Hey all,
I have an 1976 F100 Custom with the factory 360 and factory air conditioning. It has 71,000 miles on it. Several years ago it was converted to R134. Long story short, I got everything back to operating condition. I have replaced drier, the compressor was good along with all the hosed. We put 3.5 lbs of R134. The high pressure was at 220. No leaks but the problem is the temperature is only getting down to 74 degrees. It will not get any colder. So, the question, Any ideas on what to check or what would be causing the temperature to not get any colder. Keep in mind that I have all the tools and equipment to service A/C both R12 and R134. I am not expert by any means, hence me asking what could cause this. I do understand that I will probably have to deservice the system to change something. I just need to know what that something is or is there some other component that can be tested, etc.? I appreciate any opinions and help I can get. Thanks.

 

What's the ambient temp when you read the 74 degrees out of the vent?

Is there good airflow coming out of the vents?

Is the AC compressor clutch engaging?

Have you been able to confirm no leaks in the system?

Do you have an IR temp gun where you can take readings of the hoses at different locations throughout the system?

 

And did you put the right oil in the system?

(Probably ambient temp though)

 

 

He means 3.5 psi, no?

 

 

I'm not an expert either and I've never put refrigerant into my 73 with factory AC (that's a future project), but I'd just put it in til the gauge reads about 3.5 psi. I'd suppose how much he actually needs depends on how big the volume of his system is.

 

what was the low-side pressure? is the low-side line cold? have you confirmed your heater valve is shutting off coolant flow through the heater core?

 

Too much refrigerant will cool as poorly as too little.

Convert Auto R12 system to R134a - Ricks Free Auto Repair Advice Ricks Free Auto Repair Advice | Automotive Repair Tips and How-To has a conversion chart down the page. Or, you can bleed out a little at a time until your output air hits its lowest point.

 

The high side was reading 220 on the gauge. I do not remember the low side. The 3.5 pounds came from a thread I found on line from some A/C guy, or so he claimed. The temperature outside was 84 degrees when we put in the R134. The compressor is engaging, there are no leaks, and we used PAG 46, which was recommended. 7 ounces. Going from heat to a/c the flapper opens and closes. The blower motor is blowing at all speeds low to high.

 

https://www.ford-trucks.com/forums/9...-capacity.html

This was the thread that I followed. I confirmed that the F150 factory installed system was the same as the F100 system.

 

I think he's asking you here if you've checked to see if with the air off but the temp moves to cool, is it blowing ambient temp air or heated air..
If it's still hotter than ambient, then you system is still counteracting itself if that makes sense.
My 79 had a vacuum operated valve that was supposed to (or at some point did (rusted...)) shut the flow to the heater core therefore helping the ac system.
Hopefully I got all that correct or close to correct and helped give an idea of something to check out..

 

No expert here either, but I did convert my Corolla to R134A four years ago and it's still working.

What I learned when I was researching how to charge it was that the best way to measure your fill/charge is by volume. However, the machines which do it like that are said to be way expensive. So most of us are stuck measuring our fill by reading high and low pressures - but that isn't all there is to it. Filling according to pressure requires monitoring another variable, which is the ambient outside air temperature. This is because the pressure varies at different ambient temps.

Someone mentioned a chart above, which might be an ambient temperature vs. pressure chart. That's what I used. I bought the (said to be crap) Interdynamics R134A conversion kit, but then I purchased a can tap so that I could use the 'tool rental' manifold-and-gauge set from the McParts store, which indicate actual pressures via PSI. I also 'rented' their electric vacuum pump. The hand-powered and air-powered vacuum pumps won't really get it done - even though they might get you by in a pinch.
Then I just specified my pressures to what the outside temperature was that day.

I think that the variable of temperature is removed when filling according to volume. And if you look at the info tag for an automotive AC system, it will usually specify the refrigerant requirement by volume (pounds or kilograms).

 

3.5 pounds sounds like way too much.

 

What about the expansion valve? Could that be the issue? The blower motor works at all levels, low to high, the heater works, the vent blows ambient, and when I put it to A/C it gets colder but no less than 74 degrees. The system is still holding pressure. The 3.5 pounds is actually 3.5 12oz cans of R134. So roughly 42oz.