1988 r30 with newer motor ac problems 7.4 liter

[Grit dog]

Post pics. I hate that they swapped in a better EFI engine and then stripped all the benefit out by swapping a carb onto it. I can show you how to properly splice in the AC controls on an L29 motor, but it sounds like they hacked it all up anyways.

Tell me about it, lol. The engine in our 86 was a low mile pull out straight out of a late GMT400. GenVI engine. Sure would have been nice to have the serpentine belt, newer AC and EFI…
I guess the one good part is all the OE controls work easy with a carb including the cruise control.

 

[Grit dog]

Nice! Whoever did yours at least kept the serpentine belt setup.
Fwiw like I posted above I have same engine in basically the same truck. Except mines running all the original style accessories including AC, off of v belts.

 

[Bextreme04]

i sure do appreciated it. i don't mind buying all new components. to make it right i want to daily this dually when i am done. i can pay someone to do it but i think that's what's wring with the world today i want to learn how to do it. the wiring and vacuum hose is what's scaring me now after speaking with you. i don't know where any of the wiring goes to and from the compressor from low pressure switch and from high pressure switch.

I can probably help you out with that. I have the wiring diagrams for everything and have the exact same motor. I'm still trying to find the time to finish the swap on mine, but am very close and pushing to do it this year. You should actually have the stock compressor connection near there already. You'll just have to splice it to the compressor connection. I'll look tonight and see if I can send you the full connection layout including a website I've used to get the replacement GM connectors and pigtails. You should be able to splice in at a single wire on the factory harness and then just wire the ground side through the high pressure cutoff switch and then to a good ground. Pretty basic really and shouldn't cost you more than a few hundred dollars for the replacement components that have been sitting out and are missing.

 

[Bextreme04]

Tell me about it, lol. The engine in our 86 was a low mile pull out straight out of a late GMT400. GenVI engine. Sure would have been nice to have the serpentine belt, newer AC and EFI…
I guess the one good part is all the OE controls work easy with a carb including the cruise control.

The worst part, in my mind, is that his is an 88, so it was already EFI. At least with yours it was already carb. There must be a FPR somewhere and it would be using the stock in-tank pumps... I assume.

 

[Grit dog]

The worst part, in my mind, is that his is an 88, so it was already EFI. At least with yours it was already carb. There must be a FPR somewhere and it would be using the stock in-tank pumps... I assume.

Presumably.

 

[montrosemafia]

I can probably help you out with that. I have the wiring diagrams for everything and have the exact same motor. I'm still trying to find the time to finish the swap on mine, but am very close and pushing to do it this year. You should actually have the stock compressor connection near there already. You'll just have to splice it to the compressor connection. I'll look tonight and see if I can send you the full connection layout including a website I've used to get the replacement GM connectors and pigtails. You should be able to splice in at a single wire on the factory harness and then just wire the ground side through the high pressure cutoff switch and then to a good ground. Pretty basic really and shouldn't cost you more than a few hundred dollars for the replacement components that have been sitting out and are missing.

thank you so much for the help. i will look tonight to see if i can find the connector. there several of them laying everywhere from the TBI swap to carb. i noticed on the dryer for the newer model it doesn't have a low pressure switch connection. or i didn't see one. does it have on in the hose on the newer style HVAC?

 

[Bextreme04]

thank you so much for the help. i will look tonight to see if i can find the connector. there several of them laying everywhere from the TBI swap to carb. i noticed on the dryer for the newer model it doesn't have a low pressure switch connection. or i didn't see one. does it have on in the hose on the newer style HVAC?

The newer style manifold has the low pressure and high pressure switch right there at the compressor. The switches are on the engage signal circuit, but the compressor power itself is a relay. The squarebody uses a single switch in-line with the compressor engage signal. I personally just wired the signal coming out of the squarebody low pressure switch into the high pressure switch on the compressor. This signal then goes into the PCM to provide an "AC Request" signal. The PCM then will send a signal to the AC Relay to engage the compressor as needed. I then wired in a three wire AC pressure sensor from a '99 F-Body to feed the PCM with the information it needs to control the compressor and electric fans.

