This topic may have been covered before, but bear with me if it has, because I couldn't find a good discussion thread in keyword searching.

I have 1) a problem with my air conditioning, and 2) wondering how to keep the engine running cool with the a/c on, even in hot weather. Story below:

PART 1.

My cherry 74 Dart Swinger with 49K miles on it drives great, with the exception being recently, the hot weather out here in SoCal causes some dieseling issues. I'm going to be working on some mods to the gas line and perhaps a heat shield for the carb to aid in keeping the gas and carb cool.

I need some good ideas regarding air conditioning. The stock setup works well, but causes the engine temp to rise considerably. On a hot day, this is totally understandable, esp. since my car is completely factory with no mods at all.

Yesterday, running on the freeway at about 65mph from Burbank (hot), to Chatsworth (Hell Hot, prob. about 95-100 degrees), the temp needle was pointing midway on the temp gauge w/out the a/c running. Respectable enough. I realize driving 65mph is a larger load on the engine than driving, say, 55mph. But driving 55mph in LA traffic is not always a great option, so sometimes, 65mph is the necessary minimum.

As soon as the a/c was turned on, it blew nice and cold, but it caused the temp gauge to creep up to the high end of the 'safe', but HOT range. I played with the a/c temp control going to Hot, and then swinging back to Cold again to try to regulate the temp and keep the compressor from being on all the time. But then, at full 'cold' the a/c stopped blowing cold and became just "warmish". Getting off the freeway, I turned the blower fan down to low, and listened, as I switched the a/c on and off and played further with the temp control. It sounded like the compressor wasn't on; I just heard a 'click' and a 'sssss' sound, though the engine did slow some as though a load was engaged. But I could not get the A/C to blow cold again, as before. I turned it off, not wanting to cause damage to anything and suffered on the drive home.

This morning, turned the A/C back on to test it, and it was blowing cold again, though the engine at 'Drive' idle does 'complain' and...not buck...but kinda struggle a little when the a/c is engaged.

I don't know what's happening. This kind of thing happened once before. Took it to the mechanic who looked, said nothing was wrong, and it was working fine. It wasn't blowing cold when I brought it to them (same story at that time; hot weather, running warm, stopped blowing cold a/c, stopped engaging the compressor clutch), then got it back and it was working ok. What do you think this problem is about?

PART TWO.

So what are some good modifications to make to the factory a/c and cooling system setup in a 74 Swinger so that even on a hot day with the A/C on, the engine will run cool? I see people install pusher fans for additional airflow; some even remove the factory fan and go just with the pusher fan because there's not enough room. I've heard about different thermostats that cause the engine to run cooler. Also, a plugged radiator could cause the temp to run hot. Built up crud in the block, head and water jacket could be creating additional insulation, causing the temp to rise unnecessarily (I wonder how much mine has with it's mileage)?

I need some good ideas of what to do to help stem this problem. Regular weather doesn't pose a problem, but hot weather definitely causes my engine to run differently and more problematically.

Hi, I`m new at this, but are you sure, that your AC, is original?
I`m asking, because I have a sticker, in my enginebay, that says, "NOT BUILD FOR A/C"
And I have a nice little supersix!

If you are running with some aftermarked A/C unit, I would advise you to buy a bigger radiator, and build a shroud, for the fan!

but thats just me,

and, when was the last time, you cleaned the system?

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There`s a sticker on my car that says!

Somwhere in texas, there`s a village
missing it`s idiot!

you know what, it`s the truth! hehe

I'll agree, sounds like a bigger radiator is in order, flush the cooling system, and either shroud the fan, or upgrade to an electric unit...more air through more radiator = a lot more cooling. Also, what temperature of thermostat are you running? Coolant mix? Any additional cooling additives?

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Y'know, my Dart sounds a lot like Anthony Michael Hall's Canadian girlfriend in "The Breakfast Club"...

I don't agree that one follows from the other. These cars cooled OK (not great, but OK) in stock form with the A/C on. There are going to be two categories of things for you to look for and address: Things that need repair and things that need improvement.
This is a very clear indication that you do not have enough effective radiator capacity. It is not an indication that you need more fan capacity, or a better fan shroud, or anything else having to do with airflow. Remember, the fan and shroud are irrelevant when the vehicle's moving forward at any substantial speed, because the vehicle's forward motion pushes plenty of air through the radiator. If you had airflow problems due to insufficient fan or a missing or broken fan shroud, your engine temp would rise unacceptably and your A/C performance would be marginal at idle and very low speeds (stuck in traffic) but the engine and A/C would cool down nicely at higher vehicle speeds. That's not what you describe as the problem, so you've definitely got a coolant-heat issue, not an airflow issue. Remember also that the fan and shroud become obstructions to airflow through the radiator when the car's moving fast enough to push sufficient air through without the fan. This goes double for extra supplementary pusher fans and so forth. They work for you at idle and low speed, and work against you at higher car speeds.

(NB an electric fan with a control circuit set up to provide a few minutes' fan runtime after shutdown would help with your hot-fuel issues, but would also add some other issues to deal with, mostly charging-related.)

