Air Conditioning Temps

[ProjectSleeper]

Rather than hi-jacking the Radiator/condensor thread more, I thought it would be best posting this and asking on here..

I just had my Air con system regassed and checked over (had a small leak from the custom pipework previously made up) anyway, me being the nosey bastard I am, I asked heaps of questions and learnt a fair bit about these systems and what makes them work best etc..

Anyway, while testing my system when it was done, we recorded temps of -3.1 degrees from the centre vents. YES, NEGATIVE 3.1 degrees.. The auto electriction was impressed, saying that anything under about 4.0 degrees is considered very good..

so.. my question is - has anyone else checked what their temps are from the vents ??
for Comparison, The way mine was done was as follows..

Sitting and idling for about 5-6 minutes, Fan on Full, Temp on lowest, set to recirculate, doors closed,

another thing I discovered (and this is what related to the other thread), the front "condensor fan" (no name brand 10") is set up as a "push thru" arrangement (ie, sits in front of the radiator and condensor) and it was having troubles keeping the condensor temps down (and as a result, it kept tripping the cut out as the pressure got too high) - although when my Twin 14" Davies Craig Thermos came on, the pressure dropped dramatically and it was coping fine whilst sitting and idling, and holding at a good level..

So, my second question is. What should I do regarding this ??

1. Put a bigger fan in the front
(may be able to fit a 12", but it's still a Push through setup, so it will never be as efficient)
2. Toggle switch to manually turn on the fans when sitting in traffic with the Air con on ?
3. Wire up the thermos to always come on when the air con is on (as well as when the engine temps require it)

comments/suggestions ???

[Mos]

Hey Southo,

Mine got down to 4 degrees in the centre vent but that was with everything open with fresh air - no doubt with recirc and doors closed it would've gone lower. Keep in mind -3 will freeze water, so your evaporator will freeze up if it's getting that low....

The front condenser fan (together with the tiny 6" fan) in the MX83 is designed to only come on when the pressures in the A/C have gone up above normal levels (but not critical). These fans "help" the clutch fan in drawing air through both the radiator and condensor.
By no stretch of the imagination are these to be construed as the *ONLY* fans for the condensor - they are a failsafe - a fully operational clutch fan suffices for both the radiator and condensor, with the 10" generally never being activated.

Regarding your second question, the answer is absolutely
Remove the 10" fan (it does nothing useful) and run the 14s when A/C is activated. This will draw air through the entire surface of the condensor.

Toyota sets it up so the two fans run in series when the A/C is activated (low speed) and then they kick over to parallel operation (high speed) when either the refrigerant pressure goes up or the coolant temp goes up. (This has been covered in another thread before ).
I set it up like that in the AE86 but it's a lot easier just to make them come on with the A/C...

Mos.

[thechuckster]

option 3 would be sensible if the car is used in commuter (stop-start) traffic - but if you mostly use it on the highway, you're rarely going to run into the situation where the condensor gets too hot.

maybe setup one of the 14" fans to come on when the air-con wants to run it's own (useless) fan?

[Mos]

maybe setup one of the 14" fans to come on when the air-con wants to run it's own (useless) fan?

You would be better off turning both 14s on when the pressure goes up.
Personally this isn't ideal, because you're only cooling once a problem arises - kind of like not turning the fans on until the engine start overheating.

Ideally you would want the cooling to happen while it needs it, not after it overheats.

I take your point about unecessary use of fans, so maybe a speed activated switch cuts the fans out at 30km/h or so. That way you still get the full efficiency of the A/C at low speeds and not wasting fans at higher speeds.

Thoughts?

Mos.

[river]

Hi,

Mine was checked last summer at 3 degrees. But, coinsidering it's a 33yo a/c system and doesn't have a fan on the coil I think this is pretty good. Oh, and that's with the new gas, 'cos I'm sure it would of had the old type of gas back in the 70s when it was made.

On a stinking hot day like today, with the a/c going, not only is the inside icy cool, but the engine never goes above 85 deg.

seeyuzz
river

[ProjectSleeper]

Thanks for the replies...
I did a bit of testing today...( couldn't have picked a bloody hotter day if I tried )

I had the Temp probe in the vent all day today and it got down to -7.4 degrees (faark)
(fan on high, recirculate, temp set to lowest, all doors / windows closed and travelling at about 70km/h)
with it turned to fresh, it goes to "only" -3.5 degrees..

I understand what you are saying about the freezing etc, so I will be just setting it to the lowest setting to initially cool the car, then turn the climate control to 20 degrees, as it hovers around zero on recirc and about 2.5 degrees on fresh.. (still plenty cold)

As for the fans, yep, I will wire them to come on with the air con - they are pretty quiet, so it doesnt worry me that they will be on all the time with air con.. (still jeaps quieter than the hydro fan)

Also, when we still had it connected to the regas machine, the pressure that the front fan comes on at is 1500psi (normal is about 1100 - 1200psi) and it on it's own only slowed the rise, not brought it down.. - when the twins come on, the pressure dropped straight away back to about 1250psi at idle in 33 degree ambient temps - with airflow it dropped to about 1100psi so it seems to be coping fine so far...

The air con cut out is at about 3200psi and it doesn't come back on until it drops to 1200psi


IT does appear happy to sit around -5.0 degrees though without any loss of quailty or air flow... but I don't want to tempt fate

[PlacentaJuan]

i did a bit of asking about this because i knew there would be no room for the a/c pusher fan with the intercooler, the guy i spoke to in adelaide (who sounds really good he has done a lot of air con install on modified and re-engines cars and vans) who is going to re-connect my air con said that i would definately need to connect the thermo fans to come on with the air-con

my fans are wired on permantly (will get this fixed eventually) and they are louder than the exhaust!

au thermo fans are pretty strong lol

[thechuckster]

you really want to be measuring the air coming directly out of the core of the internal unit - if you've got -7 at the centre vent, then the air coming out of the core will probably be closer to -10 and rapidly building up ic, lowering the efficiency of the unit to chill air.

It might take longer to cool a hot car down, but you want that central core at just above freezing so any vapour caught on the fins will drain away quickly,