1966 Mustang A/C not cooling very well

[IHaveAMustang]

A 50 degree drop from ambient to vent temps is well within an acceptable range. While it's not the best to have mineral oil (what r12 used) and ester or pag oil mixed, the system will usually work. There were \ are plenty of conversions running around that with have or had mixed oils. The oil charge will affect cooling abilities when there is an over abundance of oil, also the original a\c hoses weren't compatible with r134a. They will work with it, but will allow the refrigerant to slowly seep through the pores of the rubber. If you're still running any of the factory lines or if you are uncertain, have new hoses made.

I am running one original hose from the Condenser/Dryer to internal unit.

I guess I need to replace that. I did replace high side / low side hoses when I bought the new R134 kit. Didn't know it would leak out. That makes sense then.

[garycrist]

What are the PRESSURES? Yes old ford systems had an expansion valve. The low side should run 28-30ish for about a 40F reading out the center register on high with recirculate.
So give us the pressures!

BTW the high side about 150-200 with this heat(ambient) we are trying to tame....
If it runs higher, run some water on the condenser to drop the high down...

[Captain Crawfish]

Adding refrigerant is a good way to blow seals out I've done it before . It needs the manufacturers spec and that's it. The psi on each side is a good way to determine if the system is working properly. Definitely get the readings along with the outside temp and compare them to a 134 chart.

[shumpertdavid]

What are the PRESSURES? Yes old ford systems had an expansion valve. The low side should run 28-30ish for about a 40F reading out the center register on high with recirculate.
So give us the pressures!

BTW the high side about 150-200 with this heat(ambient) we are trying to tame....
If it runs higher, run some water on the condenser to drop the high down...

High Side could be as much as 300-325 with Heat index being well over 100.

[IHaveAMustang]

So it looks like my compressor is on its way out.

Low Side pressure was at 60...big problem
High side pressure was at 40...big problem

So I am going to take it to a classic air shop, have them evacuate and purge, replace the drier and compressor and recharge with the correct amount.

Im done working on this myself.

[Captain Crawfish]

I only had to pop one compressor before I got it figured out! Very important not to overcharge. Get a new compressor and do it again. You did all that work might as well learn how to fix it yourself

[shumpertdavid]

Your pressures don't make sense. You can't have a high side reading of 40 and low side of 60. At most they would be equal, but he high side should always be higher than the low side.

[IHaveAMustang]

Your pressures don't make sense. You can't have a high side reading of 40 and low side of 60. At most they would be equal, but he high side should always be higher than the low side.

When revving the engine the low side drops to 40, but at idle it's reading 60.

Brand new R134 gauges.

[shumpertdavid]

When revving the engine the low side drops to 40, but at idle it's reading 60.

Brand new R134 gauges.

ah, ok, I misunderstood.

[LaserSVT]

You can if you have a low charge, too much oil, clogged expansion valve and a hurt compressor. Problem is once the compressor is hurt the drier and expansion valve get contaminated and need to be replaced as well.