1979 F150 will not cool below 60F register temps/evap partially warm

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jcamp2112
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1979 F150 will not cool below 60F register temps/evap partially warm

Postby jcamp2112 » Mon Aug 17, 2020 10:40 am

I've been working on this for 5 days now, i've reached the end of my AC troubleshooting knowledge. I need some real help now.

79 F150 460, just installed a whole new AC system, lines, york compressor, new evap, condenser, TXV, vacuumed it down overnight, and charged to spec. Calls for 2.75lbs of R12, so 80% of that is about 3 12oz cans of R134A. Issue is, no matter what I do, I can only get 60 degree vent temps. Only the bottom 10% of the evap gets cold. With a contact thermometer, the bottom of the evap is 30*f, and the top is 60f... Pressures are approx 10 on low side, and 150 on high side. This is with a garden hose on the condenser, so can rule out insufficient condenser airflow. I used a piece of paper to test evap airflow, and the paper clings to the coils when i let it go, so airflow over the evap seems normal. I Even changed the TXV last night just to see if it was that, and no joy. I've tried under charging it, over charging, no appreciable change really. The outlet of the TXV has frost on it, and like I mentioned, only the bottom 10% of the evap is cold and making conensation. This is all checked at the 1500rpm the manual calls for too.

The only constant in this is my vacuum pump. I notice last night, after a 10 hour pull down session, it only pulled the system down to -20inHg, I'm wondering if maybe there is excess moisture in there because the pump is failing? That's all I can think of at this point, but i'm open to suggestions.
I need help, I've reached the end of my troubleshooting knowledge on AC....

Edit: My stupid gauge isnt returning to zero, so thats why it's only showing 20 on vacuum., It is in fact pulling the system down to 30 inches if I account for the error in the gauge.
Last edited by jcamp2112 on Tue Aug 18, 2020 9:59 am, edited 2 times in total.
tbirdtbird
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Re: 1979 F150 will not cool below 60F register temps

Postby tbirdtbird » Mon Aug 17, 2020 12:51 pm

Which brand pump? name brand or HF? Have you changed the oil in the pump? That can make a lot of difference.
Let's start there; sounds like low charge, but if there are non-condensibles (air) in there that tends to raise the pressures.
How much less or more 134 have you tried? If no recovery machine you don't know how much you removed.
But an evap that is only partially cold tells us that the TXV ran out of liquid 134 to meter in. Low is too low and I would not run it till fixed because you are starving the comp of oil
Last edited by tbirdtbird on Mon Aug 17, 2020 3:39 pm, edited 1 time in total.
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bohica2xo
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Re: 1979 F150 will not cool below 60F register temps

Postby bohica2xo » Mon Aug 17, 2020 3:16 pm

You are undercharged.

Charge 100% of the R12 charge.

The poor vacuum does not help. Not so much moisture, but remaining non-condensable gasses will raise head pressure.

If a 100% charge still leaves the evaporator warm in one place, you may have a defective evaporator.
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jcamp2112
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Re: 1979 F150 will not cool below 60F register temps

Postby jcamp2112 » Mon Aug 17, 2020 3:38 pm

Using a HF vacuum pump. Its kinda old, I'm gonna try a new unit tonight. The 3cfm dual stage pump.

In regards to the charge, i've tried everything really. Started with 12 oz, then 24, oz, then 36, then 48. The spec is for 2.75 lbs, so 4 cans is what the original R12 charge is. I tried 4 cans, and that didn't help either.

I reallly think there are non compressibles in the there due to the vac pump being shot. Because once I did get to 4 cans, the high side was like 250, but low side was still about 15 ish. Any other insight?

I have another evaporator to try in there. Should I just shotgun it and see if that helps?

Also, I have two expansion valves now. The one that came with the kit has a hole in the inlet that I would say is .350" across, where as the new one might have n .080 hole. Does the inlet hole size make a difference really, or does the piston in the txv do all of the heavy lifting? Kinda confused on that too

Here's the two valves side by side:
https://imgur.com/a/Eam1ffG
Dougflas
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Re: 1979 F150 will not cool below 60F register temps

Postby Dougflas » Mon Aug 17, 2020 3:59 pm

Just for giggles, clamp off the heater core to ensure you're not reheating. You may have a partially plugged evaporator.
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jcamp2112
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Re: 1979 F150 will not cool below 60F register temps

Postby jcamp2112 » Mon Aug 17, 2020 5:02 pm

Dougflas wrote:Just for giggles, clamp off the heater core to ensure you're not reheating. You may have a partially plugged evaporator.


