I just bought this truck. 89 f250 with 90k mi, sweet deal. The Ac didnt work when I bought it. I changed out what I considered to be a leaking low side conversion nipple, Evacuated the system and recharged with 3.4 lbs of r 134a.
I am getting a high side of 300-350psi and a low side of 70-80 psi. I think this low side pressure is way high. the vent temps are 60 degrees at best with windows up on recirc going down the road.

Does anyone have any idea wht would cause the high low side pressure with such a hig side pressure? Dosent make sense to me. I think i have the charge right. I dont know what it is supposed to be but the conversion tag says 3.4 lbs so i was going off that.

Thanks
Jeremy

 

Well for one things you've got too much 134 in a R12 system. If i calls for 3.4lbs then start off w/ just below 3lbs of 134. Never charge as much 134 into an original R12 system. That should bring things down to normal.

 

Whoa!! That system only needs about 36-38 OUNCES of R134a. You''re WAY overcharged.
You need to recover the refrigerant and start over. Check to make sure the orifice tube didn't blast down into the evaporator inlet tube. That doesn't happen often, but it does happen. Causes all sorts of strange problems.

 

holy $%&, are you sure you read the tag right. take isrx's advise and maybe start a little lower on you charge. 34 oz. is the proper charge with r12.

 

I read the tag right. it says that whoever converted the sytem put in 3.4 lbs. This didnt sound to far off to me since my kenworth takes 3.5 lbs and has a much smaller cab area to cool.

I like the advice on the orfice tube. I have never had one apart and didnt know the tube is removable. I just figured it would be fixed. If it did blow down into the evap inlet can it be removed without removing the evap?
Anyhow makes sense I can see how this would cause a low side high pressure. I wondered about the orfice tube but just could not belive the orfice could get larger.

How do you get the orfice tube apart to see if it came apart.

I found on lmc truck parts they have the orfice tubes. there is a red and a green. What is the difference between them?

Will try more to follow
Jeremy

 

whoever converted the system put the wrong tag on it, and overcharged the system.
factory specs for R-12 is 3 lbs, or 48 ounces.
the proper charge for R-134A would be 80%.
2.4 lbs or 38.4 ounces.

 

Well, on the bright side, now would be a good time check for leaks with that much refrigerant in the system.

I'm with the other guys though, you have WAY too much refrigerant in your system.

 

Ya know I am starting to think I have to much refridgerant in the system LOL!!!

Ok i think we have established there is to much in the system LOL

How do I get the orfice tube apart???

If it did blow the orfice into the evap inlet like sugested earlier is it possible to get it out witout taking out the core???

The cans are 13 oz. I put three cans in which is 39 oz. This is close to what I am getting from everyone is a proper charge right? Ok even with this in the system it was still only pulling down to 70 psi on the low side. anyone have any explination for this?? I guess the orfice tube coming apart is the only thing that makes sense. If it did come apart the orfice would now be larger and allow more flow making it harder to pull a low pressure on the low side.
Thanks

Jeremy

 

What's the pressure on the high side? If it's over 200, you still have too much refrigerant. I'm not an expert on R134a, but I used to, a long time ago, work on a lot of medium/low temperature refrigeration systems. As far as pressures go, I think that R12 and R134a are pretty close. Typically, a system operating on R12 should have a low side pressure of about 30 psig and about 180 psig on the high side. With the kind of pressure differential you described initially, 300-350 high and 70-80 low, I don't think that you have a problem with your orfice tube. I would simply bleed some pressure out of the high side until you get your pressures down to right around 30 and 180.

 

"Ya know I am starting to think I have to much refridgerant in the system LOL!!!
Ok i think we have established there is to much in the system LOL"

Hmm, what ever gave you that idea?

"How do I get the orfice tube apart???"

