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Deanj
05-19-2017, 02:23 PM
Yesterday we reached 90 degrees and there wasn't any cold air blowing from my 1960 factory A/C. This unit was converted to R134a some time ago before I bought the car. The compressor comes on. I thought I'd get those single low pressure side refrigerant kits and add 134 if needed.

Now that it is 55 degrees, the low side will go up to 75 PSI before running the engine. After starting, the low pressure reading might even go to 85.

I've read this could be a faulty bypass control valve or a "weak" compressor, whatever that means.

It sounds like a job for Superman.

Dean

Wyldie
05-19-2017, 06:19 PM
Hi

Your low side pressure should be down around 25 psi, 75 psi is way way way to high. Without knowing your high side reading at the time it's hard to diagnose. But 3 possible scenarios pop to mind.
1. Your system is over gassed. You should never need to add 134a to the system. More gas does not mean better a/c
2. There is not enough airflow across the condenser and you're​ not removing benoufh heat from the high side which in turn makes your low side higher
3. Your compressor is not pumping meaning your low side doesn't come down and your high side won't got up

Best I can do without knowing high side readings. Is the clutch definitely engaged and the centre on compressor pulley is spinning (magnetic clutch). That is seriously high low side pressure if so

jopizz
05-19-2017, 09:36 PM
You should be around 25-30 on the low side and 200-250 on the high side depending on the temperature. 75 without the compressor on is just the static pressure. That's normal. 85 on the low side with the compressor running is way too high. I would not add any more refrigerant with the low side pressure that high.

John

Deanj
05-20-2017, 10:32 AM
This compressor was replaced October 2015. There's nothing obstructing the condenser, and the clutch comes on. I'm having the experts take care of this. Even if it were a faulty bypass control valve I couldn't evacuate the system to replace the valve.

I ordered a new $22,500 1992 Thunderbird Sport back in the day. Under warranty the A/C, Heater Blend Door, Brakes Power Assist, Rotors, and Speedometer failed. Once that same mechanical odometer turned from 5,999.9 miles over to 5,000. After I sold it the transmission failed and the rockers rusted out.

I'm still having better luck with the 1960.

Dean

simplyconnected
05-20-2017, 11:05 AM
...Your low side pressure should be down around 25 psi, 75 psi is way way way to high. Without knowing your high side reading at the time it's hard to diagnose. But 3 possible scenarios pop to mind.
1. Your system is over gassed. You should never need to add 134a to the system. More gas does not mean better a/c
2. There is not enough airflow across the condenser and you're​ not removing benoufh heat from the high side which in turn makes your low side higher
3. Your compressor is not pumping meaning your low side doesn't come down and your high side won't got up...

You should be around 25-30 on the low side and 200-250 on the high side depending on the temperature. 75 without the compressor on is just the static pressure. That's normal. 85 on the low side with the compressor running is way too high. I would not add any more refrigerant with the low side pressure that high.

John

This compressor was replaced October 2015. There's nothing obstructing the condenser, and the clutch comes on. I'm having the experts take care of this. Even if it were a faulty bypass control valve I couldn't evacuate the system to replace the valve... Dean, do you hear what these guys are saying? If your system was drawn down for a new compressor over a year ago and it still has too much low side pressure, I think that's proof that it could have too much refrigerant is in your system (if you have proper air flow on both ends).

Evaporation makes cold. <--take this to the bank. If you don't have a big pressure drop at the orifice, there can be no evaporation (and no cold). Also, if the condenser cannot shed heat, your pressure will keep climbing until the relief valve spews refrigerant all over in a huge white cloud. Do you have an electric fan? Have you tried cooling the condenser with a garden hose? Try it and see if that makes 'cold' in your car. - Dave

Deanj
05-21-2017, 12:06 PM
Dave, if there's too much R134 in the system, why did it work from 11/2015 to 11/2016? What made the charge too high if no refrigerant was added?

I ran it in April 2017 and suspected it wasn't blowing cold air before our temporary heat wave last week.

Should I purge some refrigerant? I can't recover any.

Dean

jopizz
05-21-2017, 12:23 PM
A high reading on the low side doesn't necessarily mean you have too much coolant. You could have a blockage or some other issue. Without having a gauge reading on the high side we are just guessing. Either way I wouldn't add any more refrigerant.

John

DKheld
05-21-2017, 03:13 PM
I just converted my old 1987 truck from R-12 to R-134 couple of weeks ago.

The OEM worked great for 20 years with the R-12. Developed a leak and all the Freon leaked out over the winter of '07 ish. Replaced all the seals and drier and refilled with "Freeze 12" which was a cheap R-12 replacement at the time. Supposedly compatible with R-12 systems and mineral oil. That worked fine for about 2 years then started leaking again. Replaced seals again with the HNBR "green" seals and used a different refrigerant this time because the Freeze 12 had disappeared and if you could find it the cost was as much as R-12.

Apparently the new stuff (can't remember what it was) was not compatible with the old seals and eventually eroded the compressor front seal that I didn't replace - lasted about one summer. Also would occasionally carry all the mineral oil out of the compressor and make the compressor lock up.

This year I bought a reman compressor, new seals, new drier, flushed the system and went back with R-134 (which I hear is also on it's way out - :rolleyes:) and PAG 100 oil. Also bought a vacuum pump and gauges to do it right. (roughly $400 for everything)

Outside temp was in the mid 80's and I had 42 deg air out of the vents sitting at an idle when I completed the conversion. Freezing cold going down the road. Gauges read about 50 on the low side and 200 on the high which fell in the correct range for R-134 on my system given the outside temp.

So far so good although supposedly the R-134 molecules are smaller than R-12 and after a couple of years can leach out of the R-12 style hoses that are not lined with Teflon and you have to add Freon occasionally - we'll see.

Bottom line - probably if I had taken it to a shop on the first trouble and had it converted right I wouldn't be working on it for the 3rd time - :o.

The shop sounds like a good plan to me - let us know what the problem turns out to be.

Eric

Deanj
05-21-2017, 04:02 PM
I take it in for service Thursday ( Better not rain ). It behaves strangely in that the Low Pressure static reading slowly reaches 75-and stays there with no effect whatsoever with the engine is running. There is refrigerant or least something making pressure. Like you say, let's see what the expert says since I can't see investing in equipment.

Deanj
05-25-2017, 03:58 PM
It's raining and I don't have a ride to get my car. Broke my Craftsman digital torque wrench doing my wife's Charger RT Road & Track's rear brakes. I'm still a lucky guy.

The shop said the A/C system was empty.(?) They charged the system with R134a and dye, but couldn't find any leaks. They advised keeping an eye on it for the next 2 -3 weeks.

My questions are what was the static pressure of 85-100? Air? Why did the compressor seem to come on? I heard the click of engagement.

Yadkin
05-25-2017, 04:19 PM
Before I refill an AC system I always like to change out the O rings. It's the most common area to leak, they are cheap and easy to replace.

Deanj
05-25-2017, 07:54 PM
I'm sure I'll find out during the summer. The dye should show up.

Not to change the subject, but driving in the rain led me find the truck floor with pools of water. Like someone poured 6 ouches on each side of the spare on the flat floor. No real suspects from inspection.

Dean