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78 GHOST · 05-13-2003, 05:31 PM

Hi:

I have a 78 T/A converted 1 1/2 years ago to R134A refrigerant. Since the conversion, I've never been really happy with the cooling of the system.

Today I put gauges to it and here is what I found: (Readings with a "warm" engine, A/C on, at 1500RPMs)

Low Side = 38 PSI no fluctuations at all
High Side = 330-340 PSI steady
A/C Clutch Cycling Rate = Continuously on

According to the instructions it says that high readings on both sides indicates moisture in the system. When I redid the system, EVERYTHING was replaced including the receiver-dryer.

Any thoughts? Also, when you add refrigerant, do you do the gas method or the liquid method? Is there a good evacuation device for the home mechanic?

Thanks, Matt

P.S. The good thing is the damn thing didn't get hot after an hour of driveway abuse in the Houston heat and humidity.

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

78 GHOST · 05-13-2003, 05:31 PM

Hi:

I have a 78 T/A converted 1 1/2 years ago to R134A refrigerant. Since the conversion, I've never been really happy with the cooling of the system.

Today I put gauges to it and here is what I found: (Readings with a "warm" engine, A/C on, at 1500RPMs)

Low Side = 38 PSI no fluctuations at all
High Side = 330-340 PSI steady
A/C Clutch Cycling Rate = Continuously on

According to the instructions it says that high readings on both sides indicates moisture in the system. When I redid the system, EVERYTHING was replaced including the receiver-dryer.

Any thoughts? Also, when you add refrigerant, do you do the gas method or the liquid method? Is there a good evacuation device for the home mechanic?

Thanks, Matt

P.S. The good thing is the damn thing didn't get hot after an hour of driveway abuse in the Houston heat and humidity.

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

meanolegoat · 05-13-2003, 05:57 PM

First of all i've never heard of moisture just appearing in a system. I kind of doubt that to be the case. What kind of temp/humidity did you have when you took the readings?? It is a little stout on the high side. How did you convert the system?? Did you make any changes as far as fan clutch, cycling switches, etc..?? Also what charge amount did you put in, there is a conversion table from r12 to r134a. I dont recall the exact formula (i can look it up though). But the 134a conversion takes less than the 12 charge amount. Also 134a is not as forgiving as the 12 in regards to the charge amount. Sounds to me to be a tic overcharged (maybe a 1/2lb.) or the fan clutch is giving up. As for a cheapo evac system, they used to make one that you could hook to an air line on your compressor to pull it down. They worked ok but took longer than the traditional electric vac pumps.
"mean"

NOZZLENUT05 · 05-13-2003, 06:25 PM

how is your orifice tube?

meanolegoat · 05-13-2003, 06:32 PM

Good ?, if its a ccot system. I'm really not sure. I would have thought that it used a poa.....
If it is a ccot, I would defintaly check the orofice...
"mean"

78 GHOST · 05-13-2003, 06:40 PM

Mean:

When I converted, we used all the original sized Evap. Cond. Comp. and Receiver Dryer. All original components were used. I'm aware of the conversion ratio and we used that when loading the system.

I changed the little plastic screen deal in the orifice tube way back when.

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

NOZZLENUT05 · 05-13-2003, 09:07 PM

What system are you using? Is it original to the car? you just went from r12 to r134a? I have seen many orifice tubes get clogged almost immediately on cadillacs. I have put in 2-3 on some cars after replacing a tore up compressor. You might want to check it just for P.O.M. Do you know how much 134 is in the system?
Nozzle

Lloyd-TX · 05-13-2003, 09:37 PM

78 Ghost:

That old R12 designed condenser just isn't up to the task of operating with R134A refrigerant. R134A condensers are MUCH more efficient designs. "Bump" me at work during the day, either by e-mail or phone, and I'll attempt to find out if anyone markets a R134A compatible high efficiency condenser for a 2nd gen F-body. Since that's doubtful, my suggestion would be to revert the system back to R12.

Alternatively, you could TRY an electric pusher fan in front of the condenser and/or a different fan clutch, or (horrors) a HD flex fan to improve air flow across the condenser. You should also seal ALL cracks between the fan shroud, radiator and condenser with foam tape to further improve air flow.

