Automotive Air Conditioning Information Forum

Greetings to everyone from a new member.

I am in the process of adding A/C to my 1985 M1009, the military version of a Chevy Blazer. This is my first foray into vehicle A/C after repairing or re-engineering almost everything else on cars.

So far I have installed the blower/evaporator unit, the air box, and the under dash ducting from a civilian Blazer. The vacuum-actuated doors and baffles directing the airflow are working correctly and are sealing tight.

A 16" x 30" parallel flow condenser (biggest I can fit), receiver/drier, and a new evaporator core have been ordered. I will upgrade the engine driven fan, seal the ducting, and add two electric pusher fans in front of the condenser.

My plan for the rest of the system is as follows:

• Install a Sanden SD7H15 on the passenger side. When driven by the original crank pulley, the compressor will idle at 1280 rpm and reach 5760 rpm at engine redline. Is that OK or should I install a smaller crank pulley?

• Fit a TXV to the evaporator core. On the 4 Seasons website I can sort TXVs by tonnage and super heat. What would be good values for the evaporator that originally used a white OT with R12 and the GM pancake compressor?

• Obtain a fitting to connect the suction line to the #12 male O-ring evaporator outlet pipe. That would be a #12 female insert O-ring fitting, which does not seem to exist. Can I use a new accumulator to make the connection to the compressor and if yes, how much oil do I have to add for the accumulator? I could also cut the fittings out of the old accumulator and TIG weld them together.

• Splice in a second aftermarket evaporator unit to cool the rear of the vehicle. This unit has a thermostatic switch that I would like to wire to a solenoid blocking the liquid flow to the rear evaporator? What brand/model of solenoid would you recommend.

• What pressure switches should I install where and what should they control?

If you use a TXV, you need to use a drier and not an accumulator. The locations in the system are totally in different places.

Dougflas wrote:If you use a TXV, you need to use a drier and not an accumulator. The locations in the system are totally in different places.

I know that I need a receiver/drier between condenser outlet and TXV. I ordered a receiver/drier with the condenser and will install it somewhere near it.

However, the original GM evaporator has a #12 male O-ring fitting that I could not find a matching hose fitting for. The evaporator outlet is designed to connect to the GM accumulator and the exit side of the accumulator will accept a #12 female O-ring hose fitting. So, I was thinking to use the accumulator simply as an adapter and insulate it with neoprene foam. It's a hack, I know.

In the meantime I have found the AGS Splice-Lok fittings that I could use for connecting the 3/4" OD evaporator outlet line (after cutting off the fitting) to a #10 hose fitting. I would fabricate a bracket to support the joint so that the hose to the compressor does not stress the evaporator line.

Which approach would you prefer?

Found answers to some of my previous questions.

• It looks like 4 Seasons #38911 would be a candidate for a solenoid valve to control the liquid flow to the rear evaporator TXV.

• Also figured out the electrical wiring. 12V for compressor clutch from dash panel via trinary switch on receiver to clutch. Trinary switch will open clutch circuit when pressure too low or too high. The fan wire from trinary switch goes to a relay coil. Other pole of coil is on 12V (fused). Contact of relay powers electric fan on condenser. Possibly another temperature switch on condenser or radiator to activate relay and fan. Anything more I should add?

Still looking for a suitable TXV to match the old-school GM evaporator. Is 1.5 ton going to work? How much superheat is needed to avoid getting liquid into the compressor? The hose from the evaporator to the compressor inlet is about 2 feet long.

Use the TXV for the 1972 GM line - C20 / Suburban / Impala etc all used the same valve.

Go ahead and use the accumulator along with a Receiver in the liquid line. I do this on TXV conversions, you get a second dryer. Add 1.5 to 2.0 ounces of oil for the added dessicant & the puddle in the bottom of the accumulator. The accumulator gives you a place for the cycling switch & a gauge port.

Use a Receiver / dryer from the 1972 era GM car as well. A large one does not hurt anything.

Some early K5's actually had rear A/C. The rear evaporator is just in parallel with the front circuit. All of the Suburban rear A/C is plumbed that way too. No solenoid valve is needed, because when you shut down the rear fan, the TXV closes almost all the way. Any refrigerant that passes helps keep the return loop moving oil.

Superheat is wildly variable in MVAC. From idle to max rpm, 0 to 80 mph across the condenser, 55f to 125f ambient, and variable flow across the evaporator. We tend to ignore it here.

Your compressor drive ratio should be fine.

bohica2xo wrote:Use the TXV for the 1972 GM line - C20 / Suburban / Impala etc all used the same valve.

