Ac High/Lows and not much cold blow

vin_vl29u · Apr 20, 2014

working on a 69 satellite 318 with stock a/c. Anyone know the ballpark pressures? Playing with it this morning (80 degrees, 10% humidity) the pressures were 120/35 and center blower temp 50 degrees (high blower speed) at high idle windows open. Not great but liveable. After a long drive this eve, 120/60 psi (90/15%) center vent 65. Get the same temp going down the freeway 75mph.

So basically once everything been sitting in the sun all day, temp in car around 115 at 5pm (i'm in phoenix), the a/c really lays down. I replaced the drier and expansion valve, since the car sat for about 8 years. Airflow doesn't seem to be an issue since the output temp doesn't change going down the freeway. So is it just a tired old compressor and is it worth rebuilding or just replace it ($150). I'm fairly good with a/c systems, but never rebuild the old vtwin. Thanks for any input.

vin_vl29u · Apr 20, 2014

Part 2, thinking about that valve on the suction side. What's it called and could this be part of the problem. I know I've 'cleaned' one once and restalled it and the system worked, but was on a 1972. Does the 1969 use one?

cdr · Apr 21, 2014

check & make sure the heater valve is shutting off.

vin_vl29u · Apr 21, 2014

cdr said:
check & make sure the heater valve is shutting off.

That's what I thought it was at first, so I bypassed the heater/vavle.

68GTX440 · Apr 21, 2014

How is the cycling of the compressor? at about 2000 rpm's how many times does it cycle on and off. <Per minute.
If your pressures are ok and you have about 3 cans of freon in your system (if using cans) the cycle switch should not deactivate the clutch until around 34 to 40 degrees or so.
If it is cycling to much if you remove the cycle switch from the mounting surface and carefully turn it over you may have 2 small holes right around where the wires hook up. You can adjust the cycles of the compressor here.

For your high side take the ambient "outside" temp multiply by 2 + 10% and your high side should be in that range.
( say it is 100 deg where you are X2 =200 +10% = 220 = Normal High side psi)

On older Chrysler products the low side should be between 15 to 30 psi @ approx 2000 rpm.

vin_vl29u said:
That's what I thought it was at first, so I bypassed the heater/vavle.

vin_vl29u · Apr 22, 2014

68GTX440 it never cycles, I've even unplugged the blower fan for a bit. Things get cold, nut never near freezeup. The only controls are the dual cap expansion valve and the little mystery valce (EPR, which I just found the name of). The system is full of r12, 45oz or so, still has the little sticker giving the capacity. Forgot to add, that the a/c controls are all bypassed, I just have the blower and a/c clutch hooked up to a switch and relay till I get a new controller. I do have vent doors in the right position.

Thankfully just found my Mitchell a/c manual and found the name of the epr valve. The old expansion valve had some crud in it, so hoping the screen or epr is plugged up. Will play with it tomorrow, summer is coming.

bigblock · Apr 23, 2014

The high side pressure is too low. What does the sight glass look like? Should be clear if the system is full and operating. See bubbles?Add freon.

vin_vl29u · Apr 23, 2014

I think I found the problem, the screen in the suction line was plugged up with some black gunk and half collapsed on itself. Kind of looks like coffee grinds or ground up charcoal. Reminds me of carbon you scrap off old pistons. Maybe the old drier was breaking down. I'll try soaking it in some pb blaster, I've had good luck in the past with crud/rusty parts. I tried looking for a new screen, but can't find one. Plus I can't get the thing out (don't want to tear it up if I can't get a new one), so just soaking the whole fitting. The epr valve looks fine. Reading online, most people remove it and just go with a thermostatic switch to keep the evap from freezing. Suppose to be a must if you're going to 134a.

Just reading up on the black stuff, couple sites call it the black death. Water getting into the system and breaking down the oil. Sounds like more fun.

vin_vl29u · Apr 23, 2014

Working good, saw 34 degrees center vent high on high going down the road. Cleaned the screen, flushed the evap and condenser and added some new oil. It was only 85 outside and it was getting dark, will check it during the day. Thanks all.

68GTX440 · Apr 24, 2014

Yup the old dryer was the culprit. They do have like a charcoal substance inside them.
Great job on the find.......

vin_vl29u said:
I think I found the problem, the screen in the suction line was plugged up with some black gunk and half collapsed on itself. Kind of looks like coffee grinds or ground up charcoal. Reminds me of carbon you scrap off old pistons. Maybe the old drier was breaking down. I'll try soaking it in some pb blaster, I've had good luck in the past with crud/rusty parts. I tried looking for a new screen, but can't find one. Plus I can't get the thing out (don't want to tear it up if I can't get a new one), so just soaking the whole fitting. The epr valve looks fine. Reading online, most people remove it and just go with a thermostatic switch to keep the evap from freezing. Suppose to be a must if you're going to 134a.

Just reading up on the black stuff, couple sites call it the black death. Water getting into the system and breaking down the oil. Sounds like more fun.

bigblock · Apr 24, 2014

You better flush the system before it kills the compressor. And add a new receiver dryer.

vin_vl29u · Apr 27, 2014

bigblock said:
You better flush the system before it kills the compressor. And add a new receiver dryer.

I flushed it out after finding the black junk. The drier had like 10 mins of running. I'll just run as is and if it starts getting noisy, I'll replace the compressor and flush it out again. Could use some new hoses anyone, they look original

Ac High/Lows and not much cold blow

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