Hope this helps,
Lloyd

'72 Formula 400 - soon to be a 455HO, TH400, A/C, etc.; Lucerne Blue with Medium Blue Interior
Restoring a '72 GTO 455HO, TH400, A/C, etc.; Sundance Orange with Parchment buckets

LouisianaGuy · 05-13-2003, 09:38 PM

Also just a little too much oil in the system can cause it to blow up to 14-15 degrees warmer than it really should.
Swapped compressors on my wifes 96 ETC and had a tad too much oil built up in the syatem and the temp was blowing a steady 52 degrees, i pulled the system down and flushed just the Condensor, and got just a little oil out of it, maby 1/4 oz maby, then recharged the system and it immediatley dropped to 38 degrees when crusing, so may wana look into a slight oil over charge. This would not be the first time i have seen that happen.
Also you may wana look into some Freeze12 it works Great.
Mike

stu · 05-14-2003, 06:37 AM

It looks overcharged to me, shouldn't the low side be in the high 20s - low 30s and the high side around 220-240? And the fact that the clutch isn't cycling and poor cooling would lean me in that direction. I went through a bunch of hassle fixing my R-12 system in my 79 Formula, it was seriously overcharged by the shop that put the R-12 back in after I changed the O-rings, compressor, and accumulator. It's still not quite right, I suspect it's not getting enough flow thru the rad due to the solid nose. I'm going to a late model dual fan this summer to try to mitigate my problem.

LouisianaGuy · 05-14-2003, 08:53 AM

Yes sounds a little overcharged, but put a fan in frount of the condensor nad see if the high side goes down and the temp drops, if so might be a good indication you need more airflow as well.
Mike

JC455 · 05-14-2003, 12:00 PM

Great suggestions, one and all.
I thought I read something regarding the changing of the high limit pressure switch when you convert to 134a.
It seems like it was in a Vintage Air article, or possibly on their website.
Re: Freeze12. Is this stuff any good? Obviously the salesmen think it's the cat's meow, but I would like to here some real world evals.

John

78 GHOST · 05-14-2003, 03:37 PM

Thanks everybody for all the excellent comments. Now that I know the system is "tight" and not leaking after having been through it, would it be possible to switch back to R-12?

Seems like I've heard you can switch to R134, but not back. Is this true?

I'd rather spend the bucks on R-12 than changing to a larger Condenser.

Thanks guys, -Matt

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

TinInjun · 05-14-2003, 04:04 PM

Matt:
What was the OAT, humidity, and duct discharge temp. We can then go from there.

Don't think you want to spend the money to change back to R-12. It involves the same thing you did to retrofit to R-134a.

"Suppose you were an idiot... And suppose you were a member of Congress... seems I repeated myself." --Mark Twain

Bartman · 05-14-2003, 04:09 PM

Actually the condenser will probably be smaller than what you have now. The ones designed for 134a have smaller tubes and a higher fin count plus they usually are a multipath design.
I converted mine a while ago and I've never been happy with it. Mine just cycles to much going down the road. I've tried various Orifice tubes (Fords use different size orifices in their's) and even a variable OT. The only thing that helped somewhat is I converted mine to a cycling switch and adjusted it down to cycle off at 15psi.
As far as your car goes, did you use ester oil. Do you have the proper amount in it. It sounds like you have your system overcharged. I'd shoot for no more than 275psi on the high side. Try running water over the condensor. If your a/c works a lot better then you need more airflow or just a more efficient condensor.
Bartman

Ponies run but Birds fly

78 GHOST · 05-14-2003, 04:28 PM

George and Bart:

I forgot to mention the WX at the time of my measurements. It was in the low nineties and very high humidity. I couldn't measure the discharge temps, but the temps felt to be in the 50-55 degree range, not hot but certainly not cold.

I didn't think to try the old water hose over the condenser trick, I'll try that next time.

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

LouisianaGuy · 05-14-2003, 04:45 PM

put a box fan in frount of it also and see what happens.
Mike

TinInjun · 05-14-2003, 05:02 PM

50 to 55 duct temp is great for those ambient conditions. High side pressure is high but I have seen this before with 134 conversions and low airflow through the condensor.
Check the duct temps with a thermometer and get back with me. My charts say it should average 68 degree duct temps with those outside conditions

"Suppose you were an idiot... And suppose you were a member of Congress... seems I repeated myself." --Mark Twain

78 GHOST · 05-14-2003, 05:31 PM

Thanks George, I'll do that.

____________________________________
"Gee, what's that goat doing way up here in a cloud?" -Gary Larson

TO THE MILITARY FORCES CURRENTLY ACTIVE, AND THOSE THAT HAVE SERVED; THANK YOU FOR YOUR SACRIFICE FOR FREEDOM. PLEASE COME HOME SAFE.

meanolegoat · 05-14-2003, 06:25 PM

From the sound of it...its a ccot system, definatly check the orofice tube. To compensate for the condensor, find a fan with the most blades you can and install with a heavy duty cooling clutch. I put one on my 75 t/a from a g body van and it worked great. I still suspect overcharge. If it has an adjustable cycling switch, you can tinker with that also.....
"mean"

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