Go ahead and use the accumulator along with a Receiver in the liquid line. I do this on TXV conversions, you get a second dryer. Add 1.5 to 2.0 ounces of oil for the added dessicant & the puddle in the bottom of the accumulator. The accumulator gives you a place for the cycling switch & a gauge port.

Use a Receiver / dryer from the 1972 era GM car as well. A large one does not hurt anything.

Some early K5's actually had rear A/C. The rear evaporator is just in parallel with the front circuit. All of the Suburban rear A/C is plumbed that way too. No solenoid valve is needed, because when you shut down the rear fan, the TXV closes almost all the way. Any refrigerant that passes helps keep the return loop moving oil.

Superheat is wildly variable in MVAC. From idle to max rpm, 0 to 80 mph across the condenser, 55f to 125f ambient, and variable flow across the evaporator. We tend to ignore it here.

Your compressor drive ratio should be fine.

Thanks for the very helpful info and suggestions.

I looked up the TXV for the 1972 model year and it is externally compensated but the newer evaporator core does not have the equalization fitting, since it was used with an OT. Should I use a comparable internally compensated TXV (like the 4s 38720) or somehow adapt the switch port of the accumulator to fit the compensation line?

So far, I have not found anyone locally to swage the fittings. Is it OK to use the Aeroquip/Eaton EZ-Clip system? How reliable are they compared to swaged fittings?

Use a similar sized valve - forgot about the external equalization.

Unless you live in some remote spot, there is an industrial hose shop somewhere nearby.

The Aeroquip stuff works well, but you need to use the whole system - hose, fittings & tool Some odd MVAC fittings are not available from Aeroquip. It is used in some trucking applications, and holds up well in class 8 trucks.

The bench tool for standard A/C fittings is available from the site sponsor:
https://www.ackits.com/71550-hydra-krim ... ch=crimper

But it does cost a bit more. If you do a couple of engine swaps a year it really pays for itself.

bohica2xo wrote:Use a similar sized valve - forgot about the external equalization.

Unless you live in some remote spot, there is an industrial hose shop somewhere nearby.

The Aeroquip stuff works well, but you need to use the whole system - hose, fittings & tool Some odd MVAC fittings are not available from Aeroquip. It is used in some trucking applications, and holds up well in class 8 trucks.

The bench tool for standard A/C fittings is available from the site sponsor:
https://www.ackits.com/71550-hydra-krim ... ch=crimper

But it does cost a bit more. If you do a couple of engine swaps a year it really pays for itself.

Thanks again for the advice.

I was looking for old-school A/C shops that do not seem to exist anymore. However, I found two hydraulic hose shops that have the correct dies for the A/C fittings.

To save myself the running back and forth, I decided to buy the swage tool. The swage fittings are more prevalent and less expensive than the Aeroquip/Eaton fittings.

Purchasing the tool will make the Blazer A/C installation more expensive but I already have another project in mind. A variable displacement compressor, driven by a brushless DC motor to cool the sleeping area of my RV with energy from the battery bank when boondocking. About 3000 BTU/hr from ~50OW electric. A small window airconditioner running on the inverter would do the same but the DIY split system will be easier to install inconspicuously and also quieter. Compressor and condenser will be in the belly of the RV and I will adjust the compressor displacement with a microcontroller (my line of work) so that there is no ON-OFF cycling.

Any positive displacement pump is variable output by changing the RPM

The electrically commutated PMDC motors are fairly efficient over a broad speed range. So there is no need to use a variable displacement compressor with a variable speed motor.

A little Sanden with a direct drive (no belt losses) with a displacement that matches your needs would do it:

http://www.sanden.com/productlibrary/ma ... _Rev_2.pdf

bohica2xo wrote:Any positive displacement pump is variable output by changing the RPM

The electrically commutated PMDC motors are fairly efficient over a broad speed range. So there is no need to use a variable displacement compressor with a variable speed motor.

A little Sanden with a direct drive (no belt losses) with a displacement that matches your needs would do it:

http://www.sanden.com/productlibrary/ma ... _Rev_2.pdf

I had looked at the Sanden data sheets and the smallest compressor would have to turn less than 1000 rpm for the desired cooling capacity of 3000 BTU/hr or 880 Watt. That is too slow for the smaller brushless motors. Rather than dealing with a belt or gear reduction, I thought about going with variable displacement compressor. Spinning that compressor in direct drive at ~4000 rpm and adjusting the displacement as needed. The PWM controller for the solenoid valve controlling the swash plate angle is no big deal but the valve is an additional failure point that would require evacuation of the system. Cost for the compressors is about the same.