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No low pressure reading


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mrmustang
Novice

Aug 18, 2016, 7:03 AM

Post #1 of 17 (759 views)
  post locked   No low pressure reading  

I have a 1969 Mach1 Mustang with factory ac,351 with 85,000 miles. I tried to load freon but didn't have any reading on low side after loading freon.
I replaced the compressor,expansion valve,drier and condenser. Still no low pressure reading.
Any thoughts about what is wrong??


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 18, 2016, 7:12 AM

Post #2 of 17 (756 views)
  post locked   Re: No low pressure reading  

Are you using original R-12? Either way which type of low and high side ports used on this? There were "stem valves" you need to open and close with a 1/4 square or possible Schraders. If converted you still could choose types of Acme, with Schraders on them or ones that rely on an OE Schrader valve.


Shown here if it shows.........

(1st didn't show. Just Google out images for pics of assorted uses for them by name could help)

If retrofitted you may need to adjust the adaptor's pin such that it does depress the OE Schrader or you get nothing. It might have taken refrigerant or not.


Other: It all leaked out as fast as you put it in so reads true and is zero! If so, find where,


T



(This post was edited by Tom Greenleaf on Aug 18, 2016, 7:14 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 18, 2016, 7:28 AM

Post #3 of 17 (752 views)
  post locked   Re: No low pressure reading  

New post in case you already read the other.


I'm having a hard time finding correct use and pictures of stem valves?
One here should show for sale..........

They came with an aluminum cover over the 1/4" square to operate those. Operated only when turned fully CC (counter clockwise) and serviced with it part open about a turn and a half reverse threaded! If you tightened those you could remove a compressor without losing refrigerant from the rest of the system - unheard of since about 1969!


Used later for non automotive purposes still A/C just not so much or at all in cars.
If you do NOT have this type at all forget all this. Need to know which as OE (you said which means ''Factory" to me as well) did use "stem valves" in Fords in 1969 - not guessing I owned one,


T



(This post was edited by Tom Greenleaf on Aug 18, 2016, 7:29 AM)


mrmustang
Novice

Aug 26, 2016, 6:21 AM

Post #4 of 17 (589 views)
  post locked   Re: No low pressure reading  

There is reading on the high side but the low side is sucking vacuum. How can you tell if the compressor is bad? I did put on a rebuilt compressor.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 26, 2016, 7:44 AM

Post #5 of 17 (586 views)
  post locked   Re: No low pressure reading  

What do you have here? There could be different OE parts for these one called "Desert Cooling" package or just different than I can just look up.


Do you have just the two ports, same threads with Schrader's or what? If you are getting any readings something is going on.


This should almost certainly have a sight glass so takes guessing out for how much to charge but still note pressures and all conditions when charging a system.


You need to say - are you equipped and know what to expect for temperatures at what pressures and pressures under what conditions?


Read this and see if it makes any sense to you as A/C then and worse now you still have to know what you are up to or will mess it up and yes even this you can blow a compressor fast doing things wrong.


Link is up top anyway but will post it - click > http://autoforums.carjunky.com/..._A/C_SYSTEMS_P45460/


All this info applies even to this car,


T



mrmustang
Novice

Aug 29, 2016, 6:28 PM

Post #6 of 17 (565 views)
  post locked   Re: No low pressure reading  

I consulted an AC man that I used before he retired. He thought that I have a bad expansion valve although I replaced it. He that if you put the bulb part in ice water the valve will close and you can't blow through it. I could blow through it when it was warm and after submerging the bulb in cold water could also blow through it. I bought 2 expansion valves at the same time and this was the 2nd one not the one on the car now.
So I presume this valve is bad?


Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 30, 2016, 1:39 AM

Post #7 of 17 (554 views)
  post locked   Re: No low pressure reading  

? Yes they sense temp and determine flow as you described.
What is in it now a working one and properly in place or what? Is this all set now?