Let's review: Your '74, if it has factory A/C, should be equipped with a 22" wide radiator (measured at the actual radiator core, not from outer bracket edge to outer bracket edge), a fan shroud, and a 6- or 7-blade fan. Does this match the configuration of your cooling system?

With extremely low miles and a lot of sitting, it's likely there's a fair amount of crud and corrosion in your radiator and engine block. Remove the radiator cap and drain the coolant down until you can see the tops of the radiator tubes. Take a good look at them. Do you see any fluffy "solder bloom" buildup around the edges? Any chips and chunks clogging the tubes themselves? The deterioration that reduces a radiator's efficacy is not always visible this way, but it's a good bet your radiator could do with a good thorough cleanout at least. Me, I would lean towards the "fix it once and for all" approach and have the rad recored with a 3-row high-efficiency core. Couple hundred bucks at a good radiator shop; I'll bet Hemi Andersen can point you at one. He's in Ventura.

It's also a pretty good possibility that your block might have some crud buildup creating an insulating/blanket effect. The "in car" fix for this involves removing the freeze plugs from the manifold side of the block and physically scraping/digging the crud (piano wire or straightened-out coat hanger) for subsequent flushout with high-pressure water.
That doesn't work on A-bodies made after '73 with factory A/C, which are equipped with EPR valves and run the compressor full time whenever an A/C mode is selected (that is A/C, MAX A/C, or DEF).
If you got the click and hiss, the compressor was indeed on. For future reference, you can check this by opening the hood and looking. If the plate on the front of the A/C compressor clutch is stationary, the compressor's not turning. If the plate is spinning, so is the compressor. Was it a humid day? It's likely your loss of cabin cooling was due to evaporator freeze-up: for one reason or another, the EPR valve didn't do its job correctly, and the evaporator (the heat exchanger inside the car) was overcooled. Ambient humidity condensing on the cold evaporator then froze and the ice crystals grew until they blocked airflow over the evaporator, which reduced cabin cooling. You turned off the A/C, the evaporator was no longer being cooled, the ice melted, and the next time you tried out the system, it was working correctly. Note that is only one of a few possible explanations for loss of A/C performance. Could be a sticking or leaky EPR valve, could also be a sticking expansion valve, a moving obstruction on the air inlet side of the evaporator (leaves, other trash). Could be noncondensibles in the system, or an issue of insufficient condenser capacity at low speeds. What's the history on this A/C system? Still running R12 with all original components, or converted to R134a or something else? If converted, exactly what-all was replaced and serviced as a part of the conversion?

Please define this struggling and bucking you get at idle with the A/C on. Do you get noises from underhood? Remember the A/C compressor does throw a large torque load on an idling engine, so the base idle speed will need to be a little higher than on a non-A/C car — the best setup is an idle kicker solenoid that bumps up the idle a little whenever the compressor's engaged, but those are not always practical to add. You still running the stock Holley 1945 carb?
Are you sure the compressor was disengaged? And when you say the A/C stopped blowing cold, do you mean it started blowing ambient-temperature (warm/hot) air, or did it just blow "less cold"?
See above. You need more effective radiator capacity to solve the engine-heatup problem you're having. I emphasise "effective" because a radiator that might've started out adequate grows less so with corrosion and gunk.
Well, you could install a lower-temperature thermostat (180° rather than the factory 195° item). Thermostat selection is a balancing act. The hotter you can run the engine without problems, the better will be your fuel economy and the less HC and CO your exhaust will contain. But with a carbureted fuel system, as you increase the thermostat temp, you start running into heat-related issues and pinging much sooner than with EFI. In a hot climate like yours, with a car like yours, I think you would probably be best off with a 180° thermostat; preferably a Stant SuperStat #45358.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

yes
I'll get back to you after I've checked. It's a possibility my radiator has been refilled with water, not coolant, in the past. I know there's a slow pinhole leak on the top tank, but it was presented as being an unwarranted repair unless I was ready to do a whole radiator job. Now may be the time to go with your 3-row high-efficiency core suggestion.
I don't doubt it. This car existed at around 29K-35K miles for probably around 20 years or more, being minimally driven.
How effective is this really? (digging with a piano wire or straightened out coat hanger) And easily done by me, a newbie at being an in-house mechanic? Where is the IN for the high-pressure water to be placed (on the block)? Is this something I would do, or take to have be done?


I hadn't had a chance to do this yet, but yesterday I took a look. With the thermostat set to full cold, and observing the compressor, it's clear to me there's some kind of compressor clutch problem. It would engage for two seconds, stop. Engage again, then kinda jerk and stop. Which I know is not normal. The whole thing should have been turning, the entire time the A/C was on. That odd hissing noise I mentioned before was present, but it wasn't normal "compressor" hiss, it was some kind of slipping noise. Smoke rose from the clutch after I disengaged the A/C. It may be time for either a clutch or compressor re-build. This thing hasn't been used with any regularity in probably 25 years.


No, dry as a bone.

