1979 Ford F150 A/C not cooling - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 14 (permalink) Old 07-23-2012, 02:05 PM Thread Starter
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1979 Ford F150 A/C not cooling

I have a 1979 Ford F150 1/2 ton P/U XLT, 4WD 6.6L 2BL OHV 8cyl that I'm trying to put A/C back in. The truck had factory air, but the evaporator is the only original part in this setup (along with the controls inside the cab on the dashboard).

The new compressor is working. All the pressures look good (the low side is around 35 to 40). But we're finding that the air out of the vents is only dropping 20 degrees max. We've checked to see if the blend door was not working and it was getting heat from the heater core. We blocked off the heater core completely with the same results. It just doesn't seem to be getting cool enough. The large fittings on the firewall should be cold (maybe 40 degrees), but it's only cooling to about 79 degrees, about a 15 degree drop.

We cannot see into the evaporator box to see if there is an expansion valve in the system, but we did not put an expansion valve in with the new system we put on.

Any advice appreciated!

Thanks,
Lisa
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post #2 of 14 (permalink) Old 07-23-2012, 05:06 PM
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Re: 1979 Ford F150 A/C not cooling

What are your low and high pressures?
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post #3 of 14 (permalink) Old 07-24-2012, 06:55 AM Thread Starter
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Re: 1979 Ford F150 A/C not cooling

the low is around 35-40. The high is around 215.
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post #4 of 14 (permalink) Old 07-24-2012, 08:14 AM
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Re: 1979 Ford F150 A/C not cooling

With R-134 you can run as high as 350 on the high side.

But the 35-40 is almost there for perfect on the low side.

Give it another couple ounces of refrigerant and see if it improves things a bit.
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post #5 of 14 (permalink) Old 07-24-2012, 11:40 AM Thread Starter
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Re: 1979 Ford F150 A/C not cooling

Ok, we tried that. Unfortunately, it's still the same as far as cooling. The high side went to 275. And that is well over what the guy who I purchased the compressor from (Nostalgic Air Parts) said to charge it. Right now, we have about 30 oz. in it and he says to have it at 24 oz.

signed scratching my head,
Lisa
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post #6 of 14 (permalink) Old 07-24-2012, 01:30 PM
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Re: 1979 Ford F150 A/C not cooling

The amount of refrigerant you need is directly related to the cubic feet of system you have.

It's eating me up too, but I've been away from AC systems for 6 years now.
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post #7 of 14 (permalink) Old 07-24-2012, 03:38 PM
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Re: 1979 Ford F150 A/C not cooling

The expansion valve should be back at the firewall inside the engine compartment. I assume you also replaced the drier and at least flushed the condenser out. Otherwise, you may have a partial flow blockage somewhere in the system.

I rebuilt mine and it doesn't get freezing cold either.

1965 289 mustang fastback
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post #8 of 14 (permalink) Old 07-25-2012, 10:03 AM Thread Starter
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Re: 1979 Ford F150 A/C not cooling

We cannot find an expansion valve. Should there be one there?

By the way, all parts are new, except the evaporator and the dials on the inside dashboard which control the A/C.

How do I figure out the cubic feet of the system I have?

Signed still scratching,
Lisa
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post #9 of 14 (permalink) Old 07-25-2012, 07:37 PM Thread Starter
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Re: 1979 Ford F150 A/C not cooling

I know I'm grasping at straws a bit, but does anyone think it could be an electrical/thermostat issue?
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post #10 of 14 (permalink) Old 07-25-2012, 09:53 PM
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Re: 1979 Ford F150 A/C not cooling

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Originally Posted by lisagk View Post
We cannot find an expansion valve. Should there be one there? Lisa
Won't have an expansion valve, it'll have an orifice tube in the inlet tube on the evaporator core. Even my 85 F-250 had an orifice tube - I don't know what year they changed to using an expansion valve.

Best advice I can offer is to pull the system apart and flush the lines, condenser, and evaporator. Replace the drier, orifice tube, and o-rings. Reassemble the system & put in the compatible oil for the refrigerant you're going to use. Pull a vacuum on the system & make sure it holds it. Then recharge with refrigerant and see what it does.

1985 Ford F-250 6.9 Diesel | VIN 1FTHF2518FPB11135 | Stolen in 2007.
1968 Lincoln Continental | VIN 8Y82G804408 | Stolen in 2010.
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post #11 of 14 (permalink) Old 07-27-2012, 10:38 AM
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Re: 1979 Ford F150 A/C not cooling

Mine is a 79 with factory AC and has the expansion valve. LMC Truck part number 43-0762.


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post #12 of 14 (permalink) Old 07-27-2012, 11:42 AM
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Re: 1979 Ford F150 A/C not cooling

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Originally Posted by Hottarod View Post
Mine is a 79 with factory AC and has the expansion valve. LMC Truck part number 43-0762.
Weird, because the 73 truck I redid the A/C on years ago had an orifice tube setup - though it might not have been a factory install. And when I look up my old 85 diesel online it says it should have an expansion valve - yet I know better - it had an orifice tube. I rebuilt the system myself and converted it to 134.

Edit : well, according to LMC the 85 did use an orifice - yet a couple of the parts house sites say different.

1985 Ford F-250 6.9 Diesel | VIN 1FTHF2518FPB11135 | Stolen in 2007.
1968 Lincoln Continental | VIN 8Y82G804408 | Stolen in 2010.
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Last edited by jeremyl; 07-27-2012 at 11:45 AM.
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post #13 of 14 (permalink) Old 08-02-2012, 06:29 AM Thread Starter
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Re: 1979 Ford F150 A/C not cooling

we found an expansion valve and modified the hose for it. It's installed and cooling. But now it's getting TOO cold and freezing up.

one step forward....
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post #14 of 14 (permalink) Old 08-06-2012, 06:38 AM
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Re: 1979 Ford F150 A/C not cooling

Wish mine would get too cold. We had that problem in a work truck and would just turn the ac off from time to time. A thermostatic switch to cycle the compressor on and off would fix this but my truck doesn't have one of those. I suspect yours doesn't either. It may be something you can add.

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