Help diagnosing a/c

[cory58]

I've searched and searched here on r3v and with Google, and can't find answers to my a/c questions, so I'm hoping the questions in this thread might help me and others.

My 92 'vert is 134a converted. The a/c has never worked great. It has a very slow leak. I usually put in 1/2 small can at the beginning of the summer and another 1/2 can later in the summer. I know it's leaking from the low side schrader valve, but don't know if there are other leaks.

I know the pressure switch was retrofitted (and I assume the dryer replaced) when it was converted. The compressor is a Seiko Seiki. Not sure what else was replaced.

Since the A/C is completely out on my Touring, I finally bought a set of gauges and thought I'd "cut my teeth" on the 'vert, since I know the system is at least partially working. Here is the info I got today.

Ambient temp: 86

Static Pressure: 110 low and high

Warmed up car. Turned on A/C full cold, with recirc on. Fan on 2. Took readings from center vent.

At Idle
Vent temp: 69
Low side: 40 psi
High side: 110 psi

At 2000 rpm
Vent temp: 65
Low side: 14 psi
High side: 105 psi

As the car revs higher the discharge temp continues to go down. If I drive it for a while, especially on the expressway, it will keep the interior of the car comfortable at the current ambient temp.

So, here are the questions.

1. What should the static pressure be for a correctly charged E30 system? I've read that static psi should equal ambient temp.

2. Based on the dynamic pressures, any thoughts on problems with the system? I've seen lots of E30 threads showing vent temps in the low 40s with converted systems, so there has to be something wrong with mine.

Thanks, Cory

[cory58]

Quick update that might provide some additional insight for answering the questions above. There was a small leak in one of the fittings on the brand new HF gauge set, so I returned them for a new set. The reading below are with the replacement set.

I had been driving the car all morning Saturday before taking the readings, so everything in the engine bay was hot. Yesterday, I took a static reading with everything cold and then just heated the car up to normal temp and took full readings.

Ambient temp: 83

Static Pressure: 85 low and high (cold)
105 low and high (engine warmed up)

At Idle
Vent temp: 64.3
Low side: 35 psi
High side: 115 psi

At 2000 rpm
Vent temp: 59.1
Low side: 8 psi
High side: 173 psi

Thanks, Cory

[jeffnhiscars]

Static should be equal and about the same at ambient when the engine is cold so that's good.

Your pressures seem on the low side but if you are getting a 19degree differential at idle and 24 at 2k with the car not moving, that's not bad. Remember that AC does not make cold air, it removes btus so the goal of getting the vent temps to X degrees is not scientifically valid. Humidity will limit efficiency and obviously a good fan and moving air will help.

[Das Delfin]

There is a dye you can get that reveals leaks etc. It's common for the schrader valves to leak. Replace them with something like this (the smaller ones on the right side of the picture)

Read Jeff's A/C thread. It's nicely detailed and there's lots of info. He put in a new evaporator that works much better than the original one. If your condensor wasn't swapped out, a newer one designed to work with r134a will increase efficiency, as well as the newer r134a expansion valve. Often times "conversions" just involve fitting adapters and maybe a new compressor so you'll want to check it out if you have records. Or if you can make out the part numbers.

[jeffnhiscars]

He is referring to the parallel flow condenser which dissipates heat far much efficiently which is especially important if your conversion still had an r12 designed compressor. Expansion valve is also a good idea.

[cory58]

Thanks for the feedback! Another r3v member sent a PM with the same feedback re: the condenser - he said that made the biggest difference in his E30 and he lives in (hot,humid) Tampa.

Cory