That could definitely be if the compressor was engaged the entire time, but from my deduction above, it is probably not the case in this instance.
Still running with R-12. Not switched over.
Thinking about it, other than the normal sound of the engine slowing down because of the large torque load, no. There has been some noticeable idle fluctuation when sitting at a stop, engaged in Drive, when the idle is at its lowest point. That may just be a matter of boosting the idle slightly during hot weather to compensate for the additional load on the engine from the compressor. Perhaps the fluctuation is the compressor engaging and disengaging.
I have not observed this to be the case. In the past, under 'normal' operation, without any of these odd symptoms, when I adjust the temp control slider to a warmer "cool" setting than "full-cold", the compressor will periodically 'click' and disengage via its clutch when the temp inside the cabin reaches that of the temp control.
Honestly, I haven't a clue, but I'll look. Everything is stock, so probably yes.
No, I'm not sure. But it didn't blow "less cold", it blew warm, uncooled air. Felt like it was from outside.

Thanks Dan.

And to the others who posted above, my car is a factory A/C setup, with the 7 blade fan, and shroud, etc.

And yes, there is solder bloom in the radiator tubes after a visual inspection. So clearly, it's time for some maintenance.

Depends on how much sweat you put into it!
Start by removing the rearmost freeze plug (helps to remove the starter). Dig and scrape around, disconnect the lower radiator hose, and force high-pressure water into the block through the rear freeze plug hole. Crud should get flushed forward and ejected from the lower rad hose.
Okay, yep, that's probably a slipping A/C clutch. Normally they last more than 50k miles, but it sounds like yours is having problems. Some electrical testing ought to be done before putting a clutch on it, first, to make sure the clutch isn't OK and just receiving intermittent/weak power due to a faulty wire or switch.
The clutches generally don't deteriorate from age, and you haven't given any indication there's anything wrong with the compressor itself.
Again assuming this is a factory A/C setup, with the two slider levers in the dashboard (one to select A/C, vent, heat, defog, or whatever; lower one to adjust the temp) there's no switch in the system that would make it behave as you describe. Starting in '74, there is no clutch cycling switch as found in '73 and earlier A-body systems. The only two switches in the '74-up system that can control power to the compressor clutch are the mode selector switch (power to the compressor clutch in A/C, MAX A/C, and DEF modes), and the low-pressure cutout (LPCO) switch. If this system is all original, it's possible you've simply got a borderline low refrigerant level; you'd still get some car cooling, but the LPCO would intermittently trip and cut out the compressor. With the compressor engaged and the engine running at a fast idle, take a look at the sight glass on top of the filter-dryer (wipe it clean with a cloth): Do you see bubbles and foam flying past the glass, or is it clear all the way down to the bottom?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Actually, they do...........

The 2 metal pieces wear down and the air gap gets bigger and bigger.

One metal piece is on a rubber donut, and eventually the electromagnet can't consistently move the plate enough to overcome the resistance of the rubber donut and you get weirdness.....

Usually there's some spacer washers on the shaft that you can remove/replace with ones of different thickness to lessen the air gap on the plates to fix the problem.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Yeah...with use. I said they don't deteriorate from age (i.e., sitting around unused or little-used for years and years).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I can't say for sure, but if I remember correctly the "A" bodies, with manual A/C, never used the EPR valve, only the "full sized" cars. I looked up the wiring diagrams, I have, 1964 to 2007 (missing from 71-78) and all the smaller mopar cars from 64 to 70, and 79-89 had a evap temp clutch cylcling switch.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Nope. Clutch-cycling switches on A-bodies through '73, EPR valves from '74-'76.
You're missing the '74-'76 A-body diagrams, then, if you don't have the '71-'78s.

No clutch cycling switch in '74, '75, or '76 on the A-bodies. And there were no A-bodies in the '79-'89 year range; not sure why they're coming up in this discussion. For reference, FPCs up to '73 show part type code 24-24-150 as "SWITCH, Evap Temp Control", applicable only to Dart and Valiant; that PTC is not present in the '74-'76 FPCs. I'm not sure what sort of evap temp control was used in the F- and M-bodies, nor in the OmniRizons, but the K-derivatives had fixed (non-adjustable) clutch cycling switches in conjunction with hot/cold air blending. But I am definitely certain there is no clutch cycling switch on a '74 A-body.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Like I said, I can't say for sure, just going by memory (which is not that good, at my age), since some of my wiring diagrams have gone into hiding. When I look at the vehicle, it jogs the memory. I realize there are no "A" bodies 79-89, I was just stating the wiring diagrams I had available. I referded to these as "smaller" cars. Most of the later year ( in the 80's) manual A/C cars had either a mechanical evap temp switch, or a solid state evap temp switch, in the suction line at the firewall, or a damped presure sensing switch on the suction line, to prevent evap freeze up. Temp control was by hot/cold air blending.

The easiest wat to tell if the vehicle has an EPR is to look at the compressor. Only the large Chrtsler V-2 compressor used the EPR valve. Some did, and some did not. Look at the fitting at the back of the compressor. If there is a service port on the suction fitting, and the cyl head, the compressor has (or should have) an EPR valve, constant run compressor. If there is no service fitting on the suction fitting (only the cyl head fitting) it is a clutch cycling system

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225