Factory A/C operation

[tqwrench]

Just wanted to check my thinking on the factory a/c in this truck. When I move the top lever from full cold towards the right, does that start cycling the compressor more frequently? Is it supposed to do this? My best guess is they decided to control interior temp this way instead of blending air like we see on later models.

I noted some strange pressure readings on the low side while diagnosing an evap freeze up, seems the TXV is stuck in one position. I have a new one and am prepared to do the whole job (compressor/drier/txv/o-rings/evac & charge). I don't want to throw good into bad if I have another problem on top of the TXV.

[fireguywtc]

I believe that the factory system does raise the cycle point when you increase the temp. There is a switch on the top of the AC box where that cable goes to and it seems to adjust the cycle point. Not totally sure though, I never mess with mine like that, just leave it on coldest setting.

If you are getting a freezing evaporator it could either be sticking TXV or the temp sensor isn't working. It should cycle before freezing. I wouldn't worry about replacing the rest of the system if this is your problem, it seems like everything else is working fine. You can try giving the TXV some good love taps to unstick it or replace it. Also may have to replace that temp switch.

May I ask how bad it was freezing up? Mine freezes on the end tubes of the evaporator, but that I have found is normal and shows good operation.

[tqwrench]

It gets pretty bad, it will leave a small lake under the truck near the evaporator drain if I run it a while then stop and either shut it off or leave it on and turn off the compressor. It's also leaking through the bottom of the case, seems the seal is shot. Most of the water goes through the drain hose but some gets on the floor. I thought it was moisture in the system so I evac'd and refilled it, no dice, same deal. I pulled an hour vacuum on it with a 2 stage 4 CFM pump too.

Thanks for the reply. Seems like a TXV should get it working better.

[fireguywtc]

I believe that water is normal from the humidity, especially were you live. I get the same result including a little water in the cab.

[ToughOldFord]

I can't speak specifically to the factory AC, but I've never seen an older system that cycled at all. My 69, for example, the compressor clutch is directly wired to the fan control. As soon as the fan is on, the compressor is on and stays on until the fan switch is turned off. It's a dealer add on AC, but all of the old AC units I've had from the 60's and 70's were wired like this.

Again, I can't specifically speak to the factory system, it is possible Ford was ahead of its time, but I'd be surprised. It's easy enough to check though if there's a pressure switch plumbed in somewhere.

[motzingg]

the 'clardy' customatic dealer add-on unit that i have uses two controls, one is the fan, the second has a thermocouple tube going into the evap coil and controls the cycling of the compressor. It doesn't adjust the compressor cycle arbitrarily, it actually uses the sensed temp of the evap coil to cycle the compressor based on demand.

I'm debating chucking it because i think i'd rather just have 'always on' air rather than risk the compressor getting cycled too frequently and beating up the clutch mechanisim more.

[tqwrench]

ToughOldFord, I hear you. I cut my teeth on the GM CCOT system and later got experience on VIR and POA valves (neither of which ever cycled). This is strange and kind of foreign to me, and I see why it wasn't carried forward. If I leave it in full cold all the time it will freeze the evap pretty good and looking at the shop manual, IT SHOULD! They designed this thing to operate down to 12 PSI, and with R12 in it, you can bet it will make a brick of that evap core. That cycling switch feature does kick in right about the time the iceberg starts forming, even in full cold.

Moving the lever away from full cold allows the compressor to cycle, but it seems to increase humidity in the cab somewhat, since what melts is blown off the evap into the cab.

At any rate, this system and I have come to terms with one another. I've figured it out and can manage to keep it comfortable and not brick my evap core, so I'm OK for now. I can refrigerate the interior if I want to. I left it on full cold mode and drove it to Lowes one day, got out of the cab and my eyeglasses fogged over so bad I went blind, the feeling in my right leg returned after a few aisles too

[motzingg]

haha that's awesome... i have fantasies about that...