67 AC WONT COOL, BELT SQUEELS

[Bob C.]

Hope you guys can help. My 67 conv, 427/400 factory ac, running on r12 has 2 maddening problems with the ac.
1. Cools poorly...always has an outlet temp of 55 to 60 degs.
THE HISTORY
I bought the car @ 5 years ago, ac was poor at that time, was filled with r12.
It had an "update valve in place of the POA valve--- a hollow tube--- how stupid is that? I replaced the update tube with a correct POA from Old Auto Air Products as well as having them rebuild the reciver/dryer. Evacuated and charged the system with 3.0 lbs of r12. No improvment. Increased the charge to 3lb 4 oz r12. No improvment. At this point the pressures were @ 200 and 30 psi @ 75 deg.. The sight glass was full of bubbles so I charged it with another @ 8 oz until the bubbles were almost gone. No improvment. The pressures at this point were @ 250 and 40 psi.
Next step...
I removed the evaprator cover and made sure the unit was sealed in its housing.
The evaprator was a GM unit date coded 1981 and was a perfect fit. I sealed it ever better than GM did. I replaced the expansion valve at this point with a new unit from Classic Auto Air and replaced the hot water valve, even though the old one sealed properly. I also rechecked the vaccum operation of the hot water valve again--- working correctly.... still no improvment. I am ASE certififed in this stuff and I am stumped. Wrong expansion valve ??
P.S. I also had the compressor tested by Old Auto Air... "pumped" just fine.
P.S. When you read the other problem below, the squeeling belt is not the problem. It does not slip at 1500 rpm where all of the above specs came from.

2. The Power steering belt slips with the ac on.
As you guys know the 427 only ran a rather strange drive belt configuration.
There is a non adjustable idler between the crank and the water pump... It is tight.
There is a power steering belt from the crank to the water pump to the power steering pump.
There is a belt from the popwer steering pump to the alternator.
There is a belt from the water pump to the ac compressor.
At speeds of over 2500 rpm the power steering belt slips and squeels when the ac is on. It appears the power steering drive belt can't run the load of the alternator and ac compressor.
Have tried the following with no real improvment...
1. Checked the wear on all pullies and checked the dept of the belt in the pullies---ok.
2. Tried wider power steering belt.
3. Over tightened belts.
4. Double checked alignments.
Again--- I am out of answers. This winter I intend to remove the crank pulley and install a third pulley the same size as the existing 2. This way I can run the ac belt from the crank to the water pump and ac compressor.
Any help would be greatly APPRECIATED. God bless the U.S.A. and Chevrolet.

[Joe C.]

Re: 67 AC WONT COOL, BELT SQUEELS

Bob,

Some questions:

What is the temp of the evaporator? Is it icing up? Does the compressor "cycle" as it should?
Why do you question the expansion valve? Is it the right one, or not? If not, then you can be sure that that is the problem. They aren't a "one size fits all", and the orifice should be matched to the system. Is the POA valve the right one?
Check your service manual to see what the max. charge is required for your sealed system. If overcharged, then the head pressure will be excessive, and you will damage the compressor.
If you indeed, have overcharged the system, then the compressor is laboring under high loads, and creating a drag on the water pump pulley. This may seem like the PS pump, but both are driven by the crank pulley. My vote goes to excess head pressure in the compressor. If you don't know the history of the system, maybe there is "trash" in one of the lines, causing a restriction.

I would verify that all is as it should be, before looking to modify anything.

Joe

[Jack H.]

What would make the compressor 'cycle'... *NM*

[Jack H.]

What would make the compressor 'cycle'... *NM*

[Joe C.]

Re: What would make the compressor 'cycle'...

Jack,

Yes, no cycling with POA valve(suction throttling valve), as in systems employing orifice tubes.

Joe

[Joe C.]

Re: What would make the compressor 'cycle'...

Jack,

Yes, no cycling with POA valve(suction throttling valve), as in systems employing orifice tubes.

Joe

[Bob C.]

Re: 67 AC WONT COOL, BELT SQUEELS

HI Joe
The evaprator does get cold from the expansion valve thru the poa all the way back to the compressor. It will not develop frost, just lots of sweat. It is hard to get an exact temp, my small thermoteter slid under the anti sweat tape reads usally @ 50 deg. My infrared tends to be all over the place due to engine compartment temps, but usally in the 45 to 50 deg rangs--- a long way from frost.
Both the poa and expansion valves are new or reman. I am at the mercy of the vendor to be sure they are right, but they have lots of experence with older systems. I think, however it wont hurt to speak with them again and possibly send both units back for testing.
The max head pressure I have seen from the compressor is @ 275 psi on a real hot day with the engine fully up to temp. All testing is done at 1500 to 2000 rpm.
I have seem 2 different charge weights from the 67 gm service manual, 3.0 lbs and 3 lbs, 4 oz. I have tried both with no real difference in temps. only the expected slight rise in high pressure readings. With either charge the sight glass is full of bubbles.
I don't belive a restriction in the system is too probable, the reciver dryer and expansion valve are new or rebuilt and that would usally trap any particles in the system. Also a system that is severly restricted will run low pressures on the low side and sky high pressures on the high side.
It is the power steering belt that squeels, it drives the water pump pulley that in turn drives the ac compressor. Weird, I know but that is what gm did.
THANK YOU for taking the time to give me your thoughts.
When these 2 problems are corrected I will be sure to post what iI found for the next guy to consider.
Bob.

