71 Chevrolet C/10-Pressures good / air only cool?

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phillipm
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71 Chevrolet C/10-Pressures good / air only cool?

Postby phillipm » Wed May 04, 2016 2:43 pm

So I've rebuilt almost all of the A/C system on my truck. New compressor, new lines, new drier. I'm also using a POA and TXV valve from a friend that had it working in his truck. At 80 degrees outside my pressures were 29 and 160 respectively @ 1500RPM with a fan in front of the condenser. Temp at my vents is about 49 at best. That's running down the road. Tube before and after the POA both feel the same cold temperature. Is there anything else that I should be checking? A bit of a noob here but very capable with some direction. Thanks!

Here are some pictures of the system..

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Thanks,

Phillip
Phoenix, AZ
Dougflas
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Dougflas » Thu May 05, 2016 5:23 am

Are you using R 12? Sight glass clear? Disconnect the blower motor and the low side should be at 28 PSi. I used to be happy if those older systems were at 48*. You can check the TXV by removing the sensing bulb, holding the bulb in your hand for a minute or two, see if the readings change. Then place the bulb in a cup if crushed ice and water. The pressures should change again. What is the temp of the refrigerant lines? make sure your condenser is clean and not plugged (on the outside) with bugs. Clamp off the heater hoses or disconnect the heater. On an old vehicle, the seals around the evap could be suspect allowing air to go around the evap instead of thru it.
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Cusser
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Cusser » Thu May 05, 2016 6:24 am

phillipm wrote: At 80 degrees outside my pressures were 29 and 160 respectively @ 1500RPM with a fan in front of the condenser. Temp at my vents is about 49 at best. That's running down the road. Tube before and after the POA both feel the same cold temperature. Is there anything else that I should be checking? A bit of a noob here but very capable with some direction. Thanks!
Phillip
Phoenix, AZ


Phillip - I'm also in Phoenix and it was 100F here yesterday, not 80F !!!

Anyway, your schrader cap in your photo is an R-12 one, so I'll assume that you filled with R-12. But "filled" is a relative term. Let me assume that the system was evacuated (vacuumed) properly before refrigerant was added. 160 psi high side pressure is quite low at 1500 rpm, even if you did measure when only 80F outside; typical high side pressures are in the 250 psi range. So I think you're low on refrigerant.

Did you add cans or carefully by weight using a sophisticated machine?
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phillipm
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby phillipm » Thu May 05, 2016 8:52 am

Dougflas wrote:Are you using R 12? Sight glass clear? Disconnect the blower motor and the low side should be at 28 PSi. I used to be happy if those older systems were at 48*. You can check the TXV by removing the sensing bulb, holding the bulb in your hand for a minute or two, see if the readings change. Then place the bulb in a cup if crushed ice and water. The pressures should change again. What is the temp of the refrigerant lines? make sure your condenser is clean and not plugged (on the outside) with bugs. Clamp off the heater hoses or disconnect the heater. On an old vehicle, the seals around the evap could be suspect allowing air to go around the evap instead of thru it.



Yes I'm using R12, and the sight glass is clear. Some things I know are good, the heater control valve is good, I can hold the lines and feel that they are not letting water through. Also, the condenser is good and clean. I hadn't thought about the seals inside the evap letting air around it instead of forcing air through it. Are there any pics of what one of these units looks like inside so I could visualize it? As for getting the temp of the lines, do you guys just use a laser temp gun or what?

Also, I guess I would be happy is it were 110 out and I was getting 48*, but at 80* I was hoping for better.

Thanks!
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phillipm
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby phillipm » Thu May 05, 2016 9:00 am

Cusser wrote:
phillipm wrote: At 80 degrees outside my pressures were 29 and 160 respectively @ 1500RPM with a fan in front of the condenser. Temp at my vents is about 49 at best. That's running down the road. Tube before and after the POA both feel the same cold temperature. Is there anything else that I should be checking? A bit of a noob here but very capable with some direction. Thanks!
Phillip
Phoenix, AZ


Phillip - I'm also in Phoenix and it was 100F here yesterday, not 80F !!!

Anyway, your schrader cap in your photo is an R-12 one, so I'll assume that you filled with R-12. But "filled" is a relative term. Let me assume that the system was evacuated (vacuumed) properly before refrigerant was added. 160 psi high side pressure is quite low at 1500 rpm, even if you did measure when only 80F outside; typical high side pressures are in the 250 psi range. So I think you're low on refrigerant.

Did you add cans or carefully by weight using a sophisticated machine?



Sorry, yes, I did the gauge readings about a month ago and have been farting around with other stuff. However now that it's 100* out I'm really starting to get back on this again!. I am running R-12 as you suspected. I had it professionally filled after I vacuumed it down to 29" for a couple hours. They used a scale and some R-12 cans that I have in from my stash.

As for the High Side pressures I was going off an AC book from the 70's, and have seen pressure charts all over the place. So, if my High side pressures are a little low are you thinking I'm not condensing it all back to a liquid? Also, what types of things should I look for with a low high side? If there is a good link to another thread I could go there?

Thanks everyone,
Phillip
Dougflas
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Dougflas » Thu May 05, 2016 11:14 am

If you were low on refrigerant, you'd see flashing (bubbles) in the sight glass. To measure the line temps, use of a gun type thermometer is not accurate. The tubing has a reflectivity that will throw the temps off. I use a clamp on type thermometer (you can use a K-type that converts to a voltage on newer digital meters). I you have a gun type and the condenser is dark colored, you can "shoot" the condenser to see the temp changes. At 95 * what is the vent temp at 1500 rpm, doors closed,Max cooling high speed blower speed, fan in front of the vehicle blowing into condenser, and vehicle in the shade?
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phillipm
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby phillipm » Fri May 06, 2016 10:25 am

Okay thanks for the tips. I will try to get the new readings this weekend. I'm also not sure the heater control valve was shutting off all the way. I was under there after driving home from work, left it running as I got out and grabbed the heater hoses and noticed that they were fairly hot. Not as hot as the feed side but still, you wouldn't want to hang on too long. So I zip tied the valve completely closed. If they are still hot after this I may have a faulty heater valve? Or maybe these are designed to let some through? You can see the style I'm running in the pics.
Dougflas
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Dougflas » Fri May 06, 2016 10:47 am

Also make sure the drier is connected in the correct flow position.
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Mr Bill
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Mr Bill » Fri May 06, 2016 8:38 pm

Is it me, or does that condenser look either beat up or dirty?
“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-
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Cusser
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Re: 71 Chevrolet C/10-Pressures good / air only cool?

Postby Cusser » Sat May 07, 2016 8:40 am

Condenser doesn't look so clean to me either. Also make sure the fan clutch is good.

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