[nUcLeArEnVoY]

Car in question is a 1979 T/A with stock AC, which would be a CCOT (Orifice Tube) cycling system.

When I first bought my car from the PO, he had the AC system serviced which included replacing the compressor with a reman factory-style A6 compressor. I remember everything working fine, but I also didn't understand nearly as much about the car and its systems as much as I do now. I also didn't pay as much attention to the engine temp, and the sender it had in it at the time could have been reading inaccurately.

Then one day not too long after I bought the car, the blower motor stopped working, and I noticed the compressor started to quick cycle on and off. This was back in 2020. It would switch on and run for around 12-15 seconds, then off for a similar span of time, over and over again. Didn't think much of it since the blower motor didn't work, anymore, anyway (which in hindsight might be why the AC was rapid cycling - no heat load since the blower motor was not operating and exchanging air). Either way, it wasn't a big priority and I just enjoyed the car without AC since then.

Anyway, fast forward to today, and due to opportunities afforded to me in the process of making other small repairs, I've since installed a new AC wiring harness, new blower motor, and even resealed all the ducting and verified the blend and mode doors work correctly. I have acceptable blower air CFM coming out all the vents, and the AC does work in that the air is cold. Not freezing, but pretty cold - I mostly attribute that to it being converted to R134a.

Problem is, the engine temp climbs seemingly nonstop once it's running, at least if I'm idling. I finally tested it in 80 degree ambient temps with high humidity here in SoFlo just last night to see how high it would go. I don't think this is a cooling system insufficiency. My cooling system is pretty much completely overhauled: new CC radiator; new Flowkooler water pump with plate properly clearanced; new copper/brass heater core since the original sprung a leak; 160 hi-flow thermostat; new radiator and heater hoses; factory 7-blade 19.5" fan for AC cars perfectly 1/2-in-1/2-out of factory shroud; heavy duty 2747 fan clutch; shroud sealed to radiator using weatherstripping; and factory overdriven AC waterpump pulley. My initial timing without vacuum advance is 18 BTDC as per factory spec. With the AC off, my car very rarely ever passes thermostat temp unless I get on the highway at sustained higher RPMs, but even then not by much. It actually has trouble warming up, the needle usually settles just before the first "tick" on the temp gauge (which I interpret as around 160). I can drive in traffic for an hour and grip my hand around the upper radiator hose and not even get burnt or injured. So again, I don't think this is a cooling system insufficiency, or else it would have made its presence known by now in SOME other way.

So anyway, I closed the windows and doors, set the AC on max with the coldest air and just let it idle to see how high the temp would climb. Two things: the compressor continuously ran without ever cycling off, and two, the engine temp climbed and climbed. I have a factory AC idle solenoid installed and so when the compressor is engaged, the solenoid bumps up the idle to match my standard idle with the AC off (around 750-775 RPMs) so it's not because of a bogged down motor. I got paranoid and turned the AC off once I saw the needle get halfway between the first tick and the 220 tick on the gauge, which I NEVER see it get to with the AC off. The engine bay was noticeably hotter than it usually is, so there was definitely an actual raise in temp. The moment I turned the AC off and gave her some RPMs, the temp dropped immediately and before long, it cooled down to the first tick even at idle RPM.

Yes, I know, the AC will normally raise your engine temp due to the heat coming off the condensor, but come on, that much? The temp didn't seem to show any sign of stopping. The cabin was nice and cool from the AC working, but it's not worth potentially overheating my car. Shouldn't the compressor eventually cycle off? It also makes a pretty noticeable groaning/clicking sound, and was getting pretty hot to the touch. The clutch turns by hand, but with a lot of effort. Maybe I'm naive by how much an AC system will actually raise the engine temp, but I wasn't willing to find out, because if the gauge has even the slightest degree of accuracy, then my little test demonstrated a rise of around 20-30 degrees in engine temp with the AC running. That's not normal.

If my compressor is engaging at all and I'm getting cold air out the vents, then I don't think I have a low freon issue. Maybe my compressor is on its way out and friction is causing it to heat up and strain the engine? Or maybe my pressure switch is bad and not allowing the compressor to shut off, and having the engine continuously run the extra load combined with the condenser heat is causing the temp to climb? High pressure in the compressor sends more heat to the condenser that the radiator has to dissipate, leading to my temp increase, so that would make sense...

I have no idea. I'm just looking for some guidance here. Sorry for the long-winded post. The condenser and I'm assuming the evaporator are the originals; system is converted to r134a. The evap tube and accumulator are cold to the touch while the A/C is on, and they sweat, but they're not frosting over or anything so I don't think there's any restrictions there.

[bhill86]

I’ll be interested to see what you come up with. I have a very similar setup and also similar circumstances in my 77 400 with a few exceptions.

I have a 4 core copper radiator that looked fairly new when I bought the car 13 years ago. I think I have a receipt for it if I remember right. Anyway, new cast impeller water pump clearanced, 7 blade 19.5” fan with the Hayes heavy duty clutch. Everything forward of my evaporator core has been replaced which included a sanden compressor, parallel flow condenser and 134a.

