zekgb

I have a freshly flushed and evacuated system with a rebuilt compressor and hoses along with new expansion valve, drier and o-rings. The local shop that does R12 recharges (and is turning out to be only semi-competent at best) attempted to charge the system today and was only able to get about 1.25 lbs into the system even though he tried charging via the low side with the compressor running. Ambient temp today was about 80 degrees and he reported seeing initial low side pressure of 60 or so and the vent temp was 42. Within 5 minutes the vent temp rose to 65 and low side pressure was at 75. For some reason he didn't take a high side reading (apparently didn't even hook up the high side gauge)and then called me with his diagnosis of a restricted/blocked condenser. Dismissing the obvious incompetence of not even hooking up the high side gauge, does this sound like a reasonable explanation?

The Forgotten On

A condenser like ours needs a HUGE piece of debris to block it. It is more likely the front condenser fan not turning on and getting heat out of the refrigerant.

He really needs to take a high side pressure reading to make certain what is really going on or you are guessing at best.

I had a similar issue in my 81 where the doors inside of the HVAC box weren't adjusted correctly.

They were keeping the system from recirculating air and getting the refrigerant circuit heat soaked by cooling hot air sucked in through the cowl instead of already cool air from the cabin.

griffiths

Ignoring the high side pressure for the moment....

You said you flushed the system, let's assume you flushed the condenser thoroughly and you also were able to dry it out (no flushing solution left in the core),

A low side pressure of 60, assuming that's an operating pressure and not a static pressure, sounds a bit odd with a 40F vent temp.


Since the low side is running higher than normal with an undercharge you might want to consider whether the reed valves in the compressor are sealing and the pistons and bores are tight: this you can determine by getting both the low and high side readings at idle and noting the exact amount of refrigerant and the ambient (outdoor) temperature at the time.

zekgb

Just as a follow up I contacted the R12 shop and said I wanted to bring it back in to get a reading on the high side, he hemmed and hawed and finally said that he was having an issue with his Snap-On Recovery/Recharge unit and it would be next week until it was serviced. Needless to say I decided it wasn't going back there and switched my plan to recharging with R134. Replaced the dryer and fixed a badly leaking schrader valve on the compressor that held vacuum perfectly and the system was showing 35/150 at 70 degrees ambient at idle. Today on the freeway it was blowing 38 degrees at the vent with 80 degree ambient. It wanted to go lower but I assume the freeze switch was kicking in to keep temps relatively constant at 38 degrees. No sign of leaking and static pressure today is pretty much identical to yesterday but also did several passes with the HF leak detector (which easily found my schrader valve leak) and it didn't find anything.

Crossing my fingers that I'm done with HVAC for a while.

griffiths

Awesome !


All 3 of my past sharks ran perfectly fine with R134a

white93nsx

Kevin, do you have the procedure for the R134a conversion and did you buy a Griffiths kit? Also, how do you flush the A/C system?
I just put gauges on my A/C system and ran the A/C and it had no pressure on the high side and only 30psi on the low. The window looked like there was nothing in the system at all. I've had no A/C for about two years now so time to remedy that.

Thanks,
Mike

zekgb

I wasn't at all confident with my capabilities in this area so I thought I would have a shop tackle the hard stuff initially. I had my suction and pressure hoses rebuilt and repaired the line from the dryer to the expansion valve using Greg's kit. I also changed out the compressor and bought new dryer and expansion valve. I then loosely assembled everything with fresh o-rings and took it to a shop to have the evaporator, condensor and hard lines flushed. The shop ended up replacing a couple of o-rings on lines that needed to be taken apart to do the flush. They then did a vacuum test (but not a pressure test which was a mistake) and I then took it to the other shop that does R12 recharges but doesn't have a lot of shop capacity for the work above (and who turned out to not be very competent.)

For the R134 charge I rented gauges and vacuum pump from autozone and once I found the schrader valve leak it was pretty straightforward. Still blowing 38* today with 90+ ambient. If I had to do it over again I would have just rented the flush kit as well and tackled the whole thing myself and probably bought all the other pieces besides Greg's kit from them Griffiths.

Griffiths should weigh in but 30 low and zero high is weird and might indicate a compressor problem. Having done this once I would consider myself at least partially helpful if you decide you want to tackle it yourself and want some help.

Edited to add: One thing to check on is whether your gauge plug is atually depressing the high side schrader valve pin.