A/C issues - icing up

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losendos
Posts: 57
Joined: Sun Jun 26, 2016 2:01 pm

A/C issues - icing up

Post by losendos » Sat Jul 13, 2019 4:00 pm

When I bought my car, the factory a/c wasn't working, so I had the system checked. There was no refrigerant, so they recharged it and ran the car for a long time to make sure there were no leaks before giving it back to me. Since then, the system will blow nice and cold sometimes, but as I drive the car, it generally blows less and less cool. The last time I used the a/c, after blowing cold initially, it eventually was just blowing ambient temperature air. I stopped and opened the hood, and found that the a/c line that contains the sight glass was completely frosted over. Once the frost melted, the system was working better again ... for a while.

Any ideas of what would cause this?
-Patrick
1966 Town Hardtop
VTCI #12691
Past Bird: 1986 Turbo Coupe

Cliff Rankin
Posts: 177
Joined: Tue Jan 20, 2015 12:24 pm

Re: A/C issues - icing up

Post by Cliff Rankin » Sat Jul 13, 2019 4:48 pm

Basic a/c would say it is low on Freon or the orfice /expansion valve is bad. But I do not have enough experience with the old compressors that have the adjustment on top of that is what you have. Think of it
Like a balloon and pinching it to get that squick noise.

Cliff Rankin
Posts: 177
Joined: Tue Jan 20, 2015 12:24 pm

Re: A/C issues - icing up

Post by Cliff Rankin » Sat Jul 13, 2019 4:51 pm

Cliff Rankin wrote:
Sat Jul 13, 2019 4:48 pm
Basic a/c would say it is low on Freon or the orfice /expansion valve is bad. But I do not have enough experience with the old compressors that have the adjustment on top , if that is what you have. Think of it
Like a balloon and pinching it to get that squick noise.

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losendos
Posts: 57
Joined: Sun Jun 26, 2016 2:01 pm

Re: A/C issues - icing up

Post by losendos » Sat Jul 13, 2019 5:15 pm

Sorry, but I don't understand the balloon analogy. This is the first time I've tried to troubleshoot an a/c system and I'm learning as I go.
-Patrick
1966 Town Hardtop
VTCI #12691
Past Bird: 1986 Turbo Coupe

stubbie
Posts: 441
Joined: Sat Nov 30, 2013 10:23 pm

Re: A/C issues - icing up

Post by stubbie » Sat Jul 13, 2019 9:47 pm

Just did a bit of reading. According to some, low refrigerant or a leak that will introduce moisture into your system causing the moisture to freeze. Moisture can be sucked into your system by vacuum if you have a leak or the system left open for any length of time. Freezing can also be caused by your evaporator being blocked by debris or the lack of airflow over the evaporator.

Peddller
Posts: 225
Joined: Fri Jul 19, 2013 10:26 pm
Location: Bel Air, MD

Re: A/C issues - icing up

Post by Peddller » Sat Jul 13, 2019 10:04 pm

Can you see ice if you look through the outlet to the evaporator (I think) while it is running and starts blowing tepid air. Also the compressor should be cycling of and on as the car get cooler.
Bill Clark
Bel Air, Maryland
1957 F code
2005 50th anniversary
1963 Avanti R2
1956 GMC Suburban Carrier pickup
1966 Corvair Corsa Turbo
Prior Birds
1963 M code SR
1964 Convertable
1965 convertible

jtschug
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Joined: Fri Sep 11, 2015 1:33 pm

Re: A/C issues - icing up

Post by jtschug » Mon Jul 15, 2019 11:27 am

The way this system is designed, I don't think low refrigerant charge would cause the evaporator to freeze. The basic problem is the compressor is staying on too long. The problem could be a broken probe tube off the clutch cycling switch. These are very delicate and easy to break. Another possibility is hacked up wiring that leaves the compressor on all the time.

The first question is: does the compressor clutch cycle on and off?

marknat
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Joined: Tue Mar 08, 2016 4:17 pm

Re: A/C issues - icing up

Post by marknat » Mon Jul 15, 2019 1:43 pm

I agree with jtschug, sounds like the compressor may not be cycling. Just had a similar problem and found the temperature control relay under the dash near the steering column was not working. This is the switch that is attached to the probe in your evaporator. The probe tells the switch the evaporator is at a certain temp and to turn the compressor on or off.
On my 66 there is a vacuum line that runs to the temp control on the center console.

Cliff Rankin
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Re: A/C issues - icing up

Post by Cliff Rankin » Mon Jul 15, 2019 6:18 pm

Ok , if I may ask. Let’s get to basics. Running a 12 system
Converted to 134 ? Are you running the stock compressor?
How much does it hold by 12 specs. and how much is in there by weight / scale. What are
The high and low side readings on the gages with the system running and what is the temperature outside when you do this ? Do you have a low side pressure switch on the car ? Thanks Cliff

jtschug
Posts: 624
Joined: Fri Sep 11, 2015 1:33 pm

Re: A/C issues - icing up

Post by jtschug » Tue Jul 16, 2019 11:22 am

These cars do not have a low side switch unless someone has modified them.

Temperature control of the evap core is done by modifying the clutch cycling set point with a vacuum diaphram. The pressure in the diaphram is altered in A/C modes with the temperature lever. A probe tube from the collapsible dome goes into the evaporator and should cycle off the compressor when the temperature of the evaporator approaches freezing, but clearly something isn't working quite right.

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