle.

Matt

 

I realize I have a leak of some sort. The entire point of adding to the system was to see how long it would last. I don't plan on doubling my investment in the truck to get the ac checked out and repaired. So if it last a day or two years, I can determine whether its worth it to add another twenty dollar can. If I happen to see where the leak is, great. Really, if it makes it throw the Georgia summer, I'm happy!
I do have another question, I realiz ac system seemed to be taxed when you accelerate hard. It's much more exaggerated on this truck. Whether the ac was working or not, Iif had the switch on max ac, any acceleration causes the vents to stop blowing completely. Once I let of the gas, the air comes back to the vents. Is this normal for this age of truck?

 

that means you have a vacuum leak somewhere. default setting on these truck when you loose vacuum is to switch everything to the defrosters.

 

well it sound like you need to start learning about your ac system. its not rocket science. 94 and you bought freon so i guess its a r134 system. just use it and eventually youll find where its leaking. if you had a vacuum pump youd be able to check the system for leaks but i assume you dont have one and there not cheap. im in airzona so ac is pretty important and the local shops here know that so they sock it to you, thats why i learned about it.