R134 Conversion Woes - Evaporator Freeze-Up

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ACME A12

ACME A12

It's all ball bearings nowadays...
Joined
Mar 29, 2006
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Location
New Port Richey, Florida
Converted the RV2 on my '74 Duster to R134 when I swapped the /6 for a 340 a few months ago. The air worked great prior to the swap. Had new hoses made to allow for the repositioning of the compressor. Vacuumed the system. Changed o-rings, valve cores, etc to convert. Installed R134 & ester oil at 80% of R12 capacity. Blows cold (not R12 cold, but cold enough) but twice now when I've had the thing out on longer runs (picked the wife up at the airport in it last weekend - about 70 miles roundtrip) the evaporator has frozen up. I've heard of this happening, but never heard what the fix is. Any suggestions? Should I replace the receiver drier to elimate the possibility of trapped R12 particles, and could this be (part of) the cause? I'm sure the Florida humidity is not helping me one iota either... Any help will be appreciated.

Ray
 
My fiance' and I were just having this exact discussion this weekend. I had mentioned that I had converted to R134a and that I should have evacuated the system first as the vent temperature rises when I'm at idle. She asked me if I had replaced the dryer. I said no and she said to be prepared for a freeze-up due to left over R-12. BTW, she's a BMW master mechanic. I can ask her for details tonight, but I'd bet it's your dryer.
 
Sounds like your expansion valve is not working correctly. They usually have a capillary tube that reads the vaporator temp and it adjusts the amount of refrigerant going into the vaporator to keep it from freezing. Basically they are a thermostat.

Chuck
 
OK, just talked to Lori. She had this to say. "Any time the air conditioning system is opened (exposed to the atmosphere), the dryer must be replaced, especially in Florida! The problem isn't leftover R12 but oil and moisture contamination. Also, the dryer should be the very last item to be replaced as it is shipped sealed." She also agrees with Chuck, that the expansion valve can be compounding the problem and should also be replaced, since the system has to be evacuated again anyway.

So, replace your expansion valve, then your dryer keeping in mind to lube all of the o-rings. Evacuate for an hour, according to her, due to the moist Florida enviorment, then see if it will hold vacuum for another half hour. Now, charge with 134a.

She is an acclomplished tecnician who, back in the day even had a hand in installing a hemi in a '87 7-series BMW. I know this sounds like bullshit, but I just got back from Witchita (she had her 25th high school reunion) and visited the shop that this was done in. It's the "European Car Company" and I saw some stuff that blew my mind. Full cage BMW 2002's set up for SCCA racing, a Bentley under restoration, a Porche with a full cage, aftermarket fuel injection and a turbo as big as my head (they had to mount it where the passenger's feet would be so as not to interfere with the front suspension) and a sweet Alfa-Romeo (red, of course) with giant side draft Webers that almost made me cry when they fired it up for us.

Her dad has pictures somwhere of the 7-series with the hemi. When I get 'em, I'll post 'em.
 
Thanks for the input guys. Ramcharger, I was just typing a new post stating that I'd like to get your fiancee's opinion before I start replacing components and then your latest post popped up. I'll follow her advice and replace both components. Anyway, thanks again to both Ramcharger & Chuck. And of course please convey my thanks to the future Mrs. Ramcharger. Much appreciated, and I'll let you know how successful I am.

Ray
 
Ray,

The future Mrs. Ramcharger says "You're welcome! Let us know how it turns out". :yawinkle:
 
Something that nobody mentioned is that in 1974 and up Chrysler used an Evaporator Pressure Valve in the back of he compressor suction inlet to shut off the flow of R12 if the suction pressure dropped too low to prevent freezing the Evap coil up. Previously in 1973 back there was an antifreeze switch wired inline with the clutch to shut off the compresser until the temp came up in the evap. In any R134 retrofit you must install a switch to prevent freeze ups and you must remove the R12 calibrated EPR valve for proper system operation. Chrysler went to this setup in 1974 and up to address the complaint of roughness in the engine when the compressor cycled off and on.
The old RV2 compressors were not known for their smoothness but they were a quite rugged design.
 
