AC - 134a conversion questions...

[AcIdBuRn02ZTS]

Hey guys...

So my '90 F350 came to me missing most of the AC components. I have since swapped to a '93 engine with serpentine setup... ordered new hoses, condenser, evap, drier, orifice tube, etc.. all new. Only thing that may get reused is the compressor that is on the engine now... not sure of its condition but I hate to replace it with aftermarket crap if the OEM unit is in good shape...

Don't have the specs for what pag oil should be used and how much, by weight, of R134a I will need.

Does anyone have those specs?

So looking forward to having AC again!

 

[Grady J]

just reluctantly completed my 134a retrofit last weekend, spec calls for 10 oz of oil (i used ester oil) and 52 oz refrigerant. I was surprised to see that after only two 12 oz cans my pressures were perfect and ac was blowing ice cold air.

 

[franklin2]

If you do not clean out the old compressor of all the old r12 oil, you should use ester like the other poster. The ester does not react with the old r12 oil like pag oil does.

Go to Walmart and buy the conversion kit. Stick it in there and drive on, it has the refrigerant and the oil already in it. Just make sure you pull a vacuum on it for at least a couple of hours.

 

[AcIdBuRn02ZTS]

Yup. I've done a few ac jobs... I'll pull it down for a good bit. Was considering flushing the compressor but there is no way to get ALL of the oil out of it. I need the fittings anyways so I'll order a kit.

Did you end up using all 52oz or did you stop at 24?

 

[AcIdBuRn02ZTS]

Here is what I dont understand...

In 1990, it calls for 52oz of R12..

In 91-93 calls for 44 of r12

94 calls for 32oz of 134a

All of those body styles use the same components.. same evap.. same condenser... similar lines.. and similar compressors...

Im guessing 134a doesnt require nearly as much charge as r12 does which would make sense in your case (24oz and blowing cold).

 

[needlenose]

...Was considering flushing the compressor but there is no way to get ALL of the oil out of it....

I was always told to never do this. Something about you never get enough oil back into the bearings. The flush flows much better than the oil will and you have to take a lot of time and repositioning to get all surfaces re-coated(hopefully).

That's just what I have been told several times by different technicians.

 

[gnathv]

94 is different condenser, evaporator, accumulator and hoses. Not sure on compressor.

 

[Shawn MacAnanny]

94 is different condenser, evaporator, accumulator and hoses. Not sure on compressor.

Compressor is the same style and from what I remember the lines were the same other than the fittings (I used a conversion kit). The condenser was bigger. The pressure switch was different and dryer looked the same to me

I converted my 93 to 134 with a new compressor (old one was dead) new pressure switch , flushed everything with denatured alcohol and put in a new dryer and orifice.

 

[gnathv]

Other than the fittings means different lines.

 

[Shawn MacAnanny]

Yeah but you can buy a $7 kit to convert the fittings so the lines can be reused for conversion

Interdynamics VA-LH8 Air Conditioning Conversion Adapter Kit with 2 Adapters - Pack of 1 https://www.amazon.com/dp/B000CO7QLK/ref=cm_sw_r_cp_api_eW0pzb71PYWWX

 

[Shawn MacAnanny]

Here is what I dont understand...

In 1990, it calls for 52oz of R12..

In 91-93 calls for 44 of r12

94 calls for 32oz of 134a

All of those body styles use the same components.. same evap.. same condenser... similar lines.. and similar compressors...

Im guessing 134a doesnt require nearly as much charge as r12 does which would make sense in your case (24oz and blowing cold).

R134 had a molecular weight of 102.03
R12s molecular weight is 120.9

84% of 44oz would be 37 ounces or r134 in the same space. Though the 134 condenser is larger so I would think it would take a litttle more than that.

 

[gnathv]

The original poster stated he wondered why a 1994 held less oz of 134. It's a different system. I'll agree you can convert a 12 to 134 but a 134 system hold less.

 

[AcIdBuRn02ZTS]

Actually... my main question was what would the spec be to refill my 90/93 system with r134 after replacing everything...

From what I'm reading, r134 requires roughly 80% of the r12 spec. I'll plan on ~3 12oz cans and go by the pressure and temp coming out of the dash when adding the 3rd.

Thanks for the input.

 

[chris142]

When switching from r12 to r134a putting in 85% of the r12 charge will usually work fine. My truck holds 3.25lbs of r12,I use 2.75 lbs of r134a.

 

[AcIdBuRn02ZTS]

Sounds about right. Thanks