Your application would be much simpler. I would recommend a relay installed on the firewall. I can draw up a wiring diagram and probably give you a parts list for the connectors, then you would just need to create the harness and plug it in at the appropriate spots. It should be able to be almost completely stand alone without needing to cut into the factory harness at all. Power to the relay would come from the post on the firewall that feeds the power to the AC blower, signal power from the squarebody low pressure switch, signal ground through the high pressure switch to a stud on the engine. Then you just run main power out to the compressor from the relay and then ground to the engine block with a flyback diode to keep it from sticking on or surging back through the vehicle electrical system when the relay disengages.

 

[montrosemafia]

The newer style manifold has the low pressure and high pressure switch right there at the compressor. The switches are on the engage signal circuit, but the compressor power itself is a relay. The squarebody uses a single switch in-line with the compressor engage signal. I personally just wired the signal coming out of the squarebody low pressure switch into the high pressure switch on the compressor. This signal then goes into the PCM to provide an "AC Request" signal. The PCM then will send a signal to the AC Relay to engage the compressor as needed. I then wired in a three wire AC pressure sensor from a '99 F-Body to feed the PCM with the information it needs to control the compressor and electric fans.

Your application would be much simpler. I would recommend a relay installed on the firewall. I can draw up a wiring diagram and probably give you a parts list for the connectors, then you would just need to create the harness and plug it in at the appropriate spots. It should be able to be almost completely stand alone without needing to cut into the factory harness at all. Power to the relay would come from the post on the firewall that feeds the power to the AC blower, signal power from the squarebody low pressure switch, signal ground through the high pressure switch to a stud on the engine. Then you just run main power out to the compressor from the relay and then ground to the engine block with a flyback diode to keep it from sticking on or surging back through the vehicle electrical system when the relay disengages.

ok thank you. i have to work 16 hrs till Wednesday and then i am going to get back on it. i believe i follow what your saying. thanks so much for the help. is the high pressure switch on the ht6 compressor on the back?

 

[Bextreme04]

ok thank you. i have to work 16 hrs till Wednesday and then i am going to get back on it. i believe i follow what your saying. thanks so much for the help. is the high pressure switch on the ht6 compressor on the back?

Yes. That's the high pressure switch. The original low pressure switch is on the manifold right above it that has the hoses cut off in your picture. The squarebody has the low pressure switch on the filter dryer instead, and doesn't use a relay. So the entire compressor engagement amperage is being driven through that switch. The components will last a lot longer if the switches are only turning on/off the low amperage command signal, which is then commanding a relay to engage the compressor clutch.

 

[montrosemafia]

Yes. That's the high pressure switch. The original low pressure switch is on the manifold right above it that has the hoses cut off in your picture. The squarebody has the low pressure switch on the filter dryer instead, and doesn't use a relay. So the entire compressor engagement amperage is being driven through that switch. The components will last a lot longer if the switches are only turning on/off the low amperage command signal, which is then commanding a relay to engage the compressor clutch.

ok i am getting there i believe i am fully understanding everything. you have been a big help i hope install this weekend. i still am not sure where the low and high pressure switch wire into? a relay? then out of relay to compressor clutch?

 

[montrosemafia]

Yes. That's the high pressure switch. The original low pressure switch is on the manifold right above it that has the hoses cut off in your picture. The squarebody has the low pressure switch on the filter dryer instead, and doesn't use a relay. So the entire compressor engagement amperage is being driven through that switch. The components will last a lot longer if the switches are only turning on/off the low amperage command signal, which is then commanding a relay to engage the compressor clutch.

i thought the low pressure switch was on the dryer?

 

[montrosemafia]

ok so... LOL heres where i am. i got new compressor, hoses, dryer and head unit.

i got the fan to blow on all speeds. i jumped the low pressure switch out and it sent voltage to the pig tail for compressor. im assuming thats how it works. the new 1996 dryer will not mate with the 1987 evap. different threads. so thats where i am stuck at.... get a 1987 dryer and have a custom hose made from 1996 compressor to fit the 1987 dryer? or any ideas?