Well it has taken me some time to get back to this little story, as it has taken a couple of twists & turns, and my travel schedule only allows me to work on the cars in spurts anyway. So here's the latest:

Shortly after Ramcharger gave me the low down on how to address the evaporator issue the compressor gave up the ghost. I guess it was just its time... So I installed a new (read that as "remanufactured" - this becomes important in a moment...) compressor, expansion valve, and receiver drier following the instructions as outlined by Ramcharger's future Mrs. I even flushed the entire system with some of that $34 a bottle Dura Flush from NAPA prior to the installation of the new parts. I then find out upon initial fire-up that the "new" compressor I've installed is also junk. It was banging & clanging like nobody's business. If I had to guess, I'd make the assumption that they gave me somebody's core rather than a compressor that had actually been refurbished. I quick trip down to the parts store while my blood was still boiling and I was at the wheel of the compressor-hammering beast ensured that they knew I was not to be f***ed with. They ordered a replacement (I insisted on a different brand) on the spot despite the price differential (which THEY ate) and I headed back home and I put it back in the garage where it sat until last weekend when I finally got a chance to get back to it.

Another compressor and sytem flush later all is well. As far as I know. I vacuumed & charged the system on Saturday and it seems to be working well. I need a good road trip to clearly determine that my evaportor freezing woes are behind me. Maybe this Saturday. Meanwhile, I wish that I had read Surfman's post on the EPR valve prior to putting this all back together as I blindly transferred this from one compressor to the other as I went through this entire process... I guess we'll see. I'll keep you guys posted. Thanks again.

Ray
 
I did the 134a “conversion” on a 74. Worked well. Guess because of the EPV valve. If you have further problems a work around is a thermostatic switch to cycle the compressor on and off. (Didn’t notice a mention of this in the thread. May have missed it.)
I won’t bother with 134a anymore for r12 systems. I will use (hope this doesn’t get anyone riled up) one of the “drop in” replacements that I probably shouldn’t name. I like the advantages of it. Less likely to leak being at the top of my list. You can order it off the net.
 
ramcharger said:
OK, just talked to Lori. She had this to say. "Any time the air conditioning system is opened (exposed to the atmosphere), the dryer must be replaced, especially in Florida! The problem isn't leftover R12 but oil and moisture contamination. Also, the dryer should be the very last item to be replaced as it is shipped sealed." She also agrees with Chuck, that the expansion valve can be compounding the problem and should also be replaced, since the system has to be evacuated again anyway.

So, replace your expansion valve, then your dryer keeping in mind to lube all of the o-rings. Evacuate for an hour, according to her, due to the moist Florida enviorment, then see if it will hold vacuum for another half hour. Now, charge with 134a.

She is an acclomplished tecnician who, back in the day even had a hand in installing a hemi in a '87 7-series BMW. I know this sounds like bullshit, but I just got back from Witchita (she had her 25th high school reunion) and visited the shop that this was done in. It's the "European Car Company" and I saw some stuff that blew my mind. Full cage BMW 2002's set up for SCCA racing, a Bentley under restoration, a Porche with a full cage, aftermarket fuel injection and a turbo as big as my head (they had to mount it where the passenger's feet would be so as not to interfere with the front suspension) and a sweet Alfa-Romeo (red, of course) with giant side draft Webers that almost made me cry when they fired it up for us.

Her dad has pictures somwhere of the 7-series with the hemi. When I get 'em, I'll post 'em.
Click to expand...


When you evacuate a system, the proper way to do it: Evacuate to the lowest vaccum you can...usually 29"Vac and let it sit over night to make sure it holds a vacuum. And then run vac pump more, this will evaporate any moisture in the system and remove non-condensibles. Replacing the dryer is one of the ways to go, but a good long vacuum is the best. R134a will get as cold as R-12. Just the old timers like R-12 because it is more controllable.
 
Mopar "A" bodies with the RV compressor did not use the "evaporator pressure regulator valve"...they have a thermostatic switch that cycles the compressor on and off to prevent evaporator freeze up. If your evaporator is freezing up you've got a problem with that switch. Either the capilary tube is not pushed into the fins of the evaporator or the the switch is bad. Easy fix no matter with one.
 
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