My temp used to creep up as you described until I installed the HD clutch (which you already have obviously) and it really slowed the warming up enough that I haven’t let it sit long enough to see how hot it gets now. It takes long enough that I don’t have any issues in traffic. My initial timing is 14BTDC

I also struggle to warm up much past the 160° t-stat temp if it’s cooler than the high 70s and no AC. I’ve considered going back to a 180° just because I don’t think it’ll effect much with me. Even on the hottest of hot days my max without AC is usually about 180- 187 if I’m on the e-way but it generally gets cooler as soon as I exit and RPMs drop.

My only thoughts for my car are possibly the radiator has a small blockage but I’d think that would effect non-AC temps. My other thought is my condenser has approximately 3/4” gaps on the bottom and part of the sides I planned to seal but haven’t yet. You appear to have both of those things covered though.

[78w72]

I dont have an answer on whats causing the rise in temps... but from what ive read on here & elsewhere over the years, AC will raise temps 20-30°, I dont think that is excessive if thats what yours is doing.

But also remember these cars came with 195 T stats, that would run at about the same as you mentioned on the gauge with the AC off, between the first line & the middle one that says 220, with the AC on stock Tstats would easily let the engine run at 200-210+. So I think you are well within the range of how these cars with AC were designed to run.

Lots of threads on here about guys thinking their car is overheating because it hits 190 or 200, that temp wont cause any engine damage & is not cause for alarm if you hit that on a hot day in florida weather.... now the cars running in 75f temps that get to ~200 with no AC on or while cruising along there may be some things to address for better temps but still not causing any damage.

Hope you can get the temp to where youre more happy with it, but where its at now is not an issue, thats where these cars ran on hot days with the AC on.

[nUcLeArEnVoY]

Originally Posted by bhill86

I’ll be interested to see what you come up with. I have a very similar setup and also similar circumstances in my 77 400 with a few exceptions.

I have a 4 core copper radiator that looked fairly new when I bought the car 13 years ago. I think I have a receipt for it if I remember right. Anyway, new cast impeller water pump clearanced, 7 blade 19.5” fan with the Hayes heavy duty clutch. Everything forward of my evaporator core has been replaced which included a sanden compressor, parallel flow condenser and 134a.

My temp used to creep up as you described until I installed the HD clutch (which you already have obviously) and it really slowed the warming up enough that I haven’t let it sit long enough to see how hot it gets now. It takes long enough that I don’t have any issues in traffic. My initial timing is 14BTDC

I also struggle to warm up much past the 160° t-stat temp if it’s cooler than the high 70s and no AC. I’ve considered going back to a 180° just because I don’t think it’ll effect much with me. Even on the hottest of hot days my max without AC is usually about 180- 187 if I’m on the e-way but it generally gets cooler as soon as I exit and RPMs drop.

My only thoughts for my car are possibly the radiator has a small blockage but I’d think that would effect non-AC temps. My other thought is my condenser has approximately 3/4” gaps on the bottom and part of the sides I planned to seal but haven’t yet. You appear to have both of those things covered though.

You do have newer and more efficient AC system components, whereas I still use a factory style cast iron A6 compressor and coil & fin condenser. Maybe that plays a role with your performance?

Ah, and I only have the gap between the fan shroud and the radiator sealed with weather strip, not the gap around the condenser. That gap remains as it was stock.

Maybe 78W72 is right, I'm just being paranoid. Although, I am curious as to why the AC won't cycle off eventually. It got pretty cool in the cabin after about 5-10 minutes, and this is a cycling type orifice tube system...

[bhill86]

Although, as you pointed out, I do have some modern components mine rarely cycles at idle unless it’s fairly cool outside like in the lower 70s maybe. It’s more so while cruising that it will cycle more but with high ambient temps it doesn’t even cycle a lot

[Goatracer1]

First of all have someone who knows what they’re doing put a set of gauges on your AC and find out if it’s actually working correctly. On a hot, humid Florida day the high side pressure could be 230 psig and that would put a strain on your engine. Remember your engine is not overheating at 220 degrees. Some of the new cars that I worked on had 205 degree thermostats. You may not like the temperature but that doesn’t mean it’s wrong.

[nUcLeArEnVoY]

Originally Posted by Goatracer1

First of all have someone who knows what they’re doing put a set of gauges on your AC and find out if it’s actually working correctly. On a hot, humid Florida day the high side pressure could be 230 psig and that would put a strain on your engine. Remember your engine is not overheating at 220 degrees. Some of the new cars that I worked on had 205 degree thermostats. You may not like the temperature but that doesn’t mean it’s wrong.

Perhaps it is just paranoia, and yeah the AC system itself hasn't been touched in my car since I bought it in 2020, so I don't think hooking up a set of manifold gauges to it to see what's actually going on would hurt after all this time...