'67: here's a ? for you A/C experts out there.

[Barbara S.]

I'm in the process of trying to get my A/C system up and running for my '67 coupe. It has factory A/C. Here's my problem:

My A/C pump won't pump down. The low side only goes to 95 lbs and my high side only goes to 105 lbs. I've tried it with two rebuilt compressors, but the same result each time.

What is causing my system not to pump down? On a day like today (85 degrees), my low side should be around 36 lbs and my high side should be around 280 lbs. I can't believe that it's my pump because I've tried two separate rebuilt pumps. I have all new hoses and a new expansion valve. What, besides a bad pump, can prevent my A/C system from pumping down?

Any suggestions? I'm all ears!
Tony

[Tracy C.]

[Wayne W.]

Re: '67: here's a ? for you A/C experts out there.

Holy Crap, at 85 deg. who needs AC. The `67 didnt have an expansion valve, but has a POA valve. My opinion that will probably be the source of the problem.

[Barbara S.]

Re: '67: here's a ? for you A/C experts out there.

Wayne. Yes, there is both an expansion valve and a P.O.A. valve with a '67 A/C system.

The 85 degrees is a nice relief, but the judges might like to see that it works! :-)
Tony

[Dick W.]

Re: '67: here's a ? for you A/C experts out there.

What is your RH duct temperature with air on max? I would look for

[Barbara S.]

Re: '67: here's a ? for you A/C experts out there.

Not there yet, Dick. I'm trying to charge my system. Just got the rebuilt compressor back from the rebuilder and trying to get the R12 in. It won't pump down.

Tony

[Wayne W.]

Re: '67: here's a ? for you A/C experts out there.

Oops I guess it does have one down there, shows how much trouble I have had with the two that I have.

[David M.]

Re: '67: here's a ? for you A/C experts out there.

You definately have an obstruction some where. 95lbs on the low is way out of spec. First, anytime you open the system the dryer desiccant MUST be replaced and the system needs to be evacuated a minimum of 30 minutes, preferably 1 hour. Did you have a catastrophic failure of the pump that could have sent trash into the system? If so the entire system needs to be cleaned and purged. You should have a POA not an STV. 66 was the last year for the STV(suction throttling valve). Your problem will be in one several areas. First the simple things. Is the clutch slipping on the compressor, sorry had to ask. One of the remaned hoses may have an obstruction from the crimping procedure to install the hose ends, seen that one before. Or a chunk of hose got loose and is caught in one of the 2 filters. The pilot operated absolute valve(POA)has a screen on the inlet side where trash will gather, pull the inlet line and look. Is there any evidence of corrosion or crystalization of salts on either end of the POA? That means moisture got to the POA and has most likely caused damage internally. Replace it or get an eliminator kit and eliminate it. I'm not sure if you will have an externally or internally regulated expansion valve but in either case its critical that this device works. Its job is to pass the refrigerant through its metered orifice where it changes(restricts) high psi liquid to a low psi liquid. This orifice is critical and the smallest debris can cause the problem you describe. There is a filter screen on its inlet side that you need to inspect for debris. The expansion valve is more sensitive to foreign materials than anything else in the system. You said you replaced the expansion valve. It is critical that it be replaced with a comparable valve. There is a number on it that corrsponds to the orifice size. If its orifice either too small or large it will cause the symptoms you describe too. Classic Auto Air(dot com) will have what you need including the eliminator kit I mentioned as well as more information if needed in regards to the expansion valve compatibility. Good luck hope this helps.

[Larry S.]

Re: '67: here's a ? for you A/C experts out there.

I am not expert but I may be able to help

You may have to give more information

The pressure your giving sound like the compressor is not running, and all that your reading is a static charge that you have in the system. That's why the two pressures are almost equal.

When I hear the term "pump down" ,
Its a term we use when we want to work on a residential or commercial A/C system. You close off the high side king valve and use the compressor to pump the refrigerant into the condenser coil,once the suction line goes into a vacuum you close off the suction lines king valve. Now you recovery what little is left in the refrigerant lines and evaporator coil so you can work on them.

So please elaborate what your trying to say

With the gauges in your hand (not connected to the car) what are your gauges reading. Is the blue gauge (low side)showing slightly in a vacuum or the red gauge (high side) showing slightly over O psi you can zero them out with the little tiny screw under the plastic lenses should both be at zero before you start. I think one of them is reading low or high and that's why you have a 10 psi pressure difference when your connected to the car.

With the car off and the gauges attached what are your pressures? This is the static charge

With the car on and the compressor engaged what are your pressures?

Can you see or hear the compressor come on ? you have to hear that snap of the compressor clutch engaging and then see or feel the engine drop down because it has a load on it from the compressor.

First confirm the clutch is actually pulling in and the compressor is running. Are all of the compressor you have been trying all ready have the clutch on them? or are you transferring the same clutch from one compressor to the next.

Good luck and I will be waiting on your reply

[Joe C.]

Re: '67: here's a ? for you A/C experts out there.

Tony,

So, you're not trying to evacuate the system, but trying to pump all of the freon into the reciever/dryer, right?? WHY, are you trying to pump the system down?

I remember doing this with the A/C systems on the NYC subway cars, while working for TRANE Corp. while in college. I did not realize that automotive systems had this capability. Did you install extra valves on the hi and lo side? I vaguely remember shutting a valve on the low side first, then running the system until the pressure drops, then closing the high side, finally shutting the system down. Am I on the right track?

If this is, in fact, what you are trying to do, and you have the necessary hardware in place, then in addition to a faulty compressor, any leaks in the system will prevent this from being accomplished. Also, if you have not evacuated the system first, then any entrained moisture will freeze at the expansion valve, causing a restriction or obstruction. Finally, if excessive air (moisture) has entered the system, then the reciever/dryer wil have become saturated, causing a further obstruction.

You really should evacuate your system first, then replace the reciever/dryer with a new (dry) one, IF you have had the system "open" for a long period. After that, charge the system, and then "pump down" if you wish to.

Joe

[Norm C.]

Re: '67: here's a ? for you A/C experts out there.

Tony,,,, who did you use for the reconditioning of the pump? Thanks for your help!!

[Barbara S.]

Re: '67: here's a ? for you A/C experts out there.

It was restored by a company called Classic Air out of Tampa. They were recommended on this board.

Thanks.
Tony