hello, forum. I have a 1988 ford f150, 4,9L that came with no AC from the factory. I have done many hours of research on doing a ac conversion. I have picked a blower motor ac assembly from a 87' truck as i have the 87-88 ac wiring (they changed designs 89-so on) and i got everything bolted on just fine. I bought a whole ac system fresh from rock auto. brand new lines, compressor, evap core, condenser. (most from Four Seaons) (reman compressor from r&y compressors) converted to r134a, Everything is put together. .
fist compressor i got remanufactured ended up being bad because someone used it before and the clutch plate was wobbly and did metal to metal contact, i returned it and got a brand new one and it sounds and works perfect. Pulled a vacuum for 30 minutes and it held for a hour. without moving. so i put 18oz of r134a in my system, and I read very high pressures from the low side. 110 when the truck is off, and high pressure i read none. when the compressor is on and running, i read 40psi. After the truck is turned off i get a hiss noise near the accumulator and liquid line. like the pressure is building up very high causing the sound. from the first bad compressor i got i also the same pressure issue, and i thought it was my compressor (and also it was wobbling. it was bad ) and now with the new one its the same problem. My brother had a extra accumulator (the one im using right now) sitting for a year capped and had vacuum on it, so i used it. it has rust around the threads of it, and i used it with the first run with the bad compressor. i had the first compressor removed but i kept the accumulator because i didn't even run the bad compressor for 5 minutes before not running it again and removing the bad compressor. I cant figure out what my problem to my high low pressure and no to low pressure on my high side. I had installed a brand new blue office tube that came with the Four Seasons evap core. Could the Accumulator be bad and causing the improper readings for the low and high side? this is my second time using it but i thought it would be fine as i didnt run the ac system longer then 5 minutes with the bad compressor. could my orfice tube be bad even though its brand new? (blue orfice tube). And also why does my system hiss after my car is turned off when the system stops running? i only put a 18oz can of r134a in the system and that isnt even enough for the system to be full. and its reading really high. Does anyone know any information or help to fix this? Thank you for reading. and helping.-james

 

What condenser? You need RED orifice tube, did you install it with arrow pointing into evap? 11oz oil. 38oz gas.

Fan clutch junk? Make sure have shroud and if possible upgrade to seven blade fan.

 

My 91's (low side) pressure is really high with the truck off, and I get the same hissing, pretty sure thats just the refrigerant settling. I can record it tomorrow if you'd like.

 

i have read up and ive just found that yes r134a has a red orfice while r12 is supposed to use blue, but there is also many people who also used the blue orfice tube for r134a because its the same exact size as the red one.
and yes i pointed the orfice tube correctly.

is it really 110oz of pag 46 oil?? that sounds like to much and 38oz sounds like overcharging ? is it really that much to work my system? by brothers truck is a 1997 f250 hd with a 5.8 and i did the ac on that one and i put 9oz of oil and 34 oz of refrigerant and that overfilled it.
ill look into the fan clutch and seven blade. i dont have a ac shroud yet i havent found one from the junkyard yet but i will look for that next.

 

Yes please a video would be very helpful. thank you

 

38oz is factory 134A fill. Red tube is diff orifice diameter than blue, they are not the same. 11oz oil is updated charge, it was less previously. The TSB has been posted here.

What condenser are you using? Pic?

 

Ambient temperature: 70f


Psi engine off

Psi engine running

https://photos.app.goo.gl/4umFoovfj6fcFze5A

My AC is going to be a bit different than yours, as it's an old r12 system stuffed with r152a. However the idea is similar enough.

 

What is a TSB?
im using a condenser from rock auto called spectra premium under the addition corrosion protection section of the condensers.
i dont have a picture but i will try to take one tonight.
on my brothers truck i bought a red orfice tube from UAC and matched it to my blue one before i installed both of them and i they look exactly the same. I read a post saying that it doesnt matter if some of them are the same size. but that was probably bs. Should i change it to a red orfice tube?
today i ran my truck with the 18oz of freon and 7and a half oz of oil and it runs and cools okay. its a little colder then outside but still to hot to have the windows closed.( i live in florida humidity is a bitch) the compressor would run for a little then it will turn on and off very quickly like the low pressure sensor shuts it off and turns it on repeatedly super quickly, on, off , on, off. so i dont think its good for the system to do that. why could it be doing that?

 

Thank you for the video.

this is my reading from with the engine off. temp outside was 85-90 degrees.

this is with the compressor picking up and running

 

I have just posted my readings of my gauges under junktownbill99s post.
i have pictures there posted if you would like to see them. could you let me know if those are proper readings? is there something wrong in those readings?
I only have 18oz of 134a and 7.5 ounces of pag oil in the system which could maybe be why the pressure is so high?
my compressor will turn on for a while, and then it will continuously turn on and off.
Should i put more refrigerant and oil in the system?
im afraid to add more because if i have to change a part theres no point putting 30$ worth of gas in the system for it to be removed.
thank you

 

What are you getting on the high side? To me, it looks like the low side pressure is too low and the constant cycling means that the system is undercharged.

 

On the tube, the colors mean they are different sizes and yes BS that they would be the same size and different colors
I dont think it really matters what color you have in there now as long as it cools.

The low side reading high when off is normal as the system has equalized. Why dont you have the high side gauge hooked up?
You would see that they both would read the same PSI after a while when off. The hissing you hear it the system equalizing.

The on & off of the compressor is because it is low on charge.
The low switch should have a psi on the side of the psi it works at.
If you watch the low gauge you see it drops and the compressor shut off. The system then starts to equalize and the switch closes turning the compressor on till it happens all over again. Put more charge in it and the compressor will stay running and the AC will start to cool.

BTW 134a runs at a higher psi than r12 did so you really cant go by the r12 readings when switching to 134a.
Dave ----

 

20psi is nearly same refrigerant temp. That is why short cycling...system is low as hell, not even half charged. System off always high when ambients high. Basic pressure versus temperature...physics 101.

Suggest getting an EPA 609 or take the truck somewhere to someone that actually knows what they are doing.

Multiple folks have told you what to do and what you need, yet you keep dismissing us. Good luck, I am done.

 

Should be 45-55 psi at 90°F but his gauge is only at 20psi.

 

Thank you i just charged my system and getting 45-55psi at 90 degrees out. Thank you for helping
its now cooling better.