Lost you somewhere with where you are at with this,


T


PS w fun facts: This was the last model year (I think) for Mustangs to use 6v dash controls not the issue at hand but should know that. It's ballasted voltage down partly. Shouldn't be for anything A/C. Part lost as most serious "sports cars" would not have A/C on purpose - an invasive and very costly option new for a car that was mostly about being a muscle car not a luxo boat of the time. It's essentially a Falcon's last fundamental body designs altered enough up to too much for the power options available for the day. Super popular cars then and now, Tom



Discretesignals
Ultimate Carjunky / Moderator
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Aug 31, 2016, 4:08 PM

Post #8 of 17 (525 views)
  post locked   Re: No low pressure reading  

What is the static high and low side pressure readings on your gauges when the compressor is not engaged? If the compressor was bad, the high and low side pressures would be the same or close to it with the compressor running and a full charge in the system.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Aug 31, 2016, 4:10 PM)


mrmustang
Novice

Aug 31, 2016, 4:36 PM

Post #9 of 17 (519 views)
  post locked   Re: No low pressure reading  

When the compressor was running it was actually drawing vacumn on the low side. I've been told that this indicates a bad expansion valve?


mrmustang
Novice

Aug 31, 2016, 4:37 PM

Post #10 of 17 (518 views)
  post locked   Re: No low pressure reading  

The expansion valve is new.


Hammer Time
Ultimate Carjunky / Moderator
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Aug 31, 2016, 4:55 PM

Post #11 of 17 (515 views)
  post locked   Re: No low pressure reading  

Why son't you answer the question DS asked you. What are the pressures before the car is started?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 31, 2016, 4:55 PM

Post #12 of 17 (514 views)
  post locked   Re: No low pressure reading  

What are your high and low side pressure readings? Do you have a full system charge in the system?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


mrmustang
Novice

Sep 1, 2016, 5:26 PM

Post #13 of 17 (501 views)
  post locked   Re: No low pressure reading  

I think the high pressure was 115 and the low pressure was actually pulling vacumn on a full charge.


Hammer Time
Ultimate Carjunky / Moderator
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Sep 2, 2016, 3:33 AM

Post #14 of 17 (492 views)
  post locked   Re: No low pressure reading  

That sounds like either a low charge or a restriction.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Sep 2, 2016, 4:33 AM

Post #15 of 17 (487 views)
  post locked   Re: No low pressure reading  

Sorry if I missed it but what type service ports and refrigerant are you using?
Again - if stem valves generally like this..........

Another showing what is going on inside this thing helps a lot to understand...........

Is it this type now? Have to know. Also called "Isolation Valves" shown like this..........



This type the left of picture would have a screw on cap, right to line, bottom to compressor. With the 1/4" square turned CC (counter clockwise you can operate the system but can't add or read pressures. Any leakage it would confuse all readings or leak charge out. The port point right at us in that is the standard port without a Schrader valve for your gauges and to add or vacuum system. Same size and type both high and low side.


That type you turn the 1/4" stem in part way to service. That position is to add refrigerant, check pressures at all and system would operate with partial restriction when there to some degree. If you kept tightening you've isolated the compressor from the whole system and could remove it totally leaving remaining "Freon" in the system - do you follow me at all?


Repeat! If that type and you didn't have it in proper position you never added enough refrigerant and if not watching pressure when in right position it's a restriction by itself by design.


System capacities from memory as I can't look it up as you haven't said what you have or gas you are using. It could really hold up to FIVE pounds of refrigerant on some OE designs, all done to OEM specs.


This compressor should (could be an alternative) look a lot like a small lawn mower engine and really have a piston like an engine to pump.


Sounds like something is wrong normally.


OE has a sight glass so take guessing out for charge but if you don't have service ports in correct position nothing means anything about pressures, operation, sight glass or anything about it.


If this type and totally confused just send the vacuum and charge out to be done as you'll just waste untold amounts of refrigerant and blow the compressor which you may have already done - brand new, rebuilt or whatever you have,


Tom
(edited twice now) (3rd time now w new pic) If this type and no help or understanding for automotive A/C of the vintage this was still used on heat pumps for homes, buildings, walk-in refrigeration rooms up to even just about 10 years ago if not still?)
(4th edit to add pictures of the ports and how they work the best I could find)



(This post was edited by Tom Greenleaf on Sep 2, 2016, 7:37 AM)


mrmustang
Novice

Sep 11, 2016, 12:35 PM

Post #16 of 17 (421 views)
  post locked   Re: No low pressure reading  

Replaced the liquid line and that solved the problem.
Thanks to all that replied!!!!


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 11, 2016, 1:31 PM

Post #17 of 17 (419 views)
  post locked   Re: No low pressure reading  

Glad you found it and could fix it so fast actually. I'll close out thread as solved. YOU can ask to re-open it upon request,


T







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