Ac problems

[William F.]

Need advice from you AC experts.
When Ibought my'67 with factory R12 C60 system in 2010, wasn't cooling. Found bad POA. Rather than buying a POA which may or may not work long, replaced POA with "POA upgrade" essentially a pressure reading tube and switch that cycles compressor on and off. Everything great till recently when sometimes long sometimes short cyclying. Old Air products said to replace just the switch. Did this and cyclying about right in length of time and pressures but won't produce vent air lower than 50 even though return "pipe" with the capillary tube attached is cold. Heater valve is not stuck open. Turning adjustment screw on switch doesn't help.We checked pressures before replacing the pressure reading electrical switch and seemed ok on freon but I can see bubbles in sight glass when compressor cycles on and off. Just low R12? I know proper way to check is to pull R12 from system and see if proper 3 lbs 4 oz weight, but OK if I just attach a can of R12 and watch vent temp as I add to see if low R12 is the problem.
Thanks for staying with me on this lengthy thread.

[Domenic T.]

Re: Ac problems

William,
To cycle a A6 is a sure way to end it. They were not designed to be cycled. I can tell you that I saw what it did to the clutch and pulley which caused a leak because the metal to metal clutch won't always center at higher RPM's. This causes the shaft to vibrate and the 2 part ceramic seal to not center as one part of the seal is attached to the shaft and the other half to the case front cover. Also the roller bearing life and shaft will be short.

Dom

[William F.]

Re: Ac problems

I'm sure you're correct Dominic and may go back to POA system in the future, but just trying to just get system I have right now cooling for at least part of this summer.

[Domenic T.]

Re: Ac problems

William,
Not trying to bust a bubble. But what I saw was real. I did over 200 vette comps and have tried to improve the works. Years ago, you and others may know, that the evaporator would freeze and what we had to do was turn off the A/C and let it defrost.
I have written a few threads about ingaging the A/C. Personally in my vintage cars I do it before start so the clutch can center. The clutches were hand made and WAY out of wack. I run them on my lathe and they wobble. Some are OK, but most are way off.
Now the replacements are right on. BUT not cosmetic for judging. So back then when the A/C was not doing good, we turned it off and let the air blow thru the evap. That was sorta like a swamp cooler. when all ice dripped out of the tube we re-engaged the A/C. Now when I did that I did it by going to idle and engaging the A/C.
These newer units are made for the cyckled system. The A6 was not. Mostly because of the clutch!
Newer cars always defrost and you see it dripping. Not so back years ago, we had to do it by hand.
I just want yours to do what you want it to do. That's only my opinion on the old system, and I think it may be in the old operators manual?
Larry Mulder, (powershift) is expert on A/C, and he knows the system inside and out. All I do is make sure the A6 is good for years after restoration.

Dom

[Mark E.]

Re: Ac problems

Picking up on what Dom suggests, go back to the original POA set up. Have yours rebuilt or find an NOS.

[William F.]

Re: Ac problems

How about some help on how to get what i have now working right.l Would you please reread my original thread and advise about whether I have low R12. Also how cold is the metal pipe on the outlet side of the evaporator core where the capillary tube is attached supposed to be?
Dominic, I never had the freeze up problems you described in the 66's factory ac systems when those cars were new.
Larry, M., please give me some advice.
thanks

[Harry S.]

Re: Ac problems

Here are two to check.

1) Pull the view cap off the top of the drier. Run the system and check for bubbles. If you see lots of bubbles pass by you may be low on Freon.
2) You may have a hot water problem. Run the car till it gets to temperature. Use an IR gun and check the temperature before and after the hot water shut-off valve. The temp after the valve should be significantly cooler. If the temp is the same on both sides, the valve may be stuck open. You do not want hot water in the heater core. Make sure the heat lever is all the way in on the dash. Change the valve. It's about a 30 minute job to change the valve and an NOS one (if you can find one) will be about $150.00.

