Well, it seems my A/C is not fuctioning properly. Basically if I start the truck up cold, the A/C works very well within a minute or so. After running the truck for 20-30 minutes, it blows warm air. It does this in any A/C / blower setting. If I shut the truck down for 30 minutes, the A/C blows cold again...

I figured the system needed a little charge, so I bought a charging kit from the loacl autoparts store. When I hooked up to what I think is the low side port, the gauge reads high and now I have a few questions...

For a 1997 F150, 4.6L there are two visible ports. My assumption is that the low side port is smaller than the high side port. It appears the high side port is inline with one of the coolant tubes while the low side port is located on the side of the "can" (forgive me for lack of proper terminology). Are these correct assumptions?

Assuming that the above is correct, what could make the system shut down after 20-30 minutes and why would I have high pressure on the low pressure side??

Thanks in advance

 

Hi,
My 97 F-150 has been doing the same thing for almost a year now. Sometimes it will work fine for an hour or two and other times it only works for about 15 min. I have noticed that the clutch stops turning after it starts blowing warm. It took a while to see that the clutch stops because every time it started blowing warm I tried to pull over and check but for the longest time it would start working again before I could pop the hood. Now it stops for a longer period before it starts back up again. I did have ford check it out twice but they can't seem to get it to fail when they have it and all presures seem to be OK. Someone thought it might be the clutch but I am not sure.

If you find out anything PLEASE post and let me know. I will do he same if I find out anything.

Ron

 

ok I am very rusty on the nomenclatures but inside the cooling element where the air flows through is a device that measures the amount of or how cold the air is and when that goes bad that will cause the problem you are having. Darn and I used to be certified on this junk. When I get home tonight I can look up the name for you so you can change it. I am not sure how hard it is to change on a ford but it is located inside the cab. Unless anybody else has the name. It is a reducer type part.

Lance

 

Would that be the Blend Door? I don't think that is my problem because I seen that the compresor stoped.

 

negative, a quick llok on the inranet and thereit is I believe the problem is the Orifice tube. The way it operates It could cause this problem.

Lance

 

The orifice tube??? That's a new one to me. Do you know where it is and what it looks like or what it does?

Thanks

 

Yes the orifice tube is lodcated in the cab in the cooler radiator. It's job is to regulate how cold the cab area gets. When it does not work well or is faulty it gives false readings to shut the ac system down. I would have to look it all up at home and paste it in to give you the way it works this is in laymans terms. Yes you can do it your self.

Lance

 

From what I have seen in searching orifice tube does this mean I have compresor problems that would have caused it to clog? Does the system need to be evacuated to change the orifice tube? Also I did notice that the compresor stoped the one time that I had a failure. Woulde the orifice tube tell the compresor to shut off?

Thanks,

Ron

 

yes, it would tell the compressor to stop, or the compressor would run all the time and freeze you out. Sometimes the orifice tubes just get or go bad. You deffinatly want to evacuate the system then use the machine to evacuate the air out of the system and refill. all your compressor does is circulate the coolant from the low to high side so as long as it works there is nothing wrong with it. But I beleive the accumalator could be going bad (I may have the name wrong) (the silver cylinder on the back fire wall) what it does is remove the water out of the system and any imputities that may get in there. If it stops working then the orifice tube could clog. So you may want to look into changing that as well. ( if it were my vehicle I would) Alwasy remember once you crack open the system you must use the special machine to refill the system it evacuates all air and every thing from the system, then holds it for about 5 to 10 mins this is to see if there are any leaks if it fails then there is a leak somewhere in the system and must be repaired before filling. Once that test passes then the machine fills the system to the required specs which is imput before the operation begins. Takes about 20 to 30 min for the whole process as long all is ok. If there is a leak then can put a special dye in the system to find the leak where ever the leak is it will come out either green or red normally a green color.

Lance

 

Thanks, I will look in to the orifice tube. Your help is greatly appriciated.

Ron

 

Forget (for now) looking at the oriface tube.

Both of you, go look at your compressor clutch.

It it stops turning, the system quits operating and the pressures on both the low and high side equalize to a point that depends on the underhood temp. A fully charged system may show this static pressure at anywhere from 70 to over 100 psi.

Don't know how prevalent it is on the F150 compressor clutches, but on the SHO, this is a sign that the clutch is wearing. It can often be fixed for a long time by adjusting the clutch gap. This is done by removing the clutch disk and removing shims to bring the gap back into operation range. A weak clutch will often engage (temporarily) if you tap or nudge it with something like a bromstick, etc.

The function of the oriface tube is to act like a dam on a river. It holds back a large charge of refrigerant just like a dam does, allowing a metered amount of refrigerant into the evaporator core just as a Tainter gate on a dam would allow a dam operator to control water flow past (through) a dam. Typical failures of an oriface tube would be for it to either clog or to increase in size. Either failure would be recognizable from HIGH-LOW pressure readings. The oriface tube never tells the comnpressor (or anything else) what to do. It either does it's job of metering refrigerant or it doesn't.

Steve

 

OK Guess you know what you are talking about, I agree on the clutch to check. but I have been where the orfice tube had to be changed as well because of going bad. on the systems I have worked on it is a common part to go bad especially if the system is opened and run with a leak allowing junk to get into the system. When I was trained on the system it worked the way I said, So what you are sying is I was taught wrong. any thing is possible, also I never did much work on them since my training because I was stationed in Belguim (the country) in NATO and it never got hot enough there to use AC. So I guess I learned something.

Lance

 

my 97 does the same thing...just had it professoinally filled...was a tad low but it still on and off. Will remove shims. My clutch bangs all the time too when the air or heat is on...drives me nut!!!

thx

Bob

 

Steve, Thanks for the post. I removed to clutch and only had one shim. (checked all inside and out) I have had this truck since new so it must have come from the factory with only one. When I remove the shim it seems to be to tight, so I found a washer that fit that was a little bit thiner and it seems to work better but when I run at about 2500 to 3000 RPM's it doesn't seem to engage. I think I am on the right track but I just need a thiner shim. Does this sound about right?

Thanks,

Ron

 

Sanded down washer to make it a little thiner 0.040 or so in thickness and all seems to be working fine now. Have 0.023 in gap between clutch face and pulley. (book says between 0.018-0.030) Even when I turn on the AC while reving to 3000 RPM's it run OK.

Thanks guy's

Ron