A/C Recharge for converted system

[The Critic]

My dad has a 92 Toyota Previa that was hack converted to R134A about 5 years ago. If I recall correctly, I fixed the leaks, add some ester oil, replaced the drier and had it professionally evac-ed/recharged to around 80% of the original R12 capacity with R134A.

The system worked adequately for about 3-4 years but then started to slowly deteriorate in effectiveness, likely because it was slowly losing its refrigerant charge. Even when the system was working, the compressor would disengage/engage every min or so. At the time I was not sure what the problem was, but did not pay much attention since the system still worked fine.

Anyway, fast forward to this month, the system was no longer working great so I added a can of R134a. Bad, I know. It worked fine again with none of that on/off action from the compressor, but I got a bit greedy and decided to add another 1/4 can for good measure.

Somehow 1/4 turned into 2/3 a bit more quickly than I realized. Now the compressor shuts on/off every 5 sec or so and the system barely works.

So, here are my questions:

1) Is the compressor's constant on/off action caused by a refrigerant overcharge? I am assuming yes.

2) What is the correct R134a charge for a R12 system that holds a maximum of 2.86 lbs? The label under the hood does give a min to max range. Someone told me that the R134A charge should be about 80% of the original R12 charge.

3) If the compressor still cycles on/off excessively after the system is charged to the correct amount of R134A, where should I begin the diagnostic process?

Thanks!

 

[Jarlaxle]

Should take about 2.2-2.3lbs of 134a.

 

[JHZR2]

Do you have real gauges? Let us know the pressures with front and rear air handlers working.

 

[Colt45ws]

Yeah, you need to get a gauge set on there and find out what it is doing.

 

[The Critic]

I do have a set of gauges from HF but the knobs are cracked. I think I will take it to Sears tomorrow for their $90 recharge special and have them diag, evac and recharge as needed.

 

[JHZR2]

I think that is a great idea. Have them add dye so that you can trace leaks in the future.

And honestly, R12 just works so much better, that if the lubricants you mixed in there allow, Id see if they will put R12 back in...

 

[TFB1]

Originally Posted By: The Critic


1) Is the compressor's constant on/off action caused by a refrigerant overcharge? I am assuming yes.

3) If the compressor still cycles on/off excessively after the system is charged to the correct amount of R134A, where should I begin the diagnostic process?

Thanks!


Sears may not want to service a converted system...


I'd try to at least monitor low side pressure... If it rapidly falls to under 25-30 psi when cycling, the system is low on charge... If pressure is constantly above 40psi and it cycles it's possibly over charged or has a restriction...

Of course the above assumes the low pressure switch is in good condition, I've seen failures... BTW when converting to R134, the low pressure sw should be changed to a one for the new refrigerant, as pressures are different... Could have been the root of the constant cycling issue...

 

[The Critic]

At Sears right now. The machine recovered 3.19lbs of 134A. Per the Toyota TSB, the correct charge amount should have been 2.53lbs or 1150g. The max R12 charge amount would have also only been 2.87lbs.

So yeah, oops.

 

[JHZR2]

Would they put R12 back in?

 

[Shannow]

Are those volumes typical ?

most of the stuff that I've read on Oz systems is around 1 lb of 134.

 

[JHZR2]

The previa not only has the front vents, but also an air handler for the rear seats... Like a whole fan coil assembly back there. SO thats a lot more charge needed.

 

[mechanicx]

It wasn't too uncommon for cars here to have 2-3lbs R12 capacity back in the early 90's even with out rear air. My '03 Impala holds 2lbs of R134a although 1.75lbs or less is more typical for that time period. They just keep dropping it lower.

 

[bdcardinal]

Originally Posted By: JHZR2
Would they put R12 back in?


I was working there when they rolled out the A/C service to our store. WE were not allowed to touch R-12 systems, besides we didn't have the tools to deal with R-12. Literally all they were allowing us to do was evacuate, vacuum and recharge. They were not authorizing the stores to perform repairs.

