AC Receiver Drier Bad??

hifeverz · 07-28-2007, 02:34 PM

AC Receiver Drier BAD???!??

I have a 1979 911SC with Air Conditioning system that I worked on over a year ago and everything seemed to operate well. The receiver drier site glass indicated refrigerant flow by the movement of the floating ball.

Before conversion the system was evacuated of the old R12 refrigerant. I then changed out the condensor assembly in the smuggler's box, installed a new compressor, a new receiver drier, again evacuated the system for 45 minutes and converted to 134a refrigerant. This summer, it was still blowing cool but not as cold as I would like. I proceeded to charge the system with more 134a. I noticed, while engine running and AC and compressor running, before charging, the float ball in the the site glass (on receiver drier) was at the top, but NO liquid seemed to be flowing. I attached hoses and opened suction (low pressure) side valve and installed temp gauge at interior vent. While engine running and AC engaged to charge, the float ball remained on the top side of the site glass and still no liquid flow was evident. However, after a few minutes of charging 134a, and the running, the temperature eventually dropped to 49.4 degrees F at the vent. This I felt was good enough. I went to see the float ball in the sight glass which was still in the uppermost level and still NO liquid seemed to be flowing. I shut the engine off, waited a few minutes to see and it is as if the ball is stuck in that position and with no evidence of liquid or moisture ever being present.
What is amiss here? Clogging due to contaminants and thus turned to a defective and Bad receiver drier ?? or what?? Why is system cold though site glass shows NO flow?? The hoses to and fro the receiver drier were neither hot nor cold which leads me to believe NO FLOW through it.
Thanks is advance to any hints or help rendered.

HZ

equality72521 · 07-28-2007, 02:44 PM

If you have complete liquid seal the ball will be at the top and appear to have no liquid. The liquid is absolutely clear. When you see bubbles you are low on charge. You have non-condensables causing bubbles to appear. The temperature of the line sets to and from the receiver will be near ambient since the hot gas from the compressor has already left the condenser and is on its way to the receiver and then leaves on it's way to the TXV. The receiver is just that, a reservoir for liquid refrigerant.

scottb · 07-28-2007, 03:25 PM

I have a vague recollection that the site glass is no longer used after a conversion to 134. You might do a search to confirm this.

hifeverz · 07-31-2007, 01:46 PM

AC Problem

Thanks for the hints. I however noticed a problem, the next day after the charge of added 134a. The day I charged the system, the vent temp. read 49 degrees F. The next day the system was NOT cold at ALL, in fact it read about 72 degrees F. Could Over-charging cause this?? I did NOT use my gauges when I added more 134a. It was just a random boost (liquid)charge from a large tank of refrigerant. The compressor is engaging and the receiver drier sight glass appears still full.

What is going on here? Help!!
Hz

scottb · 07-31-2007, 01:54 PM

If it was at 49 one day, and 72 the next (assuming ambient air temp and humidity on the next day were similar to the first day), chances are you have a leak somewhere.

Hugh R · 07-31-2007, 03:41 PM

A R-12 R/D is not suitable for R-134a, it has a different dessicant, which can degrade and plug the expansion valve at the evaporator. Also, you need to put R-134a oil in the system. The R-12oil won't get picked up by the refrigerant to lubricate the compressor. If you put refrigerant in as a liquid, you run a big chance of hydrolocking the compressor and destroying it. Make sure your wearing goggles, refrigerant can blind you.

hifeverz · 07-31-2007, 04:47 PM

AC Problem

Thanks Hugh R for the tips. Upon initial charging with 134a, I did use the correct compatible oil. However, I am NOT aware that the R/D in not compatible likewise for either R12 or 134a. I've read other threads re. conversion and do not remember an issue as such. I cannot remember parts houses differentiating their R/D segregation for specific refrigerants. Can someone point me to a source that specifically states so?? I would like to correct my installation if need be. I have a 300SL Mercedes and I did the same conversion, using an R12 system R/D in the 134a refrigerant charge application. It has been 3 years or operation (daily driver) with the 134a and have NOT had problems. Was I lucky or ?? As far as the hydrolocking . . . yes I have had 1st hand experience and well aware. Liquid charge is always quicker than gas charge. I was just too lazy to drag the guages out and do a precise job.
I do believe the expansion valve is clogged as I also had this experience on another vehicle, that would produce NO cool though compressor was engaged and refrigerant filled. Upon replacing the valve, the system worked well.
Is there a way to unclog the expansion valve for reuse or is it terminal??

Thanks,
Hz

Jim Sims · 07-31-2007, 08:36 PM

Unless you somehow obtained a new old stock (NOS) R-12 R/D the new R/D is probably okay as most units sold in recent years are dual use for both R-12 and R-134a. Overcharging can cause your problem (insufficient cooling and no vapor bubbles in the sight glass.) One can't really properly charge a 134a system without using gages. Before you do anything else, I suggest you install the gages and check for overcharging. If the expansion valve is clogged you may be able to restore it; check for debris on the inlet screen. However the expansion valves are not very expensive so if I detected one that was clogged I would just replace it. Cheers, Jim Sims

T77911S · 08-01-2007, 09:48 AM

try polarbear.com or polarbearinc.com
they have great prices and the guy will help you T/S on the phone.

hifeverz · 08-02-2007, 01:18 PM

Receiver Dryer

Jim:
I DID get and install a NOS factory Porsche R/D. Does that mean I need to replace (again)?? . . . along with expan.valve?? I'll check system pressures with gauges before I R&R the system . . . maybe I'll get away with it! Thanks for the expert advice.

T77911S:
I was looking at the site you advised on polarbearinc.com and it is a good diagnostic lead for all DIY'ers. Nice straight forward info on auto AC systems. I'll check pricing when I'm ready to redo my AC. Thanks loads!

Hz

T77911S · 08-07-2007, 05:14 PM

call him. he is VERY nice and helpfull. he will T/S over the phone. the lady there is very knowledgable too, cant ever remember her name.

ive opened a system up after replacing the drier and reused it, plug the drier so it is not open to air while it is out. i vacuum down for several hours, even over night...pump off with gages closed.