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New compressor, etc but still not cold. 1968 Olds

amphicar770 on Wed August 12, 2015 4:49 PM User is offline

Year: 1968
Make: Olds
Model: Cutlass
Engine Size: 350
Refrigerant Type: R12
Ambient Temp: 94
Pressure Low: 55
Pressure High: 210
Country of Origin: United States

Hi All,

Hope the experts can help.

Recently replaced the compressor on my 1968 Cutlass Vista Cruiser with a Pro6Ten. At the same time I replaced all the hoses with new, removed and flushed the condenser which was pretty clean, new expansion valve, new drier, and a cleaned calibrated POA valve from one of the classic air places. I changed the oil in the Pro6Ten to mineral oil. I am using R12. It is charged with 4 lbs as measured on a refrigerant scale.

My vent temps are still not much better than about the low to mid 50's. A few notes (which hopefully help rather than bias).

The first POA valve I received was filthy. Seems like a core got mixed in with the "rebuilt" units. I contacted vendor and returned it, they sent it back supposedly cleaned and calibrated. It was still not as spotless inside as I would have expected but seemed OK. The initial error does make me wonder how careful they are about cleaning and calibrating or if I could have gotten it back set to R134. Maybe I should have used the original which did not look bad.

A stupid mistake on my part after reading the factory shop manual. The first time I charged it I did so as liquid (30 lb drum upside down). I wound up having to reclaim and recharge again, this time from the gas side (canister up). While compressor makes no strange noises of any sort, I suppose it is possible that I mucked something up.

I am thinking that the low pressure side whole be closer to 30 but it been closer to between 55-60. High side of around 210 seems about right?

Any ideas or help greatly appreciated.


Edited: Wed August 12, 2015 at 4:50 PM by amphicar770

ice-n-tropics on Wed August 12, 2015 5:36 PM User is offline

Yea, replace w/ the OEM POA
The bogie for outside air is 55 F at 55 mph 95 f and 50 percent RH
For 100 percent recirculation it's 45 F
GM/Harrison designed for 30 percent outside air in max mode to accomodate cigar smoking engineers + the heater leakage! The Japaneese gave GM a wake up call to 100 percent OSA. The Germans still think their tight cars need outside air for safe O2 ( Frankfurt/Munich/Suffenhausen/Wolfsberg still think they are superior engineers, but repair is a POsnot)
My test method is to tape the gages to the windshield (after poping the wiper fuse) and test driving to record pressures with thermostat in the center louvers only
I usually tricked the outside air door by placing cardboard between the appropriate contact points in the control head to keep the OSA door closed and get 45F
Many old car wrench heads just rip it out and install Vintage Air their selves for a 1/3 parasitic power reduction. Is TRB a distributor yet?
John 3:16 For God so loved ice-n-tropics etc.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Wed August 12, 2015 at 5:49 PM by ice-n-tropics

mk378 on Wed August 12, 2015 7:36 PM User is offline

Make sure the TXV sensor bulb is properly attached and insulated from external heat.

Put the interior fan on low or disconnect the wire to kill it entirely. The low side should drop and regulate itself at around 25. If it does not, your POA is probably not working properly. They can be tested off the car fairly simply with compressed air.

amphicar770 on Wed August 12, 2015 8:10 PM User is offline

Thanks. I will try the suggestion with the interior fan tomorrow

The bulb is secured and well wrapped with presstite tape. The thin copper pipe on the replacement was much longer than original. I coiled it and wrapped that in prestite tape as well.

Note that the POA is original style, probably oem, not one those aftermarket "poa replacement kits". That said, I still have doubts if it was actually really refurbished or calibrated properly. I still have the original unit I took off the car with the 1968 date stamp so, if I have to go through the process again, I will likely test and reuse that one.

I am guessing that the compressor itself is fine based on the quiet operation and decent high side pressure? Also assuming that using the Pro6ten in place of the original A6 should not significantly change R12 capacity. Also, for what it is worth, system was properly vacuumed and nitrogen purged using high quality Yellowjacket pump and gauges.

