Hello, everyone!

I have a 1990 Ford F-250 diesel. I decided to convert the AC system to R134A. Here is what I did:

Replaced AC Accumulator
Replaced orifice tube with one for R134A
installed fittings for R134a on high and low side
Vacuumed system
Refilled system with 36 oz of R134A.
I jumped the accumulator plug as I was putting in the refrigerant - circulated the 134A

The air blew super cold when I charged it at idle, but after driving at highway speeds in 96-degree weather, it warmed up to almost no more cooling. I thought that maybe there was a leak and I lost all my refrigerant. HOWEVER, I went outside tonight (the weather is cooler), and the AC seemed to blow very cold at idle. It does not appear to have leaked any 134A.

I'm trying to figure out what I might have done wrong, here. Do I need a new compressor? A friend recently told me that maybe I needed to replace the compressor oil? I've done this conversion before on two other 1990 F-series pickups and they both worked without any issues.

I have run dye through the system and there does not appear to be a leak anywhere.

Can anyone give me any advice on what to check, here?

Thank you all!

Joe

Any advice would be greatly appreciated. Tomorrow is another scorcher!

 

Install manifold gauge set to monitor pressures on high and low. How is your fan clutch? How much r134a you charge your system to? On conversion from r12 to r134a, charge the system to 80% of max charge of r12. Is your condenser have debris in the fins? Sounds to me if all checks good, you got a weak compressor or the condenser is plugged, suggest replacement

 

Is the compressor not turning on? Is it getting over pressurized and shutting off?

Or is it overcharged and freezing the evaporator?

 

If it cools good at idle, but not at speed, that sounds like overcharged to me.

 

What are your system pressure at idle and 2500 rpm?

 

Hello, everyone!

Update with some more info:

When you ask about the fan clutch, are you referring to the compressor clutch? Or the fan on the crank? Would that make a difference?

I put 2.5 12-oz cans of R134A into it, so that should be around 30 oz.

When I hook my gauges up, my low side is off the charts both at idle and 2500 rpm -- The low side pegs the needle all the way around past 120 psi. However, it is very hot - (over 90 degrees out here) - and according to the gauges, I think that may be correct for R134a at temps over 90 degrees. The pressure on the low side stays pegged max at idle as well as at 2500 rpm.

The High Pressure side comes in around 220 psi, and creeps up just a little bit to about 230 psi when I bring it up to 2,500 rpm.

I replaced the orifice tube and condenser.

Does this help?

Correction - The AC is not super cool at idle speed . . . It seemed to be great and cool in the first few minutes of charging it, but after driving a few miles, it is pretty consistently medium cool. (I don't think anything leaked out - I have a few drops of dye and I used a black light and did not see any leaks)

The compressor seems to be running as it should - not cycling on and off. Is there a way to test whether or not I have a weak compressor?

Thank you all for any advice you can bestow. I appreciate it!

 

Here in Florida at 98F temps I get about 45psi on the low side with my 89 Converted to R134. Don't have a high side gauge to see what it is as.

Sounds to me you have a orifice tube problem, weak high side psi with HIGH low side PSI. Wrong tube or gotten damaged and not flowing the R134 correctly.

On my 89 F250, I converted it over 10 years ago, still with the old 89 R12 condenser and hoses! Blows ice cubes out execpt at idle it warms up a little due to the smaller condenser.

 

You cant get a full charge using cans. You need to use an AC machine with a decent set of gauges.

Also R134a is not as efficient as R12. Compound that with R134a in an R12 system and you will never get the same amount of temp change as a newer car with a system designed for R134a.

 

You have a restriction in the low side and you need to fix it. What orifice did you use?

 

IDK who told you that but that is not true.

 

If he had a restriction on the low side, he would be running vacuum on the low pressure gauge.

Quote:

When I hook my gauges up, my low side is off the charts both at idle and 2500 rpm -- The low side pegs the needle all the way around past 120 psi. However, it is very hot - (over 90 degrees out here) - and according to the gauges, I think that may be correct for R134a at temps over 90 degrees. The pressure on the low side stays pegged max at idle as well as at 2500 rpm.

There is NO WAY the air would ever be cold or even cool if your low side is reading 120psi. There is a pressure-temperature relationship. It's not exact, but the rule of thumb is psi = temp, so 120 psi would be 120F.

If your low side is at 120psi, your orifice tube is not doing anything, as in, it's missing.

 

Automotive Technology told me. Its also not legal to preform AC repairs unless you are certified and using an actual AC machine. The system needs to be under a vacuum before charging. You can get a lot in but not a full charge with cans.

 

Belt could be slipping or clutch could be going out. I would replace pressure cut off switch with a r-134a model. Also sounds like it could be overcharged.

 

You can buy DIY cans of freon at every auto parts store. Yes, it is illegal to discharge a full system into the atmosphere, but an already dead system can be fixed at home if you have the proper knowledge. I built a whole system in my vintage truck, vacuumed it with a Harbor freight air powered vacuum pump and a set of gauges and filled with a 30# bottle of 134a. Works great.


What is your schools theory on this?

 

Also sorry, my above comment was not meant to be snarky.