Now even though a few of us had the EPA and ASE certs and we had the equipment, we were not allowed to even do the service because none of us were "Sears Certified".

 

[Rock_Hudstone]

Originally Posted By: The Critic

Anyway, fast forward to this month, the system was no longer working great so I added a can of R134a. Bad, I know. It worked fine again with none of that on/off action from the compressor, but I got a bit greedy and decided to add another 1/4 can for good measure.

Somehow 1/4 turned into 2/3 a bit more quickly than I realized. Now the compressor shuts on/off every 5 sec or so and the system barely works.

Okay, so you probably overcharged it a tad, no big deal. I don't know why people panic when they add a little too much refrigerant.

Should have just bleed some off the low side shrader valve until the compressor to stop cycling.

 

[Rock_Hudstone]

Originally Posted By: JHZR2
And honestly, R12 just works so much better, that if the lubricants you mixed in there allow, Id see if they will put R12 back in...

He has a very old leaky system that been previously converted to 134a, definetly not a good candidate for the hassle and expense of changing back to R12.

 

[The Critic]

So, I was able to catch the tech just as he was ready to inject PAG oil into the system. The system was converted and Ester is used. As a result, they had to order Ester oil from the auto parts store.

In the end, 2oz of Ester oil was added and 2.5lb of refrigerant was pumped back in. A/C compressor no longer cycles, and the system was working reasonably well again for a 90F day.

All it cost me was $90, oh, and plus the $25 in refrigerant I previously wasted.

 

[MONKEYMAN]

Sometimes that is the price you pay for knowledge. I bet you are not so greedy the next time....

I learn more from my mistakes and the mistakes of others. So, thanks for saving me $25.00.

 

[The Critic]

Originally Posted By: MONKEYMAN
Sometimes that is the price you pay for knowledge. I bet you are not so greedy the next time....

I learn more from my mistakes and the mistakes of others. So, thanks for saving me $25.00.

Indeed.

So, the tech was able to evacuate 51 ounces. The correct charge was 40 ounces, per the revised TSB for 134A converted systems. The original max R12 charge was 46 ounces.

I added about 1.5 cans, or 18 ounces. This means that before I touched it, there was probably 33 ounces.

If I had stopped after one can (12 ounces), I may have had 45 ounces...and been OK. Oh well.

 

[JHZR2]

Originally Posted By: Rock_Hudstone
Originally Posted By: JHZR2
And honestly, R12 just works so much better, that if the lubricants you mixed in there allow, Id see if they will put R12 back in...

He has a very old leaky system that been previously converted to 134a, definetly not a good candidate for the hassle and expense of changing back to R12.


I dunno. I know a number of folks who have maintained thir MB R12 systems and they work well. My R12 MBs dont leak and are all original exccept for the R4 compressor on one (go figure, theyre weak...).

Utilizing the correct leak-searching processes (e.g. Nitrogen with R22 for leak checking, then evacuation, repair and refill with the correct refrigerant) is neither the end of the world nor rocket science. If something like an evaporator is leaking, one must make an executive decision, but personally, Id want it fixed as I dont like breathing R12 or 134a.

If the van is worth keeping (our 94 has 230k and is like new inside and out, and shows no signs of quitting - Critic's has half the miles and should have a ton of life left), why not do the right job, using the refrigerant that was designed for the system, and get a properly functional system?

I understand there are more considerations to be made, but if keeping the van, why not do it right? R12 has come down in price too...

Granted I have a 91 BMW converted and running 134a that blows cold on 105F tarmac. I topped up a slightly low charge for the first time this summer (retrofitted when the compressor bearing got growly in 2004). They can work well, but in hindsight, the right refrigerant still is preferable if the system is tight (or repaired) and the car is worth fixing.

If doing a 134 retrofit, a parallel flow condenser is really mandatory if the car didnt come with one as fit with R12 for optimum performance.

 

[Shannow]

Originally Posted By: JHZR2
The previa not only has the front vents, but also an air handler for the rear seats... Like a whole fan coil assembly back there. SO thats a lot more charge needed.


Makes sense then.