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The (hopefully) official R134a conversion thread

I arrived at my friend's house around 2:30 and we got started at 3. I left his place at 1:45am. We spent about two hours total running back and forth to Home Depot and Ace and getting dinner, but the rest of the time we were in the garage working.


Some quick hits on problems we ran into:
  • since the Sanden compressor is longer than the factory R4 setup, the line that goes to the condensor was too short so we had to cut the hard line and install a copper pipe extension with some compression fittings. I'm not 100% sure it will hold up long term so I'll be exploring getting a custom line cut
  • when reinstalling the serpentine belt, I did not have enough slack to route the belt according to factory specs. I had to eliminate the roller wheel between the A/C and crankshaft pulleys. I haven't noticed any slippage of the belt so i'm thinking it may be a non issue
  • the A/C cycling switch I bought at O'Reilly has a different electrical connection than the factory wiring, so I'll have to return it and determine whether or not I can find a R134 compatible cycling switch that works with my factory wiring, or if I'll need to buy a plug that fits and split it into my factory wiring. For now I have the plug jumped with a paperclip to allow the compressor to cycle because the R12 switch cuts off pressure around 46psi, which is about where my current low side pressure sits (ambient temp was approximately 85-90 degrees at 70% humidity)
The A/C works wonderfully now. I achieved 27.2 degress at the middle vent with the blower fan on low going down the highway at 65mph with ambient temps around 70-75 degrees, and this morning on the way to work I had the fan speed at the 3rd setting (2nd from high) and was seeing vent temps of approx 38 degrees with ambient temps of around 80 degrees.

The hardest part was trying to install the extension pipe inline with the compressor/condenser line. If the factory lines had been long enough, the project probably would've been reduced by at least 3-3.5 hours. Most of it was because we were just going very slow and having to make a couple of hardware store runs to get bolts to mount up the A/C compressor.
 
27.2 degrees is generally too cold. I suspect the pressure switch is set too low. The compressor should turn off before that.
The two problems with that low temp, is freezing of the evaporator which will block air flow, and worse than that is the possibility of liquid freon getting to the compressor which will destroy it real quick.
 
Fordum said:
27.2 degrees is generally too cold. I suspect the pressure switch is set too low. The compressor should turn off before that.
The two problems with that low temp, is freezing of the evaporator which will block air flow, and worse than that is the possibility of liquid freon getting to the compressor which will destroy it real quick.
Click to expand...

Do you think once I get the R134 cycling switch correctly installed it will prevent the issue you describe by cutting off the compressor? Or do you think I might have overcharged it? We went with a 134 pressure table and we left it at 45psi, even though the table said to shoot for 50-55psi based on our ambient conditions.
 
There are three basic ways an auto air conditioning system controls the temperature of the evaporator, and prevents liquid getting to the compressor.
Not all systems use the same method. Some of them use one, or more than one.

A thermostat with the sensing bulb inserted into the evaporator which cycles the compressor.
An expansion valve that regulates the flow of the freon into the evaporator.
And a pressure switch that cycles the compressor.

I have seen and worked on all three over the years. I'm pretty sure that yours uses an orifice instead of an expansion valve, and relies on the pressure switch for temp control of the evap.

If so, then putting in the right switch should cure it. In the meantime, be darn sure that you do not let liquid get to the compressor.
A few drops will snap the crank, cause it to throw a rod, or blow out a valve.
Not Good.
I have not worked on one like yours for years, so I don't know off the top of my head what you have.
Hopefully there is an accumulator or chamber of some kind after the evaporator to catch any liquid. But if you see frost heading down the suction line toward the compressor turn it off quick.
 
Mine uses an orifice tube (which I replaced in the rebuild). There is a drier/accumulator after the evaporator so I'm hoping it's doing it's job sufficiently.

Thanks for the head's up on watching the frost, I'll be sure to keep an eye out.
 
I was pretty sure that was how yours worked. Letting liquid get to the compressor is about the only thing that will destroy something really fast.
Low charge, too much oil, air in the system, even an overcharge will cause a system to not work, but will not usually do much damage.
Moisture in the system will turn acidic and eat up stuff, that takes a while.
 
Or it suddenly switched to Celsius.........
 
If its counting down, throw it before it hits 0............
 