Dougflas on Wed August 12, 2015 10:42 PM User is offline

If you're running R12 with a POA, disconnect the blower motor. The low side should run at 30 psi

amphicar770 on Thu August 13, 2015 4:18 PM User is offline

Ok, when I turn the blower motor to low (which is off or darn close to it) the low side indeed drops to between 25-30, high side drops to about 175. Vent temps still around 55 with ambient temp of about 90.

amphicar770 on Thu August 13, 2015 9:26 PM User is offline

Hi All,

So, if pressures with fan off seem normal (I think they are), it is obviously something else.

Any ideas? Tomorrow I will try clamping off the heater hoses in case warm air is mixing with the cool. This evening I noticed the vacuum hose at the shut off valve was a bit cracked right where it connects. Snipped off the end and put it back on but have yet to do any further testing.

Based on pressures, does it seem like anything else I should be checking?

Thanks again.

Dougflas on Fri August 14, 2015 1:03 PM User is offline

Originally posted by: amphicar770
Ok, when I turn the blower motor to low (which is off or darn close to it) the low side indeed drops to between 25-30, high side drops to about 175. Vent temps still around 55 with ambient temp of about 90.
make sure your gages are zero'ed out. Look at the blend doors, heater reheat. I used to be happy if I got 48* vent temps 1200 rpm engine speed with a 20 inch bow fan in front of thr grill/

amphicar770 on Fri August 14, 2015 2:48 PM User is offline

I clamped off the heater hose but no real diff.

Took her for a drive. Mostly around 55 vent temp. As low as 49 at cruising speed, as high as 60 at stop.

Fan clutch is new and the fan moves a lot of air.

I could do a new condenser and evaporator. I don't mind doing it right but also do not want to just throw parts at it to no avail.

I'm stumped so welcome any ideas.

Thanks again.

bohica2xo on Fri August 14, 2015 5:55 PM User is offline

What engine speed are you using for this testing? is this idling in the driveway?


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

amphicar770 on Mon August 17, 2015 11:13 PM User is offline

I brought it up to about 2000 RPM. Yes, sitting in driveway. As noted, vent temps are meh even at cruising speed.

I've kind of given up for the moment. Possible next steps.

Open up evaporator box to remove that and any possible 47 year old accumulation of crud, new seals etc. Will test the rebuilt POA valve at same time in case it was calibrated for R134.

Moving the vent levers is sounds like all doors and flaps are closing. However, I read elsewhere that the foam/rubber seals deteriorate and may need replacing. (although I would think clamping heater hose would identify any problems here).

Considering an auxillary pusher fan in front of the condenser. There is room for one although I really do not think airflow is the issue as the mechanical fan really pulls a lot of air even at idle.

I could switch back to an A6 compressor. Not sure if there is any loss in capability using the Pro6Ten

Getting to the drier on this car is a major PIA. If I open system up again, will likely replace that again but likely need to pull the radiator to get access to the condenser, access to the drier. As noted earlier, if I am going to do that then it is tempting to put in new condenser and evaporator but do not want to throw parts at it if no diff.

Some have implied that on these older A-bodies that vent temps of 50 are as good as it gets. I find that difficult to believe running R12. Heck, when I rebuilt the AC on my '74 Porsche 914 I now see temps in the 30's.

Open to other ideas.

Thanks again.

bohica2xo on Wed August 19, 2015 1:33 PM User is offline

Cleaning the evaporator air side and making sure the seals and doors are working properly is a good plan.

You have replaced a 12 cid compressor with an 8 cid unit. It must turn 1.5 times as fast as the OEM A6 to move as much refrigerant. Keep in mind that a POA valve works best when the compressor can "outrun" it. 5 psi between the POA and the compressor is common. Iced up suction lines were common on A6 / POA systems.

Put the car in 2nd & go for a ride. Cruise @ 3500 engine rpm for a little bit and see what the cooling is like. After a few miles @ 3500, stop and check the suction line temp...


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Dougflas on Thu September 17, 2015 2:31 PM User is offline

I agree that checking the seals is a good plan. You may have air blowing around the evap instead of thru it. 48* right passenger duct 1200 to 1500 rpm with a box fan was what I used to achieve. Another commom problem was the oil bleed line which connected to the POA would plug up. Just something to check while system is open.

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