Getting Stiffed on an Side Job

My husband installs central air for a living, a friend of ours sister and husband were looking to have this done to their house. They had been asking our friend to connect them to my husband for months and eventually my husband agreed to meet with them. He was weary only because friends were involved. As it was they had the main part that was given to them by someone else when they bought the house, they said it was only a couple of years old and so one of the more costly parts was taken care of. My husband ran all the air ducts, and got everything in place. Took a few weekends, a part had to be ordered to connect the two and the union which made this part was on strike, so it took almost 2 months for it to come in. A very frustrating ordeal for ALL parties, but when it came in my husband showed them the paperwork with which it came and it showed the order date and the delivery date. Proving it was under no ones control. My husband went to install it and it did not work, turned out that the main part which they provided was not 2 years old but much older. In fact the machine they had could not even use this converter and the company that made this product no longer made these or had anything to do with it. When my husband called the guy he told him and said all you have to do is buy the $300 machine and I will switch it over for you for no extra charge. He basically just wanted to be done with this.The guy said that he would call him back and that was a month ago. The other day we heard from someone that they had someone else do the work. So in other words they bought the $300 part and probably paid someone $200 to install it because all the manual labor part was done and they stiffed my husband for $1800. Yes the situation was less then desirable for EVERONE involved and he knew that it was a bad situation for the owners too to have to wait for their air, but the situation only went bad because they lied about their system and how old it was. If they had a problem with anything they should have called and spoke with my husband not just decide that all the work he put into their house, and all the money he saved them more then $3000, was not important. From the start of the job to the very end they not once called us. If I had a problem with someone doing work on my house I would definitely let them know, not decide oh well they don't get paid. Is there anything we can do without a contract in place?

Your husband could take them to small claims for the value of the work done. He would not need to show his work and the timing of the work were reasonable under the circumstances; the home owners may agree to compromise and make some payment if it looks like it will go to court.