Actually my mothers '94 pick up does about the same thing, never had any evap freeze ups until she moved back to Indiana, back when she came out to rescue my broke down Burb from St.Louis area, the ac air vents would eventually slow down in air volume, I realized the evap was freezing up, hit the ac button to shut off the compressor, it started blowing more air within a few minutes. High humid area I am guessing was a major factor in that deal as it never did that while out here in Phoenix,AZ.

I just worked on a couple of others friends ac systems that required a new discharge line on one, ('98 S10 with a 4.3) and a simple Schroeder valve on the other, (96 Chevy 3/4 ton van) both were emptied out before I tore into them, pulled vacuum to ensure mo other leaks and rid of moisture, filled them with Freon and git them down in the same temp range as this Avalanche ac I just took a pic of.

Not sure if its a climate thing or what, but I've never seen the evaps freeze up out here.

These are primarily all factory systems as well, all I did was replace a leaky part and recharge the system to around the factory pressures.
 
I believe I had a slight leak at the high side port valve due to an adapter I used. Measured the low side and it was reading 40-41psi. Removed the high side port adapter and used brake cleaner to remove the UV dye last night. This morning no new dye was anywhere to be found, and I added refrigerant back to 44-45psi. It was blowing 35 degrees on the way to work this morning, with ambient temp around 70 degrees and driving speed of 30mph.

I'll have to take a picture of my "homebrew" copper pipe extension and let you guys poke fun at me :haha:
 
I used soapy water in a spray bottle to find the leaks on the trucks I just repaired. :D

yes, one was the low side valve the other on the s-10 was the high side valve and I didn't see any way of removing that valve, plus I was reading of people having issues with the new valves they somehow replaced would leak shortly after.

I just ordered up a whole new discharge line online for like $35, dealer wanted $140.

I'm gonna find a mechanical thermometer or something today to verify this digital one is right or wrong. I do have to say though, the air coming out feels damn cold to the hand.
 
Last night I'm driving home, and the vent temps seem to continually rise during the 15-20 minute highway drive. When I get home the drier and inlet/outlet lines of the evaporator were frosted over with ice.

Is it possible I have air flow blockage in the evaporator housing? It seems the evap is getting plenty cold, but not bleeding off that cold to the air transferring into the cab.
 
That would do it. But it still should not freeze up.
Don't forget, its designed to work at any fan speed.
I used to have to pull the fan motor off my truck and run a water hose in to wash the dog hair off the fins every couple of months.
My dog went everywhere with me, and he was a shedder.
But, it would just get to the point where it was not moving enough air even on high to cool the truck. It never froze up.

Sounds like that pressure switch is not cycling the compressor right and its freezing up.
Remember, if the evaporator gets below 32 degrees, frost can form. Once it forms, it gets worse and worse as it blocks the air.
Since pressure and temperature are a direct relation, if you control the pressure correctly, the temp will be right.
 
Fordum said:
That would do it. But it still should not freeze up.
Don't forget, its designed to work at any fan speed.
I used to have to pull the fan motor off my truck and run a water hose in to wash the dog hair off the fins every couple of months.
My dog went everywhere with me, and he was a shedder.
But, it would just get to the point where it was not moving enough air even on high to cool the truck. It never froze up.

Sounds like that pressure switch is not cycling the compressor right and its freezing up.
Remember, if the evaporator gets below 32 degrees, frost can form. Once it forms, it gets worse and worse as it blocks the air.
Since pressure and temperature are a direct relation, if you control the pressure correctly, the temp will be right.
Click to expand...

This makes a lot of sense. I'm still waiting on my 134 cycling switch so for now I'm jumping the plug which is causing the compressor to run infinitely.

Fordum, thanks for your input in this thread. You've been a valuable resource and I appreciate it.
 
Just got the 134 pressure cycling switch today, but can't use it yet because I have a somewhat significant leak in the system stemming from my copper pipe extension. I'm going to have to get to the auto parts store this weekend and ask them about where/how to make custom length refrigerant hoses since my stock ones won't reach the necessary length.

Attached pics are as follows:

Copper pipe extension (this did NOT work)
View from driver side of compressor
View from top/passenger side showing new routing of serp belt
passenger side mounts
passenger side shot of compressor (you can see it interfered with my EGR system so I removed it)

1.jpg

2.jpg

3.jpg

4.jpg

5.jpg
 
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well don't give up just yet on the copper pipe extension, was it a pressure fitting or flanged with gasket?
Is it leaking because it's not fitting right or what?
 
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