[Bob C.]

Re: 67 AC WONT COOL, BELT SQUEELS

HI Joe
The evaprator does get cold from the expansion valve thru the poa all the way back to the compressor. It will not develop frost, just lots of sweat. It is hard to get an exact temp, my small thermoteter slid under the anti sweat tape reads usally @ 50 deg. My infrared tends to be all over the place due to engine compartment temps, but usally in the 45 to 50 deg rangs--- a long way from frost.
Both the poa and expansion valves are new or reman. I am at the mercy of the vendor to be sure they are right, but they have lots of experence with older systems. I think, however it wont hurt to speak with them again and possibly send both units back for testing.
The max head pressure I have seen from the compressor is @ 275 psi on a real hot day with the engine fully up to temp. All testing is done at 1500 to 2000 rpm.
I have seem 2 different charge weights from the 67 gm service manual, 3.0 lbs and 3 lbs, 4 oz. I have tried both with no real difference in temps. only the expected slight rise in high pressure readings. With either charge the sight glass is full of bubbles.
I don't belive a restriction in the system is too probable, the reciver dryer and expansion valve are new or rebuilt and that would usally trap any particles in the system. Also a system that is severly restricted will run low pressures on the low side and sky high pressures on the high side.
It is the power steering belt that squeels, it drives the water pump pulley that in turn drives the ac compressor. Weird, I know but that is what gm did.
THANK YOU for taking the time to give me your thoughts.
When these 2 problems are corrected I will be sure to post what iI found for the next guy to consider.
Bob.

[Jack H.]

Re: 67 AC WONT COOL, BELT SQUEELS

Your copy of the '67 AIM cites factory AC test specs on UPC C60, Sheet E10 (freshly started engine at 2000 RPM). Plus, the Chassis Service Manual should provide a fuller dynamic profile of AC system specs.

My copy of the '67 AIM is badly photocopied making the test table rather illegible. But, from my copy of the '65 AIM (specs should be roughly equivalent) the data is:

Engine RPM: 2000
Air Temp: 70, 80, 90, 100
Head Pressure: 150-170, 175-195, 200-220, 240-260
Evap Pressure: 28 PSIG
RH Outlet Discharge Temp: 36-40, 36-40, 38-42, 39-43

A frequent Achilles' Heel issue on these classic cars is the evaporator core being 'plugged' with road debris (leaves, dirt, Etc.) from prior use that DRAMATICALLY reduces air flow and heat exchange in the air box plenum...

[Jack H.]

Re: 67 AC WONT COOL, BELT SQUEELS

Your copy of the '67 AIM cites factory AC test specs on UPC C60, Sheet E10 (freshly started engine at 2000 RPM). Plus, the Chassis Service Manual should provide a fuller dynamic profile of AC system specs.

My copy of the '67 AIM is badly photocopied making the test table rather illegible. But, from my copy of the '65 AIM (specs should be roughly equivalent) the data is:

Engine RPM: 2000
Air Temp: 70, 80, 90, 100
Head Pressure: 150-170, 175-195, 200-220, 240-260
Evap Pressure: 28 PSIG
RH Outlet Discharge Temp: 36-40, 36-40, 38-42, 39-43

A frequent Achilles' Heel issue on these classic cars is the evaporator core being 'plugged' with road debris (leaves, dirt, Etc.) from prior use that DRAMATICALLY reduces air flow and heat exchange in the air box plenum...

[Jack H.]

On belt squeal...

Factory original v-belts were SAE dimensioned and cloth wrapped sitting fully down within the pulley pathways. Service replacement belts were of die-cut construction and metric dimensioned. The 'equivalent' replacement belt is wider and therefore longer causing it to ride higher on the pulley grooves.

I don't think too much of the current reproduction cloth wrapped belts (they've got a reputation for short life/breakage). But, NEITHER the repro nor a correctly sized service replacement belt should be squealing under normal operation UNLESS one or more pulleys aren't correct or there's belt path mis-alignment (excessive side loading).

[Jack H.]

On belt squeal...

Factory original v-belts were SAE dimensioned and cloth wrapped sitting fully down within the pulley pathways. Service replacement belts were of die-cut construction and metric dimensioned. The 'equivalent' replacement belt is wider and therefore longer causing it to ride higher on the pulley grooves.

I don't think too much of the current reproduction cloth wrapped belts (they've got a reputation for short life/breakage). But, NEITHER the repro nor a correctly sized service replacement belt should be squealing under normal operation UNLESS one or more pulleys aren't correct or there's belt path mis-alignment (excessive side loading).

[Jim T.]

Re: 67 AC WONT COOL, BELT SQUEELS

Bob in reading about what you have done, did you keep the old expansion valve? If you did, did you remove, or can you now remove the inlet screen and examine it for trash? This is a very small screen, I removed mine using an easy out with only finger power to pull it out. Mine was full of trash from a ruptured dryer desiccant. You mentioned removing your dryer and having it rebuilt, was the dissicant bag ruptured? The desiccant will flow through your condensor and could of clogged up your new expansion valve reducing/preventing flow even after installing the rebuilt dryer. It is possible that the rebuilt dryers desiccant bag ruptured. Hope you find your problem. The expansion valve screen used to be available from parts stores years ago, bought one in 1988.