[William F.]

Re: Ac problems

Thanks but checked and no hot water entering heater core. I see some bubbles in sight glass when compressor cycles off and on. Looks clear (meaning full of freon or a void?) most of the time. Low R12? Just add a bit of R12 and watch dash outlet temps to se if it blows colder?

[Larry M.]

Re: Ac problems

Bill:

I do not know anyone who has successfully replaced POA with a pressure switch bypass. A number of folks have been successful with a bypass controlled by temperature, but not pressure. It seems the pressure switch is too sensitive and cycles the compressor very very frequently. Which as Dom says, is not good.

Having said that, there are three ways to diagnose your problem:

1. Assume refrigerant is low and add 1/2 a can to see if your cabin duct temperatures improve. Many of us did just this every year back in the 1960's to our AC cars. They always seemed to lose a 1/2 to 1 can annually. I would not add more than 1 can (or 12 oz.)

2. Check for bubbles in the sight glass. They appear when refrigerant is low. Add refrigerant until bubbles disappear and compressor is running (not off/idle). I found that after bubbles disappear, usually the correct amount of refrigerant is about one 12 oz can more.

3. Do the correct/proper thing and hook-up gages to the LO and HI side connections and read what the system is doing. Low refrigerant will usually show up as low pressure on the HI side and very low pressure on the LO side. Normal pressures at this time of year might be 29 psig on the LO side and 200 psig on the HI side..........so you would be much lower than these numbers when the system is running at 1500-2000 RPM.

Larry

[William F.]

Re: Ac problems

Larry et al
At wit's end. Pulled R12 out with vacuum machine. A little low so added about 6 oz. After recharging, At first cooled down but after running a while, compressor cycles but won't blow colder than 50:*. Before problem started would blow 38*-40*. Doesn't matter how I adjust adjustment screw on switch that reads pressure and tells compressor when to cycle off. I really don't think hot water is getting into heater core but may put a hot water cutoff valve into heater hose. . Could expansion valve be bad and causing this?
Thanks

[Larry M.]

Re: Ac problems

Bill:

Running your system with a POA/STV bypass using a pressure switch is problematic.........no one I know has been successful.

That being said, it is possible that the expansion valve is bad or that the sensing bulb is not attached or insulated correctly on the evaporator outlet tubing. If you changed out the POA bypass, you may have disconnected or adjusted the expansion valve sensing bulb. It also requires good insulation. The expansion valve could also be bad or inlet restricted with debris. The only way to troubleshoot is to have LO and HI side pressure readings at 1500-2000 RPM. Without this, we are just guessing or worse.

Is your expansion valve original?? Originals have built in inlet debris screens..........replacements often do not.

Do you see significant bubbles in the drier sight glass??

How often does compressor cycle in a 10 minute time period??

Are you doing the AC work yourself, or are you using a AC shop??

Larry

[David M.]

[Domenic T.]

Re: Ac problems

WILLIAM,
My best guess again is that your loosing pressure from the cycle during a cycle at cruising RPM. They slide off center causing a loss of pressure and oil. Hub clutches will not always center and vibrate the ceramic seal. The new replacement is right on as far a run out.
You cannot re-design the old system...
Why do you need to cycle ??
I have extremly unuasable pulleys and clutches from this.
I respect what larry says, but what you are doing is like asking a old man to try out for the 4 min mile.
Now, I hope I am wrong and between you and larry get this resolved.
I would put gages on and leave them on so you can see if you are loosing pressure during the cycle act.

Dom

[William F.]

Re: Ac problems

David,
I know what the blend door is but how do I get to it? Remove glove box door and get to it from there?
Thanks

[William F.]

Re: Ac problems

Dom,
I hear what you say but if you look in the '67 CSM you will see the Chevy "universal fit" AC systems, the under the dash ones used in Chevy 2's etc did cycle the A6 compressor with temperature, though not pressures. Did these compressors tear up prematurely?