R 134a conversion frustrations

[Randy S.]

I converted my 66 roadster w/AC to 134 late in 2003 . Conversion included virtually everything rebuilt or changed including STV valve. Only the evaporator wasn't changed but was blown out to be sure no obstructions. I ran the system all of 2004 obtaining high 40 deg temps. Spring 2005 the ceramic shaft seal on A6 comp failed (rebuilt in 2003). Replaced seal and recharged the system today, a high humidity 93 deg day in Atlanta. AC Shop used 2.5 # R134a ( R12 capacity is 3# 4 oz)

The best we could get today was 60 deg temps at outlet vents with top and windows up and shop fan blowing on condensor. High side pressure was as high as 350psi at 2000 rpm and low side was 35-37 psi. Shop re evacuated and recharged hoping there may have been an air bubble but no significant changes.

What are we missing??

Randy

[lyndon sharpton]

Re: R 134a conversion frustrations

R12

[Jack H.]

Re: R 134a conversion frustrations

Your A/C shop ought to be able to troubleshoot & fix this since they DID have the system running properly at one time! A couple of comments:

(1) It's pretty rare for a ceramic seal to bite the bullet that fast! One thing that CAN do this is IF the mechanic who installed the ceramic seal failed to adhere to proper handing methods during the R&R process...

CLEANLINESS is the watch word and you should NEVER physically handle the ceramic bearing/seal during the change out process. That's why some suppliers of seal kits pack a 'redundant' component (a metal 'washer') with the bearing and seal that facilitates moving the seal from the kit and getting it into the compressor without having to physically touch it...

(2) Hi/low pressures are important, but they're only part of the overall equation. You need to be MOVING refigerant through the evaporator as well as moving AIR through the evaporator's cooling fins to get bottom line results.

(3) It's NOT uncommon for roadway debris (leaves, bugs, pin needles, Etc.) to accumulate in the Harrison heater box and 'plug' the passageway(s) of the evaporator's cooling fins. About the only way you can determine whether this is a factor is to either de-mount the air box from the firewall and physically inspect it OR use an optical aid (like a borescope) to look inside by removing the 'weep water' bladder on the bottom of the air box and viewing what's what....

Good ole boy, 'rate buster' mechanics from the era used to have cleaverly improvised flexible extention hoses for their shop vac's to be able to suck the air box clean through the weep water hole and save the labor associated with physically pulling the air box!

[Jim T.]

Re: R 134a conversion frustrations

Randy I wish I knew a lot about air conditioning systems, only know a little bit. Based on what you have told me I would have the system evacuated of 134 and if what I know is correct on your 66 you have a expansion valve like what is on my 70. The line going to the expansion valve from the condensor has a very small metal filter. If this filter has done its job, it could be restricting the flow enough to not permit proper cooling. You did not mention changing the dryer. If you evacuate the system to check the expansion valve filter I recommend the replacement of the dryer. What had clogged my expansion valves filter back in 1988 was desiccant that was supposed to be contained in the dryer. To remove this small filter screen I found that carefully inserting an easy out and turning it did the trick for me. I did buy a new filter and o-rings at the parts store. If you find the screen clogged I recommend removing the dryer and flushing from the output line of the dryer through the condensor to the end of the removed line from the expansion valve. You can buy flush at parts stores. If this is your problem, it is really an easy fix.

[Randy S.]

Re: R 134a conversion frustrations

Thanks Jack

Re the ceramic seal; that was installed by Classic Auto Air that rebuilt the compressor etc first time around. I assume they know how to handle the seal but maybe you are right...Their explaination for the failure was that I did not use the system for a few months in the winter of 2004. I don't buy that but they are the experts. They also reinstalled the second ceramic seal because local shop was not able to locate the specialized snap ring tool to remove.

Re shop's trouble shooting our next step is to adjust the STV valve's low side pressure . Classic says they can rebuild STV then but they can't preset them and for optimal efficiency with R134a they say the low side pressure should be around 20 psi. Since we were getting high forty's temps at vent before I am not sure we are going to get significant improvements.

Good comments re evap debris. In the event there is debris in there can it be removed by flushing water thru the drain hole? I suppose it is not recommended to stick coat hangers up there as it may possible damage the fins.

Thanks again for the input

Randy

[Randy S.]

Re: R 134a conversion frustrations

Jim,

I had the expamsion valve and drier rebuilt in the summer of 2003 when I went thru the system. If I have the system evacuated, I check that filter.

Randy

[Jack H.]

Re: R 134a conversion frustrations

"Good comments re evap debris. In the event there is debris in there can it be removed by flushing water thru the drain hole? I suppose it is not recommended to stick coat hangers up there as it may possible damage the fins."

The weep hole is centered in the bottom of the air box while the evap core sits in a vertical plane with respect to the weep hole. You'd have to flush water up onto the evaporator's cooling fins and I see two problems there:

(1) You'd be potentially pushing 'crud' INTO the cooling fin passages vs. sucking it OUT.

(2) I'd expect a healthy portion of the wash water to go through the evaporator making it dribble out the back side and into the passenger compartment (kindy messy...).

[Randy Krohn]

Re: R 134a conversion frustrations

Seems to me like I've read somewhere that you can remove the fan resistor from the airbox and inject water into the box there, and let it drain from the weep hole. I've not tried this myself.