The orifice tube is in the evaporator inlet pipe. It's the smaller tube with the liquid line from the condenser connected to it. Recover the refrigerant, disconnect the Evaporator inlet fitting and look in the tube. You should see it just below the connection. If it's farther than about 1/2 inch beyond the end of the tube, it's gotten forced too far in. You might be able to get it back out, but probably not. They usually break at that point. If you can't see it, it's down in the evaporator and it ain't coming back out.

"If it did blow the orfice into the evap inlet like sugested earlier is it possible to get it out witout taking out the core???"

See above.

"The cans are 13 oz. I put three cans in which is 39 oz."

Those cans are usually 12 ounces, 3 would be 36 ounces.Did you put 3.4 lbs (54ounces) in, 36 ounces, or 39 ounces? That makes a big difference.


"This is close to what I am getting from everyone is a proper charge right?"

Yep. 38 ounces is the starting point (These trucks usually perform best with closer to 40, but don't worry about that just now).

"Ok even with this in the system it was still only pulling down to 70 psi on the low side. anyone have any explination for this??"

If you only have 36 ounces in there, the low side should be much lower. The high side should be lower also. Those pressures could point to low airflow over the condenser.
If the system is actually overcharged, those pressures may be expected.

" I guess the orfice tube coming apart is the only thing that makes sense. If it did come apart the orfice would now be larger and allow more flow making it harder to pull a low pressure on the low side."

Maybe, but it all depends on how much refrigerant is in the system. Don't worry about the o-tube just yet.
First, answer these questions:
- How much refrigerant did you actually put into the system (in ounces).
-What is your ambient temp
-What are the pressure readings at that temp. 1500RPM, doors open, Max AC, and High blower.
I have a hunch. If you really only have 36-39 ounces of refrigerant in the system, mist water from a garden hose over the condenser. Let us know what happens to the pressures.

 

Ok I put in 4 cans total. The can I purchased from orielleys auto parts and they say 13 oz on the cans. When I was charging up the sytem I put in three cans to start. with three cans in the sytem at an ambeint temp of 95 degrees the low side pressure was 70 psi and high side of 300 psi. This is at about 1500 rpm set on max ac recirc windows up. at best I could only get 75 degrees at the ducts.
I then added the fourth can of freon. the low side pressure was still 70 psi with a high side pressure of 350 psi. same conditions.

Oh yea and yes I did evacuate the system before charging.

Ok so I thought maybee I needed better airflow over the condensor so I test drove the truck and at best could only get 60 degree at the vent.

I have not tried it but my guess will be that misting water across the condensor will only slightly improve the pressures. I will try it tonight if I get time though.

I dont belive that I have an airflow problem. the condensor core is clean and unresrticted. the fan clutch works great and with the fan on it blows tons of air to the point that you can see the temp gauge raise then fall with the thermastat cycling. thats pretty good for a 460 sitting still and not moving.

Thanks
Jeremy

 

You are at least 13 ounces overcharged then. Your pressures were too high with 3 cans (36 ounces) in the system, so there is another problem.

"First, answer these questions:
- How much refrigerant did you actually put into the system (in ounces).
-What is your ambient temp
-What are the pressure readings at that temp. 1500RPM, doors open, Max AC, and High blower."

You answered the first one. Now answer the other 2. The answers are important.

"I dont belive that I have an airflow problem. the condensor core is clean and unresrticted. the fan clutch works great and with the fan on it blows tons of air to the point that you can see the temp gauge raise then fall with the thermastat cycling. thats pretty good for a 460 sitting still and not moving."

This is a guess based on what you think you are seeing. Misting water on the condenser will either confirm or disprove this for sure, after recovering the excess 13 ounces of refrigerant. Doing this test with the system overcharged won't tell you anything.

 

Actually I did answer the other two questions.

with three cans in the sytem at an ambeint temp of 95 degrees the low side pressure was 70 psi and high side of 300 psi. This is at about 1500 rpm set on max ac recirc windows up.

Only thing different is I had the windows up doors closed not open.

It will be a while before I can get the system recovered and properly charged as i dont have the equipment.

man this is some good info though
thanks
Jeremy Dunn