Yeah, it's 100% closed off. No extra heat being added. I will triple check one more time to be sure though. I'm also going to flush the evap tonight...

Sucks though, these are all brand new parts, right out of the box. Maybe they pinched a tube when manufacturing, or a glob of solder in there???
tbirdtbird
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Re: 1979 F150 will not cool below 60F register temps/evap partially warm

Postby tbirdtbird » Mon Aug 17, 2020 6:04 pm

Today, unfortunately, new has little meaning.
We had a devil of a time determining why we had high pressures on a system.
Bunch of new parts incl new condenser. Was actually a new install on a vintage car.
Finally decided condenser was no good.
Once it was out, we shook all kinds of shiny aluminum chunks out of it, left in there from mfg.
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jcamp2112
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Re: 1979 F150 will not cool below 60F register temps/evap partially warm

Postby jcamp2112 » Mon Aug 17, 2020 9:05 pm

tbirdtbird wrote:Today, unfortunately, new has little meaning.
We had a devil of a time determining why we had high pressures on a system.
Bunch of new parts incl new condenser. Was actually a new install on a vintage car.
Finally decided condenser was no good.
Once it was out, we shook all kinds of shiny aluminum chunks out of it, left in there from mfg.


Oof, certainly didn't wanna hear that... sure hope that isn't what is happening here. Can't discount it that's for sure
Al9
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Re: 1979 F150 will not cool below 60F register temps

Postby Al9 » Tue Aug 18, 2020 2:08 am

jcamp2112 wrote:Also, I have two expansion valves now. The one that came with the kit has a hole in the inlet that I would say is .350" across, where as the new one might have n .080 hole. Does the inlet hole size make a difference really, or does the piston in the txv do all of the heavy lifting? Kinda confused on that too

Here's the two valves side by side:
https://imgur.com/a/Eam1ffG


What that minor inlet restriction is meant to do - according to patent US5597117 - is to actually reduce NVH by preventing bubbles (that is, refrigerant vapor and any noncondensables) from entering the chamber and collapsing, creating noise.

In my experience, being able to crawl under the dash with the AC on and the blower on minimum speed and listen for any bubbling/hissing noise is a great way to check if there's a refrigerant charge issue other than the obvious constant hiss you get once there's 100% vapor at the TXV's inlet.

Don't know how much it will negatively contribute to the valve's tonnage either.

All in all, having freedom of choice, i'd use one without. As i said before, in my car (a Jap descent Kei car) you have to crawl under the dash to hear TXV noises, if there are any.
Last edited by Al9 on Wed Aug 19, 2020 5:58 am, edited 1 time in total.
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jcamp2112
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Re: 1979 F150 will not cool below 60F register temps

Postby jcamp2112 » Tue Aug 18, 2020 7:45 am

Al9 wrote:
jcamp2112 wrote:Also, I have two expansion valves now. The one that came with the kit has a hole in the inlet that I would say is .350" across, where as the new one might have n .080 hole. Does the inlet hole size make a difference really, or does the piston in the txv do all of the heavy lifting? Kinda confused on that too

Here's the two valves side by side:
https://imgur.com/a/Eam1ffG


What that minor inlet restriction is meant to do - according to patent US5597117 - is to actually reduce NVH by preventing bubbles (that is, refrigerant vapor and any noncondensables) from entering the chamber and collapsing, creating noise.

In my experience, being able to crawl under the dash with the AC on and the blower on minimum speed and listen for any bubbling/hissing noise is a great way to check if there's a refrigerant charge issue other than the obvious costant hiss you get once there's 100% vapor at the TXV's inlet.

Don't know how much it will negatively contribute to the valve's tonnage either.

All in all, having freedom of choice, i'd use one without. As i said before, in my car (a Jap descent Kei car) you have to crawl under the dash to hear TXV noises, if there are any.


Thank you for clearing up that confusion on the valves. Appreciate it. Learning way more than I